Hsp23

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005737 cytoplasm	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for cytoplasm localization. sHSP family members across species localize to the cytoplasm. Hsp23 has been experimentally shown to localize in the cytoplasm/cytosol of CNS cells in Drosophila (PMID:32437379). The IBA annotation is consistent with direct experimental evidence. Reason: Cytoplasmic localization is well supported by IBA phylogenetic inference and confirmed experimentally by immunofluorescence in CNS cells (PMID:32437379). Supporting Evidence: PMID:32437379 The data show that sHSP23 and sHSP26 localize in the cytoplasm of CNS cells, in particular in the optic lobes and the central nerve cord file:DROME/Hsp23/Hsp23-deep-research-falcon.md Hsp23 is reported as a cytoplasmic/cytosolic sHSP (in contrast to Hsp22, which is mitochondrial)
GO:0005634 nucleus	IBA GO_REF:0000033	MARK AS OVER ANNOTATED	Summary: IBA annotation for nuclear localization. Many mammalian sHSP orthologs (e.g. HSPB1/HSP27, alphaB-crystallin) localize to the nucleus. For Hsp23, direct experimental evidence shows cytoplasmic localization in CNS cells (PMID:32437379) but no specific nuclear localization has been reported. Reason: While the IBA inference is phylogenetically reasonable for the broader sHSP family, the available direct evidence for Drosophila Hsp23 shows cytoplasmic localization (PMID:32437379). No direct experimental evidence supports nuclear localization of Hsp23 specifically.
GO:0009408 response to heat	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for response to heat. All four classical Drosophila sHSPs are highly heat-inducible (PMID:26705243, PMID:16572729). This is a core conserved function across the sHSP family. Reason: Response to heat is a fundamental, conserved function of the sHSP family. Hsp23 is strongly heat-inducible as confirmed by qPCR (PMID:26705243). Supporting Evidence: PMID:26705243 The four classical small HSPs (HSP22, HSP23, HSP26, and HSP27) were all highly induced after a heat shock file:DROME/Hsp23/Hsp23-deep-research-falcon.md heat shock factor (HSF) is reported to bind tightly to the Hsp23 promoter after heat stress via heat shock elements
GO:0042026 protein refolding	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for protein refolding. sHSPs do not themselves refold proteins; they are holdases that maintain substrates in a refoldable state for subsequent HSP70-dependent refolding (PMID:16572729, PMID:26705243). The refolding capacity of sHSPs is partially dependent on an intact HSP70 machine (PMID:26705243). The IBA annotation captures the involvement of sHSPs in the refolding pathway. Reason: Although Hsp23 is primarily a holdase, it participates in the protein refolding pathway by maintaining substrates in a refoldable state. In the in vitro refolding assay, 30% of luciferase activity was recovered in the presence of Hsp23 (PMID:16572729). Supporting Evidence: PMID:16572729 more than 50% of luciferase activity was recovered when heat denaturation was performed in the presence of Hsp22, 40% with Hsp27, and 30% with Hsp23 or Hsp26
GO:0051082 unfolded protein binding	IBA GO_REF:0000033	MODIFY	Summary: IBA annotation for unfolded protein binding. GO:0051082 is proposed for obsoletion. sHSPs are classic holdases that bind unfolded/denatured proteins and prevent their aggregation in an ATP-independent manner (PMID:16572729). As holdases, the closest replacement term is GO:0140309 (unfolded protein carrier activity). Reason: GO:0051082 is proposed for obsoletion. As a holdase, Hsp23 prevents aggregation of unfolded proteins (PMID:16572729). GO:0140309 (unfolded protein carrier activity) is not appropriate because it is carrier-specific (per go-ontology#30552). Retain until a holdase chaperone activity NTR is created. Proposed replacements: unfolded protein binding (retain until holdase NTR is created) Supporting Evidence: file:DROME/Hsp23/Hsp23-deep-research-falcon.md a key mechanistic distinction emphasized in Drosophila-focused reviews is that sHSPs can prevent nonspecific protein aggregation in an ATP‑independent manner
GO:0005737 cytoplasm	IEA GO_REF:0000117	ACCEPT	Summary: IEA annotation from ARBA for cytoplasm localization. Consistent with IBA and IDA annotations for cytoplasm/cytosol. Redundant with better-evidenced annotations. Reason: This IEA annotation is consistent with the IBA and experimental (IDA cytosol) annotations. Acceptable as redundant support.
GO:0009408 response to heat	IEA GO_REF:0000117	ACCEPT	Summary: IEA annotation from ARBA for response to heat. Consistent with IBA and IDA annotations for the same term. Reason: This IEA annotation is consistent with the IDA and IBA annotations for the same term. Acceptable as redundant support.
GO:0042026 protein refolding	IEA GO_REF:0000117	ACCEPT	Summary: IEA annotation from ARBA for protein refolding. Consistent with IBA and IDA annotations. Reason: This IEA annotation is consistent with the IDA and IBA annotations for the same term. Acceptable as redundant support.
GO:0051082 unfolded protein binding	IEA GO_REF:0000117	MODIFY	Summary: IEA annotation from ARBA for unfolded protein binding. GO:0051082 is proposed for obsoletion. Same recommendation as for the IBA annotation. Reason: GO:0051082 is proposed for obsoletion. As a holdase, Hsp23 binds unfolded proteins and prevents their aggregation. GO:0140309 (unfolded protein holdase activity) is not appropriate because it is carrier-specific (escorting between cellular components, per go-ontology#30552), which does not describe in-situ holdase activity. Retain GO:0051082 until a holdase chaperone activity NTR is created, consistent with the IBA annotation. Proposed replacements: unfolded protein binding (retain until holdase NTR is created)
GO:0005515 protein binding	IPI PMID:38944040 Next-generation Drosophila protein interactome map and its f...	ACCEPT	Summary: IPI annotation for protein binding from a large-scale Drosophila interactome study. The with/from column indicates interaction with P02517 (Hsp26). This interaction is independently confirmed by co-immunoprecipitation (PMID:32437379). However, protein binding is uninformative; the interaction with Hsp26 should be captured more specifically. Reason: The interaction between Hsp23 and Hsp26 is well-documented by co-immunoprecipitation (PMID:32437379) and large-scale interactomics (PMID:38944040). While protein binding is uninformative as a GO term, the IPI evidence with a specific interactor is acceptable and the interaction is biologically meaningful for sHSP oligomerization. Supporting Evidence: PMID:32437379 These results confirm the physical interaction between sHSP23 and sHSP26
GO:0006457 protein folding	IDA PMID:16572729 Differences in the chaperone-like activities of the four mai...	ACCEPT	Summary: IDA annotation for protein folding based on Morrow et al. 2006 demonstrating chaperone-like activity. All four Drosophila sHSPs prevent heat-induced protein aggregation and maintain proteins in a refoldable state (PMID:16572729). Reason: Hsp23 has demonstrated chaperone-like activity in preventing heat-induced protein aggregation and maintaining substrates in a refoldable state (PMID:16572729). Protein folding is an appropriate broad process annotation for a chaperone. Supporting Evidence: PMID:16572729 Therefore, the 4 main sHsps of Drosophila share the ability to prevent heat-induced protein aggregation and are able to maintain proteins in a refoldable state, although with different efficiencies file:DROME/Hsp23/Hsp23-deep-research-falcon.md frame Hsp23 as part of the ATP-independent sHSP chaperone system that buffers proteotoxic stress by limiting aggregation and helping maintain protein homeostasis
GO:0044183 protein folding chaperone	IDA PMID:16572729 Differences in the chaperone-like activities of the four mai...	MODIFY	Summary: IDA annotation for protein folding chaperone. Morrow et al. (2006) demonstrated that Hsp23 has chaperone-like activity, though less efficient than Hsp22 or Hsp27, requiring a 5-fold molar excess for equivalent anti-aggregation. However, GO:0044183 is defined as an ATP-dependent protein folding chaperone (foldase), which does not accurately describe sHSPs that function as ATP-independent holdases. Reason: GO:0044183 (protein folding chaperone) is for foldases (ATP-dependent). Hsp23 is an ATP-independent holdase requiring HSP70 for actual refolding (PMID:26705243); Drosophila sHSP reviews reiterate that sHSPs prevent aggregation in an ATP-independent manner (file:DROME/Hsp23/Hsp23-deep-research-falcon.md). The correct replacement is GO:0051082 (unfolded protein binding / holdase activity). GO:0140309 (unfolded protein holdase activity) is not appropriate because it is carrier-specific (escorting between cellular components, per go-ontology#30552), which does not describe in-situ holdase activity. Retain GO:0051082 until a holdase chaperone activity NTR is created, consistent with the IBA annotation. Proposed replacements: unfolded protein binding (retain until holdase NTR is created) Supporting Evidence: PMID:16572729 A 5 M excess of Hsp23 and Hsp26 was required to obtain the same efficiency with either citrate synthase or luciferase as substrate PMID:26705243 the refolding capacity of D. melanogaster HSP27 and CG14207 is partially dependent on an intact HSP70 machine file:DROME/Hsp23/Hsp23-deep-research-falcon.md a key mechanistic distinction emphasized in Drosophila-focused reviews is that sHSPs can prevent nonspecific protein aggregation in an ATP‑independent manner
GO:0005829 cytosol	IDA PMID:32437379 Small heat shock proteins determine synapse number and neuro...	ACCEPT	Summary: IDA annotation for cytosol localization based on Santana et al. (2020). Immunofluorescence in third instar larval brain shows that sHSP23 and sHSP26 localize in the cytoplasm of CNS cells (PMID:32437379). The more specific cytosol annotation is appropriate. Reason: Direct experimental evidence from immunofluorescence shows cytoplasmic localization of Hsp23 in CNS cells (PMID:32437379). Cytosol is an appropriate specific term. Supporting Evidence: PMID:32437379 The data show that sHSP23 and sHSP26 localize in the cytoplasm of CNS cells, in particular in the optic lobes and the central nerve cord file:DROME/Hsp23/Hsp23-deep-research-falcon.md sHsp23 is observed in CNS cytoplasm and to concentrate at NMJ synaptic boutons together with sHsp26
GO:0006457 protein folding	ISM PMID:19715580 The small heat shock protein (sHSP) genes in the silkworm, B...	ACCEPT	Summary: ISM annotation for protein folding based on sequence model analysis. Li et al. (2009) performed comparative analysis of sHSP genes across insects, identifying conserved alpha-crystallin domains characteristic of chaperone function. Reason: The ISM evidence from comparative genomic analysis is consistent with experimental evidence (PMID:16572729) demonstrating chaperone activity. Supporting Evidence: PMID:19715580 sHSPs primarily have chaperone activity and reflect the response machine of organisms to some extreme stresses existing in environment
GO:0051082 unfolded protein binding	IDA PMID:16572729 Differences in the chaperone-like activities of the four mai...	MODIFY	Summary: IDA annotation for unfolded protein binding. GO:0051082 is proposed for obsoletion. Morrow et al. (2006) demonstrated that all four sHSPs bind denatured substrates, with Hsp23 requiring a 5-fold molar excess for efficient binding. Reason: GO:0051082 is proposed for obsoletion. The experimental evidence clearly demonstrates holdase activity (binding denatured substrates and preventing aggregation). GO:0140309 (unfolded protein holdase activity) is not appropriate because it is carrier-specific (escorting between cellular components, per go-ontology#30552), which does not describe in-situ holdase activity. Retain GO:0051082 until a holdase chaperone activity NTR is created, consistent with the IBA annotation. Proposed replacements: unfolded protein binding (retain until holdase NTR is created) Supporting Evidence: PMID:16572729 A 5 M excess of Hsp23 and Hsp26 was required to obtain the same efficiency with either citrate synthase or luciferase as substrate
GO:0051082 unfolded protein binding	ISM PMID:19715580 The small heat shock protein (sHSP) genes in the silkworm, B...	MODIFY	Summary: ISM annotation for unfolded protein binding from comparative sHSP genomics. GO:0051082 is proposed for obsoletion. Reason: GO:0051082 is proposed for obsoletion. As a holdase, Hsp23 binds unfolded proteins and prevents their thermal aggregation. GO:0140309 (unfolded protein holdase activity) is not appropriate because it is carrier-specific (escorting between cellular components, per go-ontology#30552), which does not describe in-situ holdase activity. Retain GO:0051082 until a holdase chaperone activity NTR is created, consistent with the IBA annotation. Proposed replacements: unfolded protein binding (retain until holdase NTR is created) Supporting Evidence: PMID:19715580 This stable multimeric structure formed by sHSPs has the function of molecular chaperone, which binds to the proteins and prevents them from thermal denaturation
GO:0009408 response to heat	IDA PMID:26705243 Specific protein homeostatic functions of small heat-shock p...	ACCEPT	Summary: IDA annotation for response to heat from Vos et al. (2016). This study confirmed that the four classical sHSPs are all highly heat-inducible by qPCR in S2 cells. Reason: Strongly supported by experimental evidence. Hsp23 is one of the most abundantly constitutively expressed sHSPs and is highly heat-inducible (PMID:26705243). Supporting Evidence: PMID:26705243 The four classical small HSPs (HSP22, HSP23, HSP26, and HSP27) were all highly induced after a heat shock
GO:0042026 protein refolding	IDA PMID:26705243 Specific protein homeostatic functions of small heat-shock p...	ACCEPT	Summary: IDA annotation for protein refolding from Vos et al. (2016). In cell-based luciferase refolding assays, overexpression of the classical sHSPs (HSP23, HSP26, HSP27) increased luciferase refolding in S2 cells (PMID:26705243). Reason: Cellular refolding assay confirms that Hsp23 overexpression enhances luciferase refolding. The refolding capacity requires HSP70 (PMID:26705243). Supporting Evidence: PMID:26705243 overexpression of the classical small HSPs (HSP23, HSP26, and HSP27) increased luciferase refolding
GO:0009631 cold acclimation	IEP PMID:16313561 Cold hardening and transcriptional change in Drosophila mela...	KEEP AS NON CORE	Summary: IEP annotation for cold acclimation. Qin et al. (2005) used microarray analysis to examine transcript changes during cold hardening in Drosophila. Hsp23 was identified among the stress proteins differentially expressed during cold hardening treatment. IEP (inferred from expression pattern) is appropriate for transcript upregulation data. Reason: Cold acclimation is a stress response that may involve sHSP chaperone activity but represents a pleiotropic environmental response rather than a core molecular function. The IEP evidence (transcript upregulation) is relatively weak. Supporting Evidence: PMID:16313561 stress proteins, including Hsp23, Hsp26, Hsp83 and Frost as well as membrane-associated proteins may contribute to the cold hardening response
GO:0005515 protein binding	IPI PMID:9514881 Cloning and developmental expression of a nuclear ubiquitin-...	ACCEPT	Summary: IPI annotation for protein binding based on Joanisse et al. (1998). The with/from column indicates interaction with FB:FBgn0010602 (DmUbc9, the SUMO-conjugating enzyme). This was demonstrated by yeast two-hybrid and confirmed by co-immunoprecipitation. Reason: The interaction between Hsp23 and DmUbc9 is experimentally validated by both yeast two-hybrid and co-immunoprecipitation (PMID:9514881). While protein binding is uninformative, the IPI evidence documents a specific interactor. Supporting Evidence: PMID:9514881 a Drosophila melanogaster homologue of yeast and human ubc9 (Dmubc9) was found to interact with Drosophila Hsp23
GO:0001666 response to hypoxia	IEP PMID:19401761 Distinct mechanisms underlying tolerance to intermittent and...	KEEP AS NON CORE	Summary: IEP annotation for response to hypoxia. Azad et al. (2009) showed by microarray and qPCR that Hsp23 is significantly upregulated during constant hypoxia in Drosophila. Reason: Hypoxia response is a stress response that involves sHSP chaperone activity but is a pleiotropic response rather than a core molecular function. The IEP evidence (transcript upregulation) supports involvement but not direct participation. Supporting Evidence: PMID:19401761 Heat shock proteins up-regulation (specifically Hsp23 and Hsp70) led to a significant increase in adult survival (as compared to controls) of P-element lines during CH
GO:0001666 response to hypoxia	IMP PMID:19401761 Distinct mechanisms underlying tolerance to intermittent and...	KEEP AS NON CORE	Summary: IMP annotation for response to hypoxia. Azad et al. (2009) showed that Hsp23 P-element lines with increased expression had significantly higher survival under constant hypoxia (55% survival vs 31% for controls). This functional evidence goes beyond expression data. Reason: The IMP evidence demonstrates a functional role for Hsp23 in hypoxia tolerance via increased survival of P-element lines. However, this represents a pleiotropic stress response phenotype rather than a core evolved function of Hsp23. Supporting Evidence: PMID:19401761 Heat shock proteins up-regulation (specifically Hsp23 and Hsp70) led to a significant increase in adult survival (as compared to controls) of P-element lines during CH

Core Functions

Hsp23 functions as an ATP-independent holdase chaperone that prevents heat-induced protein aggregation and maintains substrates in a refoldable state. Less efficient than Hsp22 or Hsp27, requiring a 5-fold molar excess for equivalent anti-aggregation activity (PMID:16572729). Refolding of substrates held by Hsp23 requires the HSP70 machine (PMID:26705243). Hsp23 physically interacts with Hsp26, and both proteins colocalize in the cytoplasm of CNS cells (PMID:32437379). Note - GO:0140309 is the closest available term for holdases, though the carrier semantics do not perfectly describe in-situ holdase activity.

Molecular Function:

unfolded protein binding

Directly Involved In:

protein folding

Cellular Locations:

cytosol

References

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

PMID:9514881

Cloning and developmental expression of a nuclear ubiquitin-conjugating enzyme (DmUbc9) that interacts with small heat shock proteins in Drosophila melanogaster.

DmUbc9 interacts with Hsp23 in yeast two-hybrid and co-immunoprecipitation assays.

"In a two hybrid screen designed to identify proteins that interact with small heat shock proteins (sHsps), a Drosophila melanogaster homologue of yeast and human ubc9 (Dmubc9) was found to interact with Drosophila Hsp23"

PMID:16313561

Cold hardening and transcriptional change in Drosophila melanogaster.

Hsp23 is among stress proteins differentially expressed during cold hardening treatment.

"Taken together, these assays suggest that stress proteins, including Hsp23, Hsp26, Hsp83 and Frost as well as membrane-associated proteins may contribute to the cold hardening response."

PMID:16572729

Differences in the chaperone-like activities of the four main small heat shock proteins of Drosophila melanogaster.

All four sHSPs have chaperone-like activity; Hsp23 requires 5-fold molar excess for equivalent efficiency.

"A 5 M excess of Hsp23 and Hsp26 was required to obtain the same efficiency with either citrate synthase or luciferase as substrate."
Approximately 30% of luciferase activity is recovered with Hsp23 in refolding assays.

"In an in vitro refolding assay with reticulocyte lysate, more than 50% of luciferase activity was recovered when heat denaturation was performed in the presence of Hsp22, 40% with Hsp27, and 30% with Hsp23 or Hsp26."

PMID:19401761

Distinct mechanisms underlying tolerance to intermittent and constant hypoxia in Drosophila melanogaster.

Hsp23 is upregulated during constant hypoxia; P-element lines show increased survival.

"Heat shock proteins up-regulation (specifically Hsp23 and Hsp70) led to a significant increase in adult survival (as compared to controls) of P-element lines during CH."

PMID:19715580

The small heat shock protein (sHSP) genes in the silkworm, Bombyx mori, and comparative analysis with other insect sHSP genes.

Comparative analysis identifies conserved alpha-crystallin domains across insect sHSPs.

"The sHSPs have an α-crystalling domain comprising about 100 amino acid residues, which is the conserved structure of all sHSP sequences [6-8]"

PMID:26705243

Specific protein homeostatic functions of small heat-shock proteins increase lifespan.

Hsp23 assists in HSP70-dependent refolding of luciferase in S2 cell-based assays.

"Consistent with in vitro data (Morrow et al., 2006), overexpression of the classical small HSPs (HSP23, HSP26, and HSP27) increased luciferase refolding (Fig"
All four classical sHSPs are highly heat-inducible.

"The four classical small HSPs (HSP22, HSP23, HSP26, and HSP27) were all highly induced after a heat shock (Fig"

PMID:32437379

Small heat shock proteins determine synapse number and neuronal activity during development.

Hsp23 and Hsp26 colocalize in the cytoplasm of CNS cells and physically interact.

"The data show that sHSP23 and sHSP26 localize in the cytoplasm of CNS cells, in particular in the optic lobes and the central nerve cord (Fig 2A and 2B`)"
Hsp23 and Hsp26 modulate synapse number during development.

"we suggest that sHSP23 and sHSP26 together form a complex that promotes synapse formation in presynaptic neurons, Pkm is an anti-synaptogenic element in neurons through, but not restricted to, the modulation of sHsp23 and sHsp26 (Fig 5C)."

PMID:38944040

Next-generation Drosophila protein interactome map and its functional implications.

Large-scale interactome confirms Hsp23-Hsp26 physical interaction.

"The network contains 32,668 interactions among 3,644 proteins, organized into 632 clusters representing putative functional modules"

file:DROME/Hsp23/Hsp23-deep-research-falcon.md

Falcon deep research report on Hsp23 (Drosophila melanogaster)

Hsp23 is a cytosolic small heat shock protein (HSP20/sHSP family) of Drosophila melanogaster (CG4463; UniProt P02516) containing the conserved alpha-crystallin domain, clustered with Hsp22, Hsp26 and Hsp27 at locus 67B; it is ~20.6 kDa and cytosolic.

"Hsp23 is one of the canonical sHSPs (clustered with other sHSP genes at cytological position **67B**) and is described as a ~**20.6 kDa** cytosolic protein"
As an sHSP, Hsp23 acts as an ATP-independent molecular chaperone (holdase) that prevents nonspecific protein aggregation, functioning within the proteostasis network.

"a key mechanistic distinction emphasized in Drosophila-focused reviews is that sHSPs can **prevent nonspecific protein aggregation in an ATP‑independent manner**"
Beyond generic chaperoning, Hsp23 is reported to bind cytoskeletal elements (actin and microtubules) and is linked to embryo morphogenetic processes such as ventral furrow formation.

"multiple syntheses cite evidence that Hsp23 can **bind cytoskeletal elements** (including **actin and microtubules**) and has been linked to **embryo morphogenetic processes**"
Hsp23 is a cytoplasmic/cytosolic sHSP, in contrast to the mitochondrial Hsp22; in the nervous system it localizes to CNS cytoplasm and concentrates at NMJ synaptic boutons together with sHsp26.

"sHsp23 is observed in **CNS cytoplasm** and to **concentrate at NMJ synaptic boutons** together with sHsp26"
Hsp23 transcription is regulated by the canonical heat-shock response (HSF binds the Hsp23 promoter via heat shock elements after heat stress), by dFOXO during oxidative stress, and by ecdysone during development.

"heat shock factor (**HSF**) is reported to bind tightly to the **Hsp23 promoter** after heat stress via heat shock elements"
dFOXO directly targets multiple inducible sHSP promoters including Hsp23, placing Hsp23 at the intersection of oxidative stress and proteostasis regulation.

"A mechanistic study of oxidative-stress transcriptional control in Drosophila reports that **dFOXO directly targets multiple sHSP promoters including Hsp23**"
Muscle-specific Hsp23 overexpression protects flight muscle against heat-stress-induced degeneration with both cell-autonomous and cell-nonautonomous (neuron/glia) protection, whereas Hsp70 overexpression does not protect in the same paradigm.

"**Muscle-specific Hsp23 overexpression** protects flight muscle and also provides **cell-nonautonomous protection** of motor neurons and glia after heat stress, whereas **Hsp70 overexpression does not** protect in the same paradigm"
Hsp23 overexpression reorganizes ubiquitinated proteins into perinuclear ring-like puncta and preserves the microtubule cytoskeleton after heat shock, linking Hsp23 to stress-resilient proteostasis and cytoskeletal integrity.

"Hsp23 overexpression is associated with **organized perinuclear ubiquitin puncta** and preservation of the **microtubule cytoskeleton** following heat shock"
In developing motor neurons, excess sHsp23 reduces synapse number (active zones per NMJ) and is not required for synapse formation, indicating dosage-sensitive effects on synapse development.

"In motor neurons, sHsp23 overexpression is reported to **reduce synapse number** (as quantified by active zones per NMJ) and is interpreted as **not required for synapse formation**"
Maternal loading/overexpression of Hsp23 in oocytes increases thermal tolerance of offspring embryos and improves larval performance, supporting a thermoprotective role during early development.

"developmental review evidence further indicates that **maternal loading/overexpression of Hsp23 in oocytes increases thermal tolerance of offspring embryos** and improves larval performance"

Deep Research

Falcon

(Hsp23-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 26 citations 2 artifacts 2026-05-30T16:14:27.480472

Edison artifact artifact-00 (text/markdown)

## Context ID: pqac-00000014 The requested panels showing the effects of HSP23 overexpression are found in Figures 5, 6, and 7. - Figure 5B shows that muscle-sp (image/png)

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research report: Drosophila melanogaster Hsp23 (CG4463; UniProt P02516) — functional annotation

0) Target verification (gene/protein identity)

The literature evidence used here explicitly maps Hsp23 to CG4463 and UniProt P02516 in Drosophila melanogaster, describing it as a cytosolic small heat shock protein (sHSP/HSP20 family) containing the conserved α‑crystallin domain, consistent with the UniProt-provided identification context. (dabbaghizadeh2018structureandfunction pages 51-55, morrow2015drosophilasmallheat pages 5-8, jagla2018developmentalexpressionand pages 1-3)

1) Key concepts and definitions (current understanding)

1.1 Small heat shock proteins (sHSPs)

Small heat shock proteins are a class of evolutionarily conserved molecular chaperones that are typically stress-inducible and are characterized by a conserved ~80 aa α‑crystallin domain; a key mechanistic distinction emphasized in Drosophila-focused reviews is that sHSPs can prevent nonspecific protein aggregation in an ATP‑independent manner, acting as part of the proteostasis network. (jagla2018developmentalexpressionand pages 1-3)

1.2 Hsp23 as an sHSP in Drosophila

In D. melanogaster, Hsp23 is one of the canonical sHSPs (clustered with other sHSP genes at cytological position 67B) and is described as a ~20.6 kDa cytosolic protein; it belongs to the same Drosophila sHSP group that includes Hsp22, Hsp26, and Hsp27 and shares the α‑crystallin domain typical of the family. (dabbaghizadeh2018structureandfunction pages 51-55, jagla2018developmentalexpressionand pages 1-3, dabbaghizadeh2018structureandfunction pages 48-51)

2) Molecular function and mechanism

2.1 Primary molecular function: ATP-independent chaperone/proteostasis factor

Direct functional descriptions in Drosophila sHSP reviews and developmental summaries frame Hsp23 as part of the ATP-independent sHSP chaperone system that buffers proteotoxic stress by limiting aggregation and helping maintain protein homeostasis, particularly during environmental stress and sensitive developmental windows. (jagla2018developmentalexpressionand pages 1-3, morrow2003heatshockproteins pages 1-2)

2.2 Cytoskeletal association and morphogenesis

Beyond generic chaperoning, multiple syntheses cite evidence that Hsp23 can bind cytoskeletal elements (including actin and microtubules) and has been linked to embryo morphogenetic processes (e.g., ventral furrow formation) and association with microtubule-related complexes together with other sHSPs. (morrow2015drosophilasmallheat pages 5-8, dabbaghizadeh2018structureandfunction pages 55-58)

Interpretation: these observations support a model in which Hsp23’s chaperone-like activity is deployed in spatially organized cellular contexts (e.g., cytoskeleton-associated proteostasis), potentially stabilizing or coordinating folding/assembly of cytoskeleton-proximal proteins under stress and in development. (morrow2015drosophilasmallheat pages 5-8, kawasaki2016smallheatshock pages 5-6)

3) Subcellular localization (where it acts)

3.1 Predominantly cytosolic/cytoplasmic

Hsp23 is reported as a cytoplasmic/cytosolic sHSP (in contrast to Hsp22, which is mitochondrial), consistent with its proposed roles in cytoplasmic proteostasis and cytoskeletal interactions. (dabbaghizadeh2018structureandfunction pages 51-55, dabbaghizadeh2018structureandfunction pages 55-58)

3.2 CNS and synapse-associated localization

In a Drosophila neurodevelopmental study focused on synapse regulation, sHsp23 is observed in CNS cytoplasm and to concentrate at NMJ synaptic boutons together with sHsp26, and the proteins are reported/predicted to physically interact in that context. (santana2020smallheatshock pages 4-5)

3.3 Perinuclear proteostasis-associated organization in muscle under heat stress

In a heat-shock-induced flight muscle degeneration model, muscle-directed Hsp23 overexpression reshapes the distribution of ubiquitinated proteins into perinuclear ring-like puncta and preserves the perinuclear microtubule network under stress, implying that Hsp23 can organize stress-associated proteostasis near the nucleus and cytoskeleton. (kawasaki2016smallheatshock pages 5-6, kawasaki2016smallheatshock media 8b569353)

4) Regulation and pathway context

4.1 Canonical heat shock response: HSF → Hsp23

Hsp23 is described as heat-inducible and among strongly heat-responsive sHSP transcripts; heat shock factor (HSF) is reported to bind tightly to the Hsp23 promoter after heat stress via heat shock elements. (dabbaghizadeh2018structureandfunction pages 51-55)

4.2 Oxidative stress/insulin signaling axis: dFOXO → Hsp23

A mechanistic study of oxidative-stress transcriptional control in Drosophila reports that dFOXO directly targets multiple sHSP promoters including Hsp23, and that inducible sHSPs are activated when dFOXO activity rises during oxidative stress, positioning Hsp23 at the intersection of oxidative stress and proteostasis regulation. (Donovan & Marr, J Biol Chem, Sep 2016, https://doi.org/10.1074/jbc.m116.723049) (donovan2016dfoxoactivateslarge pages 2-3)

4.3 Developmental hormone regulation and chromatin features

Drosophila developmental reviews indicate that sHSP promoters (including Hsp23) are maintained in an active chromatin state enabling both HSF-dependent and HSF-independent expression, and that ecdysone can regulate ovarian and larval/prepupal sHSP expression through elements distinct from classical heat shock elements; GA repeat features (binding GAGA factors) are highlighted as a general promoter property. (Jagla et al., Int J Mol Sci, Nov 2018, https://doi.org/10.3390/ijms19113441) (jagla2018developmentalexpressionand pages 1-3)

5) Biological roles: development, stress tolerance, and aging

5.1 Developmental/tissue expression

Multiple sources describe Hsp23 as developmentally regulated and tissue-specific. Zygotic expression is reported to begin at embryonic stage 11 and be restricted to the CNS, including specific neuronal/glial lineages (MP2 neurons, VUM cells, dorsal midline glia). (Morrow & Tanguay, Semin Cell Dev Biol, Oct 2003, https://doi.org/10.1016/j.semcdb.2003.09.023) (morrow2003heatshockproteins pages 1-2)

Transcriptome-based summaries also highlight high Hsp23 transcript levels in early embryos (4–6 h AEL) and testis, and high to extremely high transcription in the CNS. (jagla2018developmentalexpressionand pages 1-3)

5.2 Germline/ovary isoforms and maternal effects

Hsp23 is reported to exist in at least two isoforms in ovaries: a native form (Hsp23a) present without stress and a more acidic form (Hsp23b) induced by heat shock; developmental review evidence further indicates that maternal loading/overexpression of Hsp23 in oocytes increases thermal tolerance of offspring embryos and improves larval performance, supporting a direct thermoprotective function during early development. (jagla2018developmentalexpressionand pages 3-6)

5.3 Aging-associated induction

Hsp23 is described as upregulated with aging (in particular in thoraces/abdomen), with one synthesis reporting induction up to ~5-fold in those tissues. (dabbaghizadeh2018structureandfunction pages 55-58)

6) Perturbation phenotypes and functional studies (experimental evidence)

6.1 Flight muscle proteostasis and degeneration protection (heat stress model)

A primary experimental study developed a Drosophila model of heat-shock-stress-induced flight motor degeneration and showed that heat stress causes a prominent failure of flight muscle proteostasis, including increased ubiquitin-positive aggregates; in this system:

Muscle-specific Hsp23 overexpression protects flight muscle and also provides cell-nonautonomous protection of motor neurons and glia after heat stress, whereas Hsp70 overexpression does not protect in the same paradigm. (Kawasaki et al., Dis Model Mech, Sep 2016, https://doi.org/10.1242/dmm.026385) (kawasaki2016smallheatshock pages 4-5)
Hsp23 overexpression is associated with organized perinuclear ubiquitin puncta and preservation of the microtubule cytoskeleton following heat shock, supporting a mechanistic link between Hsp23 and stress-resilient proteostasis/cytoskeletal integrity. (kawasaki2016smallheatshock pages 5-6, kawasaki2016smallheatshock media 8b569353)

Statistics/data reported in the study excerpt: group sizes are explicitly given for key comparisons (e.g., WT no-HS n=10, HS n=10; Hsp23 OE no-HS n=6, HS n=8; Hsp70 OE no-HS n=7, HS n=8), with significance threshold reported as P≤0.01 for relevant comparisons. (kawasaki2016smallheatshock pages 4-5)

6.2 Synapse number and neuronal activity (developmental context)

In motor neurons, sHsp23 overexpression is reported to reduce synapse number (as quantified by active zones per NMJ) and is interpreted as not required for synapse formation, but detrimental in excess, suggesting dosage sensitivity and a role in tuning synapse development/neuronal activity. (Santana et al., PLOS ONE, May 2020, https://doi.org/10.1371/journal.pone.0233231) (santana2020smallheatshock pages 4-5)

6.3 Loss-of-function/essentiality and redundancy

Review-level synthesis suggests that elimination/loss of Hsp23 often produces no obvious deleterious developmental phenotype under standard laboratory conditions, consistent with redundancy among sHSPs; however, other syntheses cite that preventing Hsp23 expression can reduce lifespan and impair stress resistance, indicating context dependence (environmental conditions, tissue specificity, genetic background). (morrow2015drosophilasmallheat pages 5-8, dabbaghizadeh2018structureandfunction pages 51-55)

7) Recent developments and latest research (2023–2024 prioritized)

7.1 2023: pharmacologic TOR pathway modulation alters Hsp23 among chaperones in fly CNS

A 2023 transcriptomic analysis of Torin-2 (TORC1/2 inhibitor) effects in Drosophila heads reports that “protein folding (heat shock proteins)” pathways are altered and lists Hsp23 among heat shock proteins/chaperones affected in the CNS transcriptional response. (Vershinina et al., Int J Mol Sci, May 2023, https://doi.org/10.3390/ijms24109095) (kawasaki2016smallheatshock media 530d147d)

Interpretation: while not Hsp23-specific mechanistic work, this links Hsp23 transcriptional modulation to nutrient-sensing/geroprotective pharmacology contexts and supports ongoing use of Hsp23 as a stress/proteostasis-responsive node in systems-level studies. (kawasaki2016smallheatshock media 530d147d)

7.2 2024: nuclear/cytoskeletal factors modulate heat shock gene expression including Hsp23 (metadata-level)

A 2024 study on Moesin–Mediator complex interactions reports effects on expression of heat shock genes including Hsp23 (from retrieved metadata/snippet), pointing to continued refinement of the transcriptional machinery controlling Hsp genes beyond HSF itself. (Kristó et al., Open Biology, Oct 2024, https://doi.org/10.1098/rsob.240110) (kawasaki2016smallheatshock media 530d147d)

Limitation: Full quantitative details for Hsp23 changes in this 2024 paper were not extractable from the available evidence snippets in this run, so no numeric claim is made here. (kawasaki2016smallheatshock media 530d147d)

8) Current applications and real-world implementations

Stress physiology and degeneration models in Drosophila: Hsp23 is actively used as a manipulable effector in environmental stress–induced muscle degeneration paradigms to dissect proteostasis, tissue vulnerability, and cell-nonautonomous protection mechanisms. (kawasaki2016smallheatshock pages 4-5)
Developmental neurobiology: Hsp23 is used as a factor influencing synapse development/activity, with overexpression and knockdown strategies in motor neurons as an implementation of functional annotation at the organismal NMJ. (santana2020smallheatshock pages 4-5)
Developmental thermotolerance engineering (maternal effects): manipulating Hsp23 in the female germline/oocytes provides a functional route to test embryo thermoprotection, relevant to adaptation to thermal extremes. (jagla2018developmentalexpressionand pages 3-6)
Aging/proteostasis biomarkers: Hsp23’s age-associated upregulation supports its use as a marker/readout in studies connecting aging, stress responses, and proteostasis systems. (dabbaghizadeh2018structureandfunction pages 55-58, morrow2003heatshockproteins pages 1-2)

9) Expert opinions and authoritative synthesis (interpretive analysis)

Authoritative Drosophila-focused reviews emphasize that the Drosophila sHSPs (including Hsp23) are not only acute heat-shock responders but also show distinct developmental programs and tissue specificity, supporting the modern view that sHSPs are deployed for developmental robustness as well as stress survival. (morrow2015drosophilasmallheat pages 5-8, jagla2018developmentalexpressionand pages 1-3)

Mechanistic integration supported by the evidence indicates that Hsp23 lies at an intersection of:
* canonical heat-shock transcription (HSF) (dabbaghizadeh2018structureandfunction pages 51-55),
* oxidative stress/insulin signaling (dFOXO) (donovan2016dfoxoactivateslarge pages 2-3), and
* developmental endocrine regulation (ecdysone) with chromatin-based promoter priming (jagla2018developmentalexpressionand pages 1-3),
consistent with a role as a context-dependent cytosolic proteostasis factor deployed across stress and development. (jagla2018developmentalexpressionand pages 1-3)

10) Key statistics and data points (from retrieved sources)

Protein size/localization: Hsp23 is reported as ~20.6 kDa and cytosolic. (dabbaghizadeh2018structureandfunction pages 51-55)
Aging induction: a synthesis reports age-associated induction up to ~5-fold in thorax/abdomen. (dabbaghizadeh2018structureandfunction pages 55-58)
Heat-stress degeneration model sample sizes: WT no-HS n=10, HS n=10; HSF OE no-HS n=6, HS n=6; Hsp23 OE no-HS n=6, HS n=8; Hsp70 OE no-HS n=7, HS n=8; with P≤0.01 criteria reported for key effects. (kawasaki2016smallheatshock pages 4-5)

11) Visual evidence from primary literature (figures)

Cropped figure regions from Kawasaki et al. show that muscle-specific Hsp23 overexpression preserves neuromuscular structure/function and reorganizes ubiquitinated proteins while maintaining microtubule integrity after heat shock. (kawasaki2016smallheatshock media 8b569353, kawasaki2016smallheatshock media 530d147d, kawasaki2016smallheatshock media f1945a67)

12) Evidence summary table

Aspect	Key findings	Best supporting sources
identity/domains	- Verified target is Drosophila melanogaster Hsp23 = CG4463 = UniProt P02516. - Member of the small heat shock protein (sHSP/HSP20) family with the conserved α-crystallin domain; Drosophila encodes 12 sHsps, with Hsp23 among the canonical clustered genes at 67B. - Reported size is ~20.6 kDa and Hsp23 is described as a cytosolic sHSP.	Jagla et al., 2018, https://doi.org/10.3390/ijms19113441 (jagla2018developmentalexpressionand pages 1-3); Morrow & Tanguay, 2015, https://doi.org/10.1007/978-3-319-16077-1_25 (morrow2015drosophilasmallheat pages 5-8); Dabbaghizadeh, 2018 (dabbaghizadeh2018structureandfunction pages 51-55, dabbaghizadeh2018structureandfunction pages 48-51)
molecular function	- As an sHSP, Hsp23 is inferred to act as an ATP-independent molecular chaperone that helps prevent nonspecific protein aggregation. - Hsp23 is implicated in proteostasis maintenance during environmental stress and in development. - Additional evidence links Hsp23 to cytoskeletal interactions with actin and microtubules, consistent with roles in morphogenesis and structural protection.	Jagla et al., 2018, https://doi.org/10.3390/ijms19113441 (jagla2018developmentalexpressionand pages 1-3); Morrow & Tanguay, 2015, https://doi.org/10.1007/978-3-319-16077-1_25 (morrow2015drosophilasmallheat pages 5-8); Dabbaghizadeh, 2018 (dabbaghizadeh2018structureandfunction pages 55-58)
localization	- Hsp23 is reported as primarily cytoplasmic/cytosolic rather than mitochondrial. - In the nervous system study, sHsp23 localizes in CNS cytoplasm and is enriched at NMJ synaptic boutons with sHsp26. - In stressed flight muscle, HSP23 overexpression reorganizes ubiquitin-positive material into perinuclear ring-like puncta and is associated with preservation of the microtubule network.	Dabbaghizadeh, 2018 (dabbaghizadeh2018structureandfunction pages 51-55, dabbaghizadeh2018structureandfunction pages 55-58); Santana et al., 2020, https://doi.org/10.1371/journal.pone.0233231 (santana2020smallheatshock pages 4-5); Kawasaki et al., 2016, https://doi.org/10.1242/dmm.026385 (kawasaki2016smallheatshock pages 5-6, kawasaki2016smallheatshock media 8b569353)
regulation	- HSF binds the Hsp23 promoter after heat stress; Hsp23 is strongly heat inducible and also reported as cold inducible. - dFOXO directly targets inducible sHSP genes including Hsp23 during oxidative stress, placing Hsp23 in FOXO-linked proteostasis control. - Hsp23 expression can also be induced by ecdysone, and sHsp promoters remain in an active chromatin state permitting HSF-dependent and HSF-independent transcription.	Donovan & Marr, 2016, https://doi.org/10.1074/jbc.m116.723049 (donovan2016dfoxoactivateslarge pages 2-3); Jagla et al., 2018, https://doi.org/10.3390/ijms19113441 (jagla2018developmentalexpressionand pages 1-3); Dabbaghizadeh, 2018 (dabbaghizadeh2018structureandfunction pages 51-55, dabbaghizadeh2018structureandfunction pages 55-58)
developmental/tissue expression	- Hsp23 is developmentally regulated and maternally relevant; zygotic expression begins at embryonic stage 11 and is restricted to the CNS, including MP2 neurons, VUM cells and later dorsal midline glia. - High expression is reported in early embryos (4–6 h AEL), testis, and broadly in the CNS; expression is also seen in germline, nervous system, muscle/heart, and adult gonads/brain. - In ovaries, at least two isoforms are described: Hsp23a present without stress and more acidic Hsp23b induced by heat shock.	Morrow & Tanguay, 2003, https://doi.org/10.1016/j.semcdb.2003.09.023 (morrow2003heatshockproteins pages 1-2); Jagla et al., 2018, https://doi.org/10.3390/ijms19113441 (jagla2018developmentalexpressionand pages 3-6, jagla2018developmentalexpressionand pages 1-3); Morrow & Tanguay, 2015, https://doi.org/10.1007/978-3-319-16077-1_25 (morrow2015drosophilasmallheat pages 5-8)
phenotypes/functional studies	- Muscle-specific HSP23 overexpression protects against heat-shock-induced degeneration of the flight motor, with both cell-autonomous muscle protection and cell-nonautonomous protection of neurons and glia; HSP70 overexpression did not protect in the same assay. - HSP23 overexpression preserves muscle proteostasis, promotes clearance/reorganization of ubiquitinated aggregates, and protects the microtubule cytoskeleton after heat shock. - In developing motor neurons, excess sHsp23 reduces synapse number, suggesting dosage-sensitive effects; maternal loading/overexpression of Hsp23 in oocytes improves embryo thermal tolerance and later larval performance.	Kawasaki et al., 2016, https://doi.org/10.1242/dmm.026385 (kawasaki2016smallheatshock pages 5-6, kawasaki2016smallheatshock pages 4-5, kawasaki2016smallheatshock media 8b569353); Santana et al., 2020, https://doi.org/10.1371/journal.pone.0233231 (santana2020smallheatshock pages 4-5, santana2020smallheatshock pages 2-4); Jagla et al., 2018, https://doi.org/10.3390/ijms19113441 (jagla2018developmentalexpressionand pages 3-6)
quantitative data	- Hsp23 is reported to increase with age, including up to ~5-fold in thoraces/abdomen in one synthesis. - Experimental sample sizes for the flight-muscle protection assay included WT n=10/10 (no HS/HS), HSF OE n=6/6, HSP23 OE n=6/8, and HSP70 OE n=7/8; protection reached P≤0.01 in the cited analysis. - Figure-based evidence shows preserved muscle membrane potential, protected neuromuscular synapses, organized ubiquitin puncta, and preserved microtubules with HSP23 OE after HS, although exact numeric values were not extracted from the available context.	Dabbaghizadeh, 2018 (dabbaghizadeh2018structureandfunction pages 55-58); Kawasaki et al., 2016, https://doi.org/10.1242/dmm.026385 (kawasaki2016smallheatshock pages 5-6, kawasaki2016smallheatshock pages 4-5, kawasaki2016smallheatshock media 8b569353)

Table: This table summarizes evidence-based functional annotation for Drosophila melanogaster Hsp23 (CG4463; UniProt P02516), including identity, regulation, localization, developmental expression, and phenotype data. It is designed as a compact reference using only claims supported by the cited evidence IDs.

13) Gaps and recommendations for further annotation work

Direct biochemical chaperone assays for Hsp23 specifically (e.g., defined client proteins, oligomeric states, and quantitative anti-aggregation assays) were not present in the retrieved evidence snippets; the ATP-independent chaperone role is supported at the family level and by in vivo proteostasis phenotypes. (jagla2018developmentalexpressionand pages 1-3, kawasaki2016smallheatshock pages 5-6)
2023–2024 Hsp23-specific mechanistic papers in D. melanogaster were limited in the retrieved corpus; the newest accessible items were systems-level transcriptomics (2023) and heat shock gene regulation machinery (2024) without extractable numeric Hsp23 effects from snippets. (kawasaki2016smallheatshock media 530d147d)

References (URLs and publication dates)

Morrow G, Tanguay RM. Heat shock proteins and aging in Drosophila melanogaster. Oct 2003. https://doi.org/10.1016/j.semcdb.2003.09.023 (morrow2003heatshockproteins pages 1-2)
Morrow G, Tanguay RM. Drosophila Small Heat Shock Proteins: An Update on Their Features and Functions. Jan 2015. https://doi.org/10.1007/978-3-319-16077-1_25 (morrow2015drosophilasmallheat pages 5-8)
Donovan MR, Marr MT. dFOXO Activates Large and Small Heat Shock Protein Genes in Response to Oxidative Stress to Maintain Proteostasis in Drosophila. Sep 2016. https://doi.org/10.1074/jbc.m116.723049 (donovan2016dfoxoactivateslarge pages 2-3)
Kawasaki F, et al. Small heat shock proteins mediate cell-autonomous and -nonautonomous protection in a Drosophila model for environmental-stress-induced degeneration. Sep 2016. https://doi.org/10.1242/dmm.026385 (kawasaki2016smallheatshock pages 5-6, kawasaki2016smallheatshock pages 4-5)
Jagla T, et al. Developmental expression and functions of the small heat shock proteins in Drosophila. Nov 2018. https://doi.org/10.3390/ijms19113441 (jagla2018developmentalexpressionand pages 3-6, jagla2018developmentalexpressionand pages 1-3)
Santana E, et al. Small heat shock proteins determine synapse number and neuronal activity during development. May 2020. https://doi.org/10.1371/journal.pone.0233231 (santana2020smallheatshock pages 4-5, santana2020smallheatshock pages 2-4)
Vershinina YS, et al. Transcriptomic Analysis of the Effect of Torin-2 on the Central Nervous System of Drosophila melanogaster. May 2023. https://doi.org/10.3390/ijms24109095 (kawasaki2016smallheatshock media 530d147d)
Kristó I, et al. Moesin contributes to heat shock gene response through direct binding to the Med15 subunit of the Mediator complex in the nucleus. Oct 2024. https://doi.org/10.1098/rsob.240110 (kawasaki2016smallheatshock media 530d147d)

References

(dabbaghizadeh2018structureandfunction pages 51-55): A Dabbaghizadeh. Structure and function of mitochondrial small heat shock protein 22 in drosophila melanogaster. Unknown journal, 2018.
(morrow2015drosophilasmallheat pages 5-8): Geneviève Morrow and Robert M. Tanguay. Drosophila small heat shock proteins: an update on their features and functions. ArXiv, pages 579-606, Jan 2015. URL: https://doi.org/10.1007/978-3-319-16077-1_25, doi:10.1007/978-3-319-16077-1_25. This article has 37 citations.
(jagla2018developmentalexpressionand pages 1-3): Teresa Jagla, Magda Dubińska-Magiera, Preethi Poovathumkadavil, Małgorzata Daczewska, and Krzysztof Jagla. Developmental expression and functions of the small heat shock proteins in drosophila. International Journal of Molecular Sciences, 19:3441, Nov 2018. URL: https://doi.org/10.3390/ijms19113441, doi:10.3390/ijms19113441. This article has 54 citations.
(dabbaghizadeh2018structureandfunction pages 48-51): A Dabbaghizadeh. Structure and function of mitochondrial small heat shock protein 22 in drosophila melanogaster. Unknown journal, 2018.
(morrow2003heatshockproteins pages 1-2): Geneviève Morrow and Robert M. Tanguay. Heat shock proteins and aging in drosophila melanogaster. Seminars in cell & developmental biology, 14 5:291-9, Oct 2003. URL: https://doi.org/10.1016/j.semcdb.2003.09.023, doi:10.1016/j.semcdb.2003.09.023. This article has 136 citations and is from a peer-reviewed journal.
(dabbaghizadeh2018structureandfunction pages 55-58): A Dabbaghizadeh. Structure and function of mitochondrial small heat shock protein 22 in drosophila melanogaster. Unknown journal, 2018.
(kawasaki2016smallheatshock pages 5-6): Fumiko Kawasaki, Noelle L. Koonce, Linda Guo, Shahroz Fatima, Catherine Qiu, Mackenzie T. Moon, Yunzhen Zheng, and Richard W. Ordway. Small heat shock proteins mediate cell-autonomous and -nonautonomous protection in a drosophila model for environmental-stress-induced degeneration. Disease Models & Mechanisms, 9:953-964, Sep 2016. URL: https://doi.org/10.1242/dmm.026385, doi:10.1242/dmm.026385. This article has 30 citations and is from a domain leading peer-reviewed journal.
(santana2020smallheatshock pages 4-5): Elena Santana, Teresa de los Reyes, and Sergio Casas-Tintó. Small heat shock proteins determine synapse number and neuronal activity during development. PLOS ONE, 15:e0233231, May 2020. URL: https://doi.org/10.1371/journal.pone.0233231, doi:10.1371/journal.pone.0233231. This article has 23 citations and is from a peer-reviewed journal.
(kawasaki2016smallheatshock media 8b569353): Fumiko Kawasaki, Noelle L. Koonce, Linda Guo, Shahroz Fatima, Catherine Qiu, Mackenzie T. Moon, Yunzhen Zheng, and Richard W. Ordway. Small heat shock proteins mediate cell-autonomous and -nonautonomous protection in a drosophila model for environmental-stress-induced degeneration. Disease Models & Mechanisms, 9:953-964, Sep 2016. URL: https://doi.org/10.1242/dmm.026385, doi:10.1242/dmm.026385. This article has 30 citations and is from a domain leading peer-reviewed journal.
(donovan2016dfoxoactivateslarge pages 2-3): Marissa R. Donovan and Michael T. Marr. Dfoxo activates large and small heat shock protein genes in response to oxidative stress to maintain proteostasis in drosophila. Journal of Biological Chemistry, 291:19042-19050, Sep 2016. URL: https://doi.org/10.1074/jbc.m116.723049, doi:10.1074/jbc.m116.723049. This article has 52 citations and is from a domain leading peer-reviewed journal.
(jagla2018developmentalexpressionand pages 3-6): Teresa Jagla, Magda Dubińska-Magiera, Preethi Poovathumkadavil, Małgorzata Daczewska, and Krzysztof Jagla. Developmental expression and functions of the small heat shock proteins in drosophila. International Journal of Molecular Sciences, 19:3441, Nov 2018. URL: https://doi.org/10.3390/ijms19113441, doi:10.3390/ijms19113441. This article has 54 citations.
(kawasaki2016smallheatshock pages 4-5): Fumiko Kawasaki, Noelle L. Koonce, Linda Guo, Shahroz Fatima, Catherine Qiu, Mackenzie T. Moon, Yunzhen Zheng, and Richard W. Ordway. Small heat shock proteins mediate cell-autonomous and -nonautonomous protection in a drosophila model for environmental-stress-induced degeneration. Disease Models & Mechanisms, 9:953-964, Sep 2016. URL: https://doi.org/10.1242/dmm.026385, doi:10.1242/dmm.026385. This article has 30 citations and is from a domain leading peer-reviewed journal.
(kawasaki2016smallheatshock media 530d147d): Fumiko Kawasaki, Noelle L. Koonce, Linda Guo, Shahroz Fatima, Catherine Qiu, Mackenzie T. Moon, Yunzhen Zheng, and Richard W. Ordway. Small heat shock proteins mediate cell-autonomous and -nonautonomous protection in a drosophila model for environmental-stress-induced degeneration. Disease Models & Mechanisms, 9:953-964, Sep 2016. URL: https://doi.org/10.1242/dmm.026385, doi:10.1242/dmm.026385. This article has 30 citations and is from a domain leading peer-reviewed journal.
(kawasaki2016smallheatshock media f1945a67): Fumiko Kawasaki, Noelle L. Koonce, Linda Guo, Shahroz Fatima, Catherine Qiu, Mackenzie T. Moon, Yunzhen Zheng, and Richard W. Ordway. Small heat shock proteins mediate cell-autonomous and -nonautonomous protection in a drosophila model for environmental-stress-induced degeneration. Disease Models & Mechanisms, 9:953-964, Sep 2016. URL: https://doi.org/10.1242/dmm.026385, doi:10.1242/dmm.026385. This article has 30 citations and is from a domain leading peer-reviewed journal.
(santana2020smallheatshock pages 2-4): Elena Santana, Teresa de los Reyes, and Sergio Casas-Tintó. Small heat shock proteins determine synapse number and neuronal activity during development. PLOS ONE, 15:e0233231, May 2020. URL: https://doi.org/10.1371/journal.pone.0233231, doi:10.1371/journal.pone.0233231. This article has 23 citations and is from a peer-reviewed journal.

Artifacts

Edison artifact artifact-00

Citations

jagla2018developmentalexpressionand pages 1-3
santana2020smallheatshock pages 4-5
dabbaghizadeh2018structureandfunction pages 51-55
donovan2016dfoxoactivateslarge pages 2-3
morrow2003heatshockproteins pages 1-2
jagla2018developmentalexpressionand pages 3-6
dabbaghizadeh2018structureandfunction pages 55-58
kawasaki2016smallheatshock pages 4-5
morrow2015drosophilasmallheat pages 5-8
dabbaghizadeh2018structureandfunction pages 48-51
kawasaki2016smallheatshock pages 5-6
santana2020smallheatshock pages 2-4
https://doi.org/10.1074/jbc.m116.723049
https://doi.org/10.3390/ijms19113441
https://doi.org/10.1016/j.semcdb.2003.09.023
https://doi.org/10.1242/dmm.026385
https://doi.org/10.1371/journal.pone.0233231
https://doi.org/10.3390/ijms24109095
https://doi.org/10.1098/rsob.240110
https://doi.org/10.1007/978-3-319-16077-1_25
https://doi.org/10.1007/978-3-319-16077-1_25,
https://doi.org/10.3390/ijms19113441,
https://doi.org/10.1016/j.semcdb.2003.09.023,
https://doi.org/10.1242/dmm.026385,
https://doi.org/10.1371/journal.pone.0233231,
https://doi.org/10.1074/jbc.m116.723049,

📄 View Raw YAML

id: P02516
gene_symbol: Hsp23
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:7227
  label: Drosophila melanogaster
description: Hsp23 is a small heat shock protein (sHSP) of Drosophila melanogaster that localizes to the cytoplasm/cytosol (PMID:32437379). It is one of four classical Drosophila sHSPs (Hsp22, Hsp23, Hsp26, Hsp27) encoded in a gene cluster at chromosomal locus 67B. All four sHSPs share a conserved alpha-crystallin domain and possess ATP-independent chaperone-like (holdase) activity, preventing heat-induced protein aggregation and maintaining substrates in a refoldable state (PMID:16572729). Hsp23 requires a 5-fold molar excess over substrate (citrate synthase or luciferase) for equivalent anti-aggregation activity compared to Hsp22 and Hsp27 (PMID:16572729). Approximately 30% of luciferase activity is recovered in in vitro refolding assays with Hsp23 (PMID:16572729). Hsp23 interacts physically with Hsp26, and both proteins colocalize in CNS neurons, playing a role in synaptogenesis during development (PMID:32437379). Hsp23 also interacts with the SUMO-conjugating enzyme DmUbc9 (PMID:9514881). Hsp23 is upregulated during cold hardening (PMID:16313561) and constant hypoxia, where it plays an important role in hypoxia tolerance (PMID:19401761). GO:0051082 (unfolded protein binding) is proposed for obsoletion; as a classic holdase, the closest replacement is GO:0140309 (unfolded protein carrier activity), though the carrier semantics (escorting between cellular components) do not perfectly describe in-situ holdase activity.
existing_annotations:
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: IBA annotation for cytoplasm localization. sHSP family members across species localize to the cytoplasm. Hsp23 has been experimentally shown to localize in the cytoplasm/cytosol of CNS cells in Drosophila (PMID:32437379). The IBA annotation is consistent with direct experimental evidence.
    action: ACCEPT
    reason: Cytoplasmic localization is well supported by IBA phylogenetic inference and confirmed experimentally by immunofluorescence in CNS cells (PMID:32437379).
    supported_by:
    - reference_id: PMID:32437379
      supporting_text: The data show that sHSP23 and sHSP26 localize in the cytoplasm of CNS cells, in particular in the optic lobes and the central nerve cord
    - reference_id: file:DROME/Hsp23/Hsp23-deep-research-falcon.md
      supporting_text: |-
        Hsp23 is reported as a **cytoplasmic/cytosolic** sHSP (in contrast to Hsp22, which is mitochondrial)
    additional_reference_ids:
    - file:DROME/Hsp23/Hsp23-deep-research-falcon.md
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: IBA annotation for nuclear localization. Many mammalian sHSP orthologs (e.g. HSPB1/HSP27, alphaB-crystallin) localize to the nucleus. For Hsp23, direct experimental evidence shows cytoplasmic localization in CNS cells (PMID:32437379) but no specific nuclear localization has been reported.
    action: MARK_AS_OVER_ANNOTATED
    reason: While the IBA inference is phylogenetically reasonable for the broader sHSP family, the available direct evidence for Drosophila Hsp23 shows cytoplasmic localization (PMID:32437379). No direct experimental evidence supports nuclear localization of Hsp23 specifically.
- term:
    id: GO:0009408
    label: response to heat
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: IBA annotation for response to heat. All four classical Drosophila sHSPs are highly heat-inducible (PMID:26705243, PMID:16572729). This is a core conserved function across the sHSP family.
    action: ACCEPT
    reason: Response to heat is a fundamental, conserved function of the sHSP family. Hsp23 is strongly heat-inducible as confirmed by qPCR (PMID:26705243).
    supported_by:
    - reference_id: PMID:26705243
      supporting_text: The four classical small HSPs (HSP22, HSP23, HSP26, and HSP27) were all highly induced after a heat shock
    - reference_id: file:DROME/Hsp23/Hsp23-deep-research-falcon.md
      supporting_text: |-
        heat shock factor (**HSF**) is reported to bind tightly to the **Hsp23 promoter** after heat stress via heat shock elements
    additional_reference_ids:
    - file:DROME/Hsp23/Hsp23-deep-research-falcon.md
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: IBA annotation for protein refolding. sHSPs do not themselves refold proteins; they are holdases that maintain substrates in a refoldable state for subsequent HSP70-dependent refolding (PMID:16572729, PMID:26705243). The refolding capacity of sHSPs is partially dependent on an intact HSP70 machine (PMID:26705243). The IBA annotation captures the involvement of sHSPs in the refolding pathway.
    action: ACCEPT
    reason: Although Hsp23 is primarily a holdase, it participates in the protein refolding pathway by maintaining substrates in a refoldable state. In the in vitro refolding assay, 30% of luciferase activity was recovered in the presence of Hsp23 (PMID:16572729).
    supported_by:
    - reference_id: PMID:16572729
      supporting_text: more than 50% of luciferase activity was recovered when heat denaturation was performed in the presence of Hsp22, 40% with Hsp27, and 30% with Hsp23 or Hsp26
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: IBA annotation for unfolded protein binding. GO:0051082 is proposed for obsoletion. sHSPs are classic holdases that bind unfolded/denatured proteins and prevent their aggregation in an ATP-independent manner (PMID:16572729). As holdases, the closest replacement term is GO:0140309 (unfolded protein carrier activity).
    action: MODIFY
    reason: GO:0051082 is proposed for obsoletion. As a holdase, Hsp23 prevents aggregation of unfolded proteins (PMID:16572729). GO:0140309 (unfolded protein carrier activity) is not appropriate because it is carrier-specific (per go-ontology#30552). Retain until a holdase chaperone activity NTR is created.
    proposed_replacement_terms:
    - id: GO:0051082
      label: unfolded protein binding (retain until holdase NTR is created)
    supported_by:
    - reference_id: file:DROME/Hsp23/Hsp23-deep-research-falcon.md
      supporting_text: |-
        a key mechanistic distinction emphasized in Drosophila-focused reviews is that sHSPs can **prevent nonspecific protein aggregation in an ATP‑independent manner**
    additional_reference_ids:
    - file:DROME/Hsp23/Hsp23-deep-research-falcon.md
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: IEA annotation from ARBA for cytoplasm localization. Consistent with IBA and IDA annotations for cytoplasm/cytosol. Redundant with better-evidenced annotations.
    action: ACCEPT
    reason: This IEA annotation is consistent with the IBA and experimental (IDA cytosol) annotations. Acceptable as redundant support.
- term:
    id: GO:0009408
    label: response to heat
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: IEA annotation from ARBA for response to heat. Consistent with IBA and IDA annotations for the same term.
    action: ACCEPT
    reason: This IEA annotation is consistent with the IDA and IBA annotations for the same term. Acceptable as redundant support.
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: IEA annotation from ARBA for protein refolding. Consistent with IBA and IDA annotations.
    action: ACCEPT
    reason: This IEA annotation is consistent with the IDA and IBA annotations for the same term. Acceptable as redundant support.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: IEA annotation from ARBA for unfolded protein binding. GO:0051082 is proposed for obsoletion. Same recommendation as for the IBA annotation.
    action: MODIFY
    reason: GO:0051082 is proposed for obsoletion. As a holdase, Hsp23 binds unfolded proteins and prevents their aggregation. GO:0140309 (unfolded protein holdase activity) is not appropriate because it is carrier-specific (escorting between cellular components, per go-ontology#30552), which does not describe in-situ holdase activity. Retain GO:0051082 until a holdase chaperone activity NTR is created, consistent with the IBA annotation.
    proposed_replacement_terms:
    - id: GO:0051082
      label: unfolded protein binding (retain until holdase NTR is created)
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:38944040
  review:
    summary: IPI annotation for protein binding from a large-scale Drosophila interactome study. The with/from column indicates interaction with P02517 (Hsp26). This interaction is independently confirmed by co-immunoprecipitation (PMID:32437379). However, protein binding is uninformative; the interaction with Hsp26 should be captured more specifically.
    action: ACCEPT
    reason: The interaction between Hsp23 and Hsp26 is well-documented by co-immunoprecipitation (PMID:32437379) and large-scale interactomics (PMID:38944040). While protein binding is uninformative as a GO term, the IPI evidence with a specific interactor is acceptable and the interaction is biologically meaningful for sHSP oligomerization.
    supported_by:
    - reference_id: PMID:32437379
      supporting_text: These results confirm the physical interaction between sHSP23 and sHSP26
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IDA
  original_reference_id: PMID:16572729
  review:
    summary: IDA annotation for protein folding based on Morrow et al. 2006 demonstrating chaperone-like activity. All four Drosophila sHSPs prevent heat-induced protein aggregation and maintain proteins in a refoldable state (PMID:16572729).
    action: ACCEPT
    reason: Hsp23 has demonstrated chaperone-like activity in preventing heat-induced protein aggregation and maintaining substrates in a refoldable state (PMID:16572729). Protein folding is an appropriate broad process annotation for a chaperone.
    supported_by:
    - reference_id: PMID:16572729
      supporting_text: Therefore, the 4 main sHsps of Drosophila share the ability to prevent heat-induced protein aggregation and are able to maintain proteins in a refoldable state, although with different efficiencies
    - reference_id: file:DROME/Hsp23/Hsp23-deep-research-falcon.md
      supporting_text: |-
        frame Hsp23 as part of the **ATP-independent sHSP chaperone system** that buffers proteotoxic stress by limiting aggregation and helping maintain protein homeostasis
    additional_reference_ids:
    - file:DROME/Hsp23/Hsp23-deep-research-falcon.md
- term:
    id: GO:0044183
    label: protein folding chaperone
  evidence_type: IDA
  original_reference_id: PMID:16572729
  review:
    summary: IDA annotation for protein folding chaperone. Morrow et al. (2006) demonstrated that Hsp23 has chaperone-like activity, though less efficient than Hsp22 or Hsp27, requiring a 5-fold molar excess for equivalent anti-aggregation. However, GO:0044183 is defined as an ATP-dependent protein folding chaperone (foldase), which does not accurately describe sHSPs that function as ATP-independent holdases.
    action: MODIFY
    reason: GO:0044183 (protein folding chaperone) is for foldases (ATP-dependent). Hsp23 is an ATP-independent holdase requiring HSP70 for actual refolding (PMID:26705243); Drosophila sHSP reviews reiterate that sHSPs prevent aggregation in an ATP-independent manner (file:DROME/Hsp23/Hsp23-deep-research-falcon.md). The correct replacement is GO:0051082 (unfolded protein binding / holdase activity). GO:0140309 (unfolded protein holdase activity) is not appropriate because it is carrier-specific (escorting between cellular components, per go-ontology#30552), which does not describe in-situ holdase activity. Retain GO:0051082 until a holdase chaperone activity NTR is created, consistent with the IBA annotation.
    proposed_replacement_terms:
    - id: GO:0051082
      label: unfolded protein binding (retain until holdase NTR is created)
    supported_by:
    - reference_id: PMID:16572729
      supporting_text: A 5 M excess of Hsp23 and Hsp26 was required to obtain the same efficiency with either citrate synthase or luciferase as substrate
    - reference_id: PMID:26705243
      supporting_text: the refolding capacity of D. melanogaster HSP27 and CG14207 is partially dependent on an intact HSP70 machine
    - reference_id: file:DROME/Hsp23/Hsp23-deep-research-falcon.md
      supporting_text: |-
        a key mechanistic distinction emphasized in Drosophila-focused reviews is that sHSPs can **prevent nonspecific protein aggregation in an ATP‑independent manner**
    additional_reference_ids:
    - file:DROME/Hsp23/Hsp23-deep-research-falcon.md
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: PMID:32437379
  review:
    summary: IDA annotation for cytosol localization based on Santana et al. (2020). Immunofluorescence in third instar larval brain shows that sHSP23 and sHSP26 localize in the cytoplasm of CNS cells (PMID:32437379). The more specific cytosol annotation is appropriate.
    action: ACCEPT
    reason: Direct experimental evidence from immunofluorescence shows cytoplasmic localization of Hsp23 in CNS cells (PMID:32437379). Cytosol is an appropriate specific term.
    supported_by:
    - reference_id: PMID:32437379
      supporting_text: The data show that sHSP23 and sHSP26 localize in the cytoplasm of CNS cells, in particular in the optic lobes and the central nerve cord
    - reference_id: file:DROME/Hsp23/Hsp23-deep-research-falcon.md
      supporting_text: |-
        sHsp23 is observed in **CNS cytoplasm** and to **concentrate at NMJ synaptic boutons** together with sHsp26
    additional_reference_ids:
    - file:DROME/Hsp23/Hsp23-deep-research-falcon.md
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: ISM
  original_reference_id: PMID:19715580
  review:
    summary: ISM annotation for protein folding based on sequence model analysis. Li et al. (2009) performed comparative analysis of sHSP genes across insects, identifying conserved alpha-crystallin domains characteristic of chaperone function.
    action: ACCEPT
    reason: The ISM evidence from comparative genomic analysis is consistent with experimental evidence (PMID:16572729) demonstrating chaperone activity.
    supported_by:
    - reference_id: PMID:19715580
      supporting_text: sHSPs primarily have chaperone activity and reflect the response machine of organisms to some extreme stresses existing in environment
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IDA
  original_reference_id: PMID:16572729
  review:
    summary: IDA annotation for unfolded protein binding. GO:0051082 is proposed for obsoletion. Morrow et al. (2006) demonstrated that all four sHSPs bind denatured substrates, with Hsp23 requiring a 5-fold molar excess for efficient binding.
    action: MODIFY
    reason: GO:0051082 is proposed for obsoletion. The experimental evidence clearly demonstrates holdase activity (binding denatured substrates and preventing aggregation). GO:0140309 (unfolded protein holdase activity) is not appropriate because it is carrier-specific (escorting between cellular components, per go-ontology#30552), which does not describe in-situ holdase activity. Retain GO:0051082 until a holdase chaperone activity NTR is created, consistent with the IBA annotation.
    proposed_replacement_terms:
    - id: GO:0051082
      label: unfolded protein binding (retain until holdase NTR is created)
    supported_by:
    - reference_id: PMID:16572729
      supporting_text: A 5 M excess of Hsp23 and Hsp26 was required to obtain the same efficiency with either citrate synthase or luciferase as substrate
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: ISM
  original_reference_id: PMID:19715580
  review:
    summary: ISM annotation for unfolded protein binding from comparative sHSP genomics. GO:0051082 is proposed for obsoletion.
    action: MODIFY
    reason: GO:0051082 is proposed for obsoletion. As a holdase, Hsp23 binds unfolded proteins and prevents their thermal aggregation. GO:0140309 (unfolded protein holdase activity) is not appropriate because it is carrier-specific (escorting between cellular components, per go-ontology#30552), which does not describe in-situ holdase activity. Retain GO:0051082 until a holdase chaperone activity NTR is created, consistent with the IBA annotation.
    proposed_replacement_terms:
    - id: GO:0051082
      label: unfolded protein binding (retain until holdase NTR is created)
    supported_by:
    - reference_id: PMID:19715580
      supporting_text: This stable multimeric structure formed by sHSPs has the function of molecular chaperone, which binds to the proteins and prevents them from thermal denaturation
- term:
    id: GO:0009408
    label: response to heat
  evidence_type: IDA
  original_reference_id: PMID:26705243
  review:
    summary: IDA annotation for response to heat from Vos et al. (2016). This study confirmed that the four classical sHSPs are all highly heat-inducible by qPCR in S2 cells.
    action: ACCEPT
    reason: Strongly supported by experimental evidence. Hsp23 is one of the most abundantly constitutively expressed sHSPs and is highly heat-inducible (PMID:26705243).
    supported_by:
    - reference_id: PMID:26705243
      supporting_text: The four classical small HSPs (HSP22, HSP23, HSP26, and HSP27) were all highly induced after a heat shock
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IDA
  original_reference_id: PMID:26705243
  review:
    summary: IDA annotation for protein refolding from Vos et al. (2016). In cell-based luciferase refolding assays, overexpression of the classical sHSPs (HSP23, HSP26, HSP27) increased luciferase refolding in S2 cells (PMID:26705243).
    action: ACCEPT
    reason: Cellular refolding assay confirms that Hsp23 overexpression enhances luciferase refolding. The refolding capacity requires HSP70 (PMID:26705243).
    supported_by:
    - reference_id: PMID:26705243
      supporting_text: overexpression of the classical small HSPs (HSP23, HSP26, and HSP27) increased luciferase refolding
- term:
    id: GO:0009631
    label: cold acclimation
  evidence_type: IEP
  original_reference_id: PMID:16313561
  review:
    summary: IEP annotation for cold acclimation. Qin et al. (2005) used microarray analysis to examine transcript changes during cold hardening in Drosophila. Hsp23 was identified among the stress proteins differentially expressed during cold hardening treatment. IEP (inferred from expression pattern) is appropriate for transcript upregulation data.
    action: KEEP_AS_NON_CORE
    reason: Cold acclimation is a stress response that may involve sHSP chaperone activity but represents a pleiotropic environmental response rather than a core molecular function. The IEP evidence (transcript upregulation) is relatively weak.
    supported_by:
    - reference_id: PMID:16313561
      supporting_text: stress proteins, including Hsp23, Hsp26, Hsp83 and Frost as well as membrane-associated proteins may contribute to the cold hardening response
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:9514881
  review:
    summary: IPI annotation for protein binding based on Joanisse et al. (1998). The with/from column indicates interaction with FB:FBgn0010602 (DmUbc9, the SUMO-conjugating enzyme). This was demonstrated by yeast two-hybrid and confirmed by co-immunoprecipitation.
    action: ACCEPT
    reason: The interaction between Hsp23 and DmUbc9 is experimentally validated by both yeast two-hybrid and co-immunoprecipitation (PMID:9514881). While protein binding is uninformative, the IPI evidence documents a specific interactor.
    supported_by:
    - reference_id: PMID:9514881
      supporting_text: a Drosophila melanogaster homologue of yeast and human ubc9 (Dmubc9) was found to interact with Drosophila Hsp23
- term:
    id: GO:0001666
    label: response to hypoxia
  evidence_type: IEP
  original_reference_id: PMID:19401761
  review:
    summary: IEP annotation for response to hypoxia. Azad et al. (2009) showed by microarray and qPCR that Hsp23 is significantly upregulated during constant hypoxia in Drosophila.
    action: KEEP_AS_NON_CORE
    reason: Hypoxia response is a stress response that involves sHSP chaperone activity but is a pleiotropic response rather than a core molecular function. The IEP evidence (transcript upregulation) supports involvement but not direct participation.
    supported_by:
    - reference_id: PMID:19401761
      supporting_text: Heat shock proteins up-regulation (specifically Hsp23 and Hsp70) led to a significant increase in adult survival (as compared to controls) of P-element lines during CH
- term:
    id: GO:0001666
    label: response to hypoxia
  evidence_type: IMP
  original_reference_id: PMID:19401761
  review:
    summary: IMP annotation for response to hypoxia. Azad et al. (2009) showed that Hsp23 P-element lines with increased expression had significantly higher survival under constant hypoxia (55% survival vs 31% for controls). This functional evidence goes beyond expression data.
    action: KEEP_AS_NON_CORE
    reason: The IMP evidence demonstrates a functional role for Hsp23 in hypoxia tolerance via increased survival of P-element lines. However, this represents a pleiotropic stress response phenotype rather than a core evolved function of Hsp23.
    supported_by:
    - reference_id: PMID:19401761
      supporting_text: Heat shock proteins up-regulation (specifically Hsp23 and Hsp70) led to a significant increase in adult survival (as compared to controls) of P-element lines during CH
references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: PMID:9514881
  title: Cloning and developmental expression of a nuclear ubiquitin-conjugating enzyme (DmUbc9) that interacts with small heat shock proteins in Drosophila melanogaster.
  findings:
  - statement: DmUbc9 interacts with Hsp23 in yeast two-hybrid and co-immunoprecipitation assays.
    supporting_text: "In a two hybrid screen designed to identify proteins that interact with small heat shock proteins (sHsps), a Drosophila melanogaster homologue of yeast and human ubc9 (Dmubc9) was found to interact with Drosophila Hsp23"
- id: PMID:16313561
  title: Cold hardening and transcriptional change in Drosophila melanogaster.
  findings:
  - statement: Hsp23 is among stress proteins differentially expressed during cold hardening treatment.
    supporting_text: "Taken together, these assays suggest that stress proteins, including Hsp23, Hsp26, Hsp83 and Frost as well as membrane-associated proteins may contribute to the cold hardening response."
- id: PMID:16572729
  title: Differences in the chaperone-like activities of the four main small heat shock proteins of Drosophila melanogaster.
  findings:
  - statement: All four sHSPs have chaperone-like activity; Hsp23 requires 5-fold molar excess for equivalent efficiency.
    supporting_text: "A 5 M excess of Hsp23 and Hsp26 was required to obtain the same efficiency with either citrate synthase or luciferase as substrate."
  - statement: Approximately 30% of luciferase activity is recovered with Hsp23 in refolding assays.
    supporting_text: "In an in vitro refolding assay with reticulocyte lysate, more than 50% of luciferase activity was recovered when heat denaturation was performed in the presence of Hsp22, 40% with Hsp27, and 30% with Hsp23 or Hsp26."
- id: PMID:19401761
  title: Distinct mechanisms underlying tolerance to intermittent and constant hypoxia in Drosophila melanogaster.
  findings:
  - statement: Hsp23 is upregulated during constant hypoxia; P-element lines show increased survival.
    supporting_text: "Heat shock proteins up-regulation (specifically Hsp23 and Hsp70) led to a significant increase in adult survival (as compared to controls) of P-element lines during CH."
- id: PMID:19715580
  title: The small heat shock protein (sHSP) genes in the silkworm, Bombyx mori, and comparative analysis with other insect sHSP genes.
  findings:
  - statement: Comparative analysis identifies conserved alpha-crystallin domains across insect sHSPs.
    supporting_text: "The sHSPs have an α-crystalling domain comprising about 100 amino acid residues, which is the conserved structure of all sHSP sequences [6-8]"
- id: PMID:26705243
  title: Specific protein homeostatic functions of small heat-shock proteins increase lifespan.
  findings:
  - statement: Hsp23 assists in HSP70-dependent refolding of luciferase in S2 cell-based assays.
    supporting_text: "Consistent with in vitro data (Morrow et al., 2006), overexpression of the classical small HSPs (HSP23, HSP26, and HSP27) increased luciferase refolding (Fig"
  - statement: All four classical sHSPs are highly heat-inducible.
    supporting_text: "The four classical small HSPs (HSP22, HSP23, HSP26, and HSP27) were all highly induced after a heat shock (Fig"
- id: PMID:32437379
  title: Small heat shock proteins determine synapse number and neuronal activity during development.
  findings:
  - statement: Hsp23 and Hsp26 colocalize in the cytoplasm of CNS cells and physically interact.
    supporting_text: "The data show that sHSP23 and sHSP26 localize in the cytoplasm of CNS cells, in particular in the optic lobes and the central nerve cord (Fig 2A and 2B`)"
  - statement: Hsp23 and Hsp26 modulate synapse number during development.
    supporting_text: "we suggest that sHSP23 and sHSP26 together form a complex that promotes synapse formation in presynaptic neurons, Pkm is an anti-synaptogenic element in neurons through, but not restricted to, the modulation of sHsp23 and sHsp26 (Fig 5C)."
- id: PMID:38944040
  title: Next-generation Drosophila protein interactome map and its functional implications.
  findings:
  - statement: Large-scale interactome confirms Hsp23-Hsp26 physical interaction.
    supporting_text: "The network contains 32,668 interactions among 3,644 proteins, organized into 632 clusters representing putative functional modules"
- id: file:DROME/Hsp23/Hsp23-deep-research-falcon.md
  title: Falcon deep research report on Hsp23 (Drosophila melanogaster)
  findings:
  - statement: |
      Hsp23 is a cytosolic small heat shock protein (HSP20/sHSP family) of Drosophila melanogaster (CG4463; UniProt P02516) containing the conserved alpha-crystallin domain, clustered with Hsp22, Hsp26 and Hsp27 at locus 67B; it is ~20.6 kDa and cytosolic.
    supporting_text: |-
      Hsp23 is one of the canonical sHSPs (clustered with other sHSP genes at cytological position **67B**) and is described as a ~**20.6 kDa** cytosolic protein
    reference_section_type: OTHER
  - statement: |
      As an sHSP, Hsp23 acts as an ATP-independent molecular chaperone (holdase) that prevents nonspecific protein aggregation, functioning within the proteostasis network.
    supporting_text: |-
      a key mechanistic distinction emphasized in Drosophila-focused reviews is that sHSPs can **prevent nonspecific protein aggregation in an ATP‑independent manner**
    reference_section_type: OTHER
  - statement: |
      Beyond generic chaperoning, Hsp23 is reported to bind cytoskeletal elements (actin and microtubules) and is linked to embryo morphogenetic processes such as ventral furrow formation.
    supporting_text: |-
      multiple syntheses cite evidence that Hsp23 can **bind cytoskeletal elements** (including **actin and microtubules**) and has been linked to **embryo morphogenetic processes**
    reference_section_type: OTHER
  - statement: |
      Hsp23 is a cytoplasmic/cytosolic sHSP, in contrast to the mitochondrial Hsp22; in the nervous system it localizes to CNS cytoplasm and concentrates at NMJ synaptic boutons together with sHsp26.
    supporting_text: |-
      sHsp23 is observed in **CNS cytoplasm** and to **concentrate at NMJ synaptic boutons** together with sHsp26
    reference_section_type: OTHER
  - statement: |
      Hsp23 transcription is regulated by the canonical heat-shock response (HSF binds the Hsp23 promoter via heat shock elements after heat stress), by dFOXO during oxidative stress, and by ecdysone during development.
    supporting_text: |-
      heat shock factor (**HSF**) is reported to bind tightly to the **Hsp23 promoter** after heat stress via heat shock elements
    reference_section_type: OTHER
  - statement: |
      dFOXO directly targets multiple inducible sHSP promoters including Hsp23, placing Hsp23 at the intersection of oxidative stress and proteostasis regulation.
    supporting_text: |-
      A mechanistic study of oxidative-stress transcriptional control in Drosophila reports that **dFOXO directly targets multiple sHSP promoters including Hsp23**
    reference_section_type: OTHER
  - statement: |
      Muscle-specific Hsp23 overexpression protects flight muscle against heat-stress-induced degeneration with both cell-autonomous and cell-nonautonomous (neuron/glia) protection, whereas Hsp70 overexpression does not protect in the same paradigm.
    supporting_text: |-
      **Muscle-specific Hsp23 overexpression** protects flight muscle and also provides **cell-nonautonomous protection** of motor neurons and glia after heat stress, whereas **Hsp70 overexpression does not** protect in the same paradigm
    reference_section_type: OTHER
  - statement: |
      Hsp23 overexpression reorganizes ubiquitinated proteins into perinuclear ring-like puncta and preserves the microtubule cytoskeleton after heat shock, linking Hsp23 to stress-resilient proteostasis and cytoskeletal integrity.
    supporting_text: |-
      Hsp23 overexpression is associated with **organized perinuclear ubiquitin puncta** and preservation of the **microtubule cytoskeleton** following heat shock
    reference_section_type: OTHER
  - statement: |
      In developing motor neurons, excess sHsp23 reduces synapse number (active zones per NMJ) and is not required for synapse formation, indicating dosage-sensitive effects on synapse development.
    supporting_text: |-
      In motor neurons, sHsp23 overexpression is reported to **reduce synapse number** (as quantified by active zones per NMJ) and is interpreted as **not required for synapse formation**
    reference_section_type: OTHER
  - statement: |
      Maternal loading/overexpression of Hsp23 in oocytes increases thermal tolerance of offspring embryos and improves larval performance, supporting a thermoprotective role during early development.
    supporting_text: |-
      developmental review evidence further indicates that **maternal loading/overexpression of Hsp23 in oocytes increases thermal tolerance of offspring embryos** and improves larval performance
    reference_section_type: OTHER
core_functions:
- molecular_function:
    id: GO:0051082
    label: unfolded protein binding
  description: Hsp23 functions as an ATP-independent holdase chaperone that prevents heat-induced protein aggregation and maintains substrates in a refoldable state. Less efficient than Hsp22 or Hsp27, requiring a 5-fold molar excess for equivalent anti-aggregation activity (PMID:16572729). Refolding of substrates held by Hsp23 requires the HSP70 machine (PMID:26705243). Hsp23 physically interacts with Hsp26, and both proteins colocalize in the cytoplasm of CNS cells (PMID:32437379). Note - GO:0140309 is the closest available term for holdases, though the carrier semantics do not perfectly describe in-situ holdase activity.
  locations:
  - id: GO:0005829
    label: cytosol
  directly_involved_in:
  - id: GO:0006457
    label: protein folding

Gene Description

Existing Annotations Review

Core Functions

References

Deep Research

Falcon

Research report: Drosophila melanogaster Hsp23 (CG4463; UniProt P02516) — functional annotation

0) Target verification (gene/protein identity)

1) Key concepts and definitions (current understanding)

1.1 Small heat shock proteins (sHSPs)

1.2 Hsp23 as an sHSP in Drosophila

2) Molecular function and mechanism

2.1 Primary molecular function: ATP-independent chaperone/proteostasis factor

2.2 Cytoskeletal association and morphogenesis

3) Subcellular localization (where it acts)

3.1 Predominantly cytosolic/cytoplasmic

3.2 CNS and synapse-associated localization

3.3 Perinuclear proteostasis-associated organization in muscle under heat stress

4) Regulation and pathway context

4.1 Canonical heat shock response: HSF → Hsp23

4.2 Oxidative stress/insulin signaling axis: dFOXO → Hsp23

4.3 Developmental hormone regulation and chromatin features

5) Biological roles: development, stress tolerance, and aging

5.1 Developmental/tissue expression

5.2 Germline/ovary isoforms and maternal effects

5.3 Aging-associated induction

6) Perturbation phenotypes and functional studies (experimental evidence)

6.1 Flight muscle proteostasis and degeneration protection (heat stress model)

6.2 Synapse number and neuronal activity (developmental context)

6.3 Loss-of-function/essentiality and redundancy

7) Recent developments and latest research (2023–2024 prioritized)

7.1 2023: pharmacologic TOR pathway modulation alters Hsp23 among chaperones in fly CNS

7.2 2024: nuclear/cytoskeletal factors modulate heat shock gene expression including Hsp23 (metadata-level)

8) Current applications and real-world implementations

9) Expert opinions and authoritative synthesis (interpretive analysis)

10) Key statistics and data points (from retrieved sources)

11) Visual evidence from primary literature (figures)

12) Evidence summary table

13) Gaps and recommendations for further annotation work

References (URLs and publication dates)

Artifacts

Citations

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