Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005783 endoplasmic reticulum	IBA GO_REF:0000033	ACCEPT	Summary: ERP29 is an ER-resident lumenal protein; the ER is its primary site of action. Reason: ER localization is well supported (retention signal, immunofluorescence, fractionation) and is the core compartment for ERP29's chaperone function. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.
GO:0005783 endoplasmic reticulum	IEA GO_REF:0000002	ACCEPT	Summary: Electronic ER localization, consistent with the IBA/IDA evidence. Reason: Correct compartment for this ER-resident chaperone. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.
GO:0005788 endoplasmic reticulum lumen	IEA GO_REF:0000120	ACCEPT	Summary: ERP29 is a soluble ER-lumenal protein with a KEEL retention signal; the precise compartment. Reason: ER lumen is the documented, precise localization for this soluble chaperone. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.
GO:0009306 protein secretion	IEA GO_REF:0000002	KEEP AS NON CORE	Summary: ERP29 participates in the processing and secretion of secretory proteins; a plausible downstream process of its chaperone role. Reason: ERP29 facilitates secretory-protein processing/trafficking, so a protein-secretion process annotation is reasonable but is a downstream consequence of its chaperone function rather than a direct molecular activity. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt Plays an important role in the processing of secretory proteins within the endoplasmic reticulum
GO:0042470 melanosome	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: ERP29 was identified by mass spectrometry in melanosome fractions; a secondary localization. Reason: A proteomics-detected secondary localization, peripheral to the core ER-lumenal chaperone function. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt Identified by mass spectrometry in melanosome fractions
GO:0005515 protein binding	IPI PMID:23864651 The identification of novel proteins that interact with the ...	KEEP AS NON CORE	Summary: Interaction with the GLP-1 receptor (GLP1R/P43220) identified in a screen for GLP1R-interacting proteins. The bare protein binding term is uninformative. Reason: A specific interaction (GLP1R) consistent with ERP29 handling secretory/membrane clients, but the generic protein binding term is uninformative and not core. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt P30040; P43220: GLP1R; NbExp=2; IntAct=EBI-946830, EBI-7466542;
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	KEEP AS NON CORE	Summary: Reference binary interactome capturing many ERP29 interactions (e.g. SGTA, SGTB, TMBIM6, UBQLN1/2). Bare protein binding is uninformative. Reason: High-throughput binary interactions; the generic protein binding term is uninformative and not part of the core function. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt P30040; O43765: SGTA; NbExp=3; IntAct=EBI-946830, EBI-347996;
GO:0005576 extracellular region	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Extracellular/secreted pool inferred from the rat ortholog; peripheral to the ER chaperone role. Reason: A secreted pool is reported (and ERP29 is detected at the cell surface), but this is secondary to its core ER-lumenal localization. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt Melanosome.
GO:0005790 smooth endoplasmic reticulum	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Smooth-ER localization inferred from the rat ortholog; a sub-compartment refinement of the ER localization. Reason: A plausible ER sub-compartment annotation transferred by similarity; subsumed by the core ER/ER-lumen localization. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.
GO:0006888 endoplasmic reticulum to Golgi vesicle-mediated transport	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: ER-to-Golgi transport role inferred from the rat ortholog; consistent with ERP29's role in secretory-cargo trafficking. The falcon deep research corroborates a role in the early secretory pathway, with ERP29 cycling between ER and Golgi via the KDEL receptor (its weaker KEEL retention variant) to escort clients such as ENaC. Reason: A plausible downstream trafficking process inferred by similarity; non-core relative to the chaperone molecular function. The falcon deep research provides additional (unverified) support for dynamic ER-to-Golgi cycling via the KDEL receptor and a role in client forward trafficking, reinforcing the biological plausibility of this process annotation. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt Plays an important role in the processing of secretory proteins within the endoplasmic reticulum file:human/ERP29/ERP29-deep-research-falcon.md dynamic cycling between the ER and Golgi apparatus via interactions with the KDEL receptor
GO:0009725 response to hormone	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: A broad 'response to hormone' process inferred from the rat ortholog; vague and not characteristic of ERP29's molecular function. Reason: An unspecific, by-similarity process annotation with no direct human evidence and no clear connection to ERP29's chaperone function; over-annotated. Supporting Evidence: file:human/ERP29/ERP29-goa.tsv GO:0009725
GO:0009986 cell surface	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Cell-surface localization inferred from the mouse ortholog; corroborated by direct evidence in platelets, but secondary to the ER role. Reason: A genuine but minor surface pool (also IDA in platelets); peripheral to ERP29's core ER-lumenal chaperone function. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt Melanosome.
GO:0042803 protein homodimerization activity	IEA GO_REF:0000107	ACCEPT	Summary: ERP29 functions as a homodimer; homodimerization is a genuine structural property documented by UniProt and crystal structures. Reason: ERP29 is a well-documented homodimer; homodimerization activity is correct, though it is structural rather than the principal client-facing function. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt SUBUNIT: Homodimer.
GO:0051087 protein-folding chaperone binding	IEA GO_REF:0000107	ACCEPT	Summary: ERP29 binds molecular chaperones as part of a large ER chaperone complex (BiP, GRP94, PDI, ERdj3, cyclophilin B, ERp72, etc.) and, per the falcon deep research, is recruited to the calnexin/calreticulin (CNX/CRT) lectin-chaperone cycle, with its C-terminal D domain serving as the binding interface for the CNX/CRT P domains; chaperone binding is central to its escort function. Reason: ERP29's participation in the ER chaperone multiprotein complex is experimentally documented; protein-folding chaperone binding is an informative, core molecular function. The falcon deep research adds a specific mechanistic basis - ERP29 is recruited as a function-specific co-chaperone within the calnexin/calreticulin cycle via direct binding of its D domain to the CNX/CRT P domains - consistent with this chaperone-binding annotation (these CNX/CRT-cycle citations were not independently verified against cached publications). Supporting Evidence: PMID:12475965 large endoplasmic reticulum (ER)-localized multiprotein complex that is comprised of the molecular chaperones BiP file:human/ERP29/ERP29-deep-research-falcon.md C-terminal D domain serves as the principal binding interface for lectin chaperones in the calnexin/calreticulin system
GO:1902235 regulation of endoplasmic reticulum stress-induced intrinsic apoptotic signaling pathway	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: A role in regulating ER-stress-induced apoptosis inferred from the mouse ortholog; consistent with ERP29's ER-stress-related functions but indirect. The falcon deep research reports human-cell evidence (RPE cells) that ERP29 overexpression raises protective stress proteins (GRP78, p58IPK, Nrf2) and lowers pro-apoptotic CHOP, supporting a protective modulation of ER-stress-induced apoptotic signaling. Reason: A plausible context-specific process inferred by similarity; non-core relative to the chaperone molecular function. The falcon deep research adds (unverified) supportive evidence that ERP29 attenuates ER stress and shifts the balance away from CHOP-driven apoptosis, consistent with this regulatory annotation though still peripheral to its core chaperone-binding function. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt Plays an important role in the processing of secretory proteins within the endoplasmic reticulum file:human/ERP29/ERP29-deep-research-falcon.md increased levels of protective stress response proteins including GRP78, p58IPK, and Nrf2, while reducing pro-apoptotic markers phospho-eIF2α and CHOP
GO:0043410 positive regulation of MAPK cascade	IDA PMID:22064321 ERp29 induces breast cancer cell growth arrest and survival ...	KEEP AS NON CORE	Summary: In breast cancer cells, ERP29 overexpression activates p38 MAPK and induces growth arrest; a cell-context-specific signaling effect. Reason: Documented in a cancer-overexpression model; a specialized downstream signaling effect rather than ERP29's core ER chaperone function. Supporting Evidence: PMID:22064321 ERp29-induced cancer cell growth arrest is modulated by the interplay between the concomitant phosphorylation of p38
GO:0005790 smooth endoplasmic reticulum	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS smooth-ER localization (rat ortholog); a sub-compartment refinement. Reason: Redundant with the IEA smooth-ER annotation; subsumed by the core ER/ER-lumen localization. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.
GO:0051087 protein-folding chaperone binding	ISS GO_REF:0000024	ACCEPT	Summary: ISS protein-folding chaperone binding (rat ortholog), consistent with ERP29's role in the ER chaperone complex. Reason: Corroborates the experimentally supported chaperone-binding function (ER chaperone complex membership); an informative core molecular function. Supporting Evidence: PMID:12475965 large endoplasmic reticulum (ER)-localized multiprotein complex that is comprised of the molecular chaperones BiP
GO:0003756 protein disulfide isomerase activity	IKR NOT PMID:9738895 ERp28, a human endoplasmic-reticulum-lumenal protein, is a m...	ACCEPT	Summary: This is a NOT (negated) annotation - ERP29 does NOT have protein disulfide isomerase activity, because it lacks the CXXC thioredoxin-box motif. The negation is correct. Reason: Directly supported - ERP29 lacks the CXXC (CGHC) active-site motif and is not a disulfide isomerase; the NOT annotation correctly blocks transfer of isomerase activity. The falcon deep research independently affirms the redox-inactive, non-catalytic nature of ERP29 (lacks the CXXC catalytic motif; functions as a chaperone, not a catalyst). Supporting Evidence: PMID:9738895 member of the protein disulfide isomerase family but lacks a CXXC thioredoxin-box motif file:human/ERP29/ERP29-deep-research-falcon.md lacks the characteristic CXXC catalytic motif file:human/ERP29/ERP29-deep-research-falcon.md establishing its primary role as a chaperone rather than a catalyst
GO:0005783 endoplasmic reticulum	IDA PMID:9738895 ERp28, a human endoplasmic-reticulum-lumenal protein, is a m...	ACCEPT	Summary: Direct evidence (fractionation and immunofluorescence) for ER localization. Reason: IDA-supported ER localization from the founding characterization. Supporting Evidence: PMID:9738895 localizes to the endoplasmic reticulum (ER) as seen by subcellular fractionation and immunofluorescence studies
GO:0005788 endoplasmic reticulum lumen	NAS PMID:22064321 ERp29 induces breast cancer cell growth arrest and survival ...	ACCEPT	Summary: ER-lumen localization asserted in the literature; correct and core. Reason: ERP29 is a soluble ER-lumenal protein; consistent with its retention signal and direct localization data. Supporting Evidence: PMID:22064321 ERp29) is an ER luminal protein
GO:0006457 protein folding	NAS PMID:9738895 ERp28, a human endoplasmic-reticulum-lumenal protein, is a m...	KEEP AS NON CORE	Summary: ERP29 may participate in folding of secretory proteins as a non-catalytic chaperone; protein folding is a plausible downstream process. Reason: ERP29 assists folding indirectly as an escort/chaperone (it is not a foldase); protein folding is a non-core process annotation. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt possibly by participating in the folding of proteins in the ER
GO:0006886 intracellular protein transport	NAS PMID:9738895 ERp28, a human endoplasmic-reticulum-lumenal protein, is a m...	KEEP AS NON CORE	Summary: ERP29 participates in the trafficking/processing of secretory proteins; intracellular protein transport is a plausible downstream process. Reason: A reasonable downstream process consequence of ERP29's escort/chaperone role; non-core relative to its molecular function. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt Plays an important role in the processing of secretory proteins within the endoplasmic reticulum
GO:0010628 positive regulation of gene expression	IDA PMID:22064321 ERp29 induces breast cancer cell growth arrest and survival ...	KEEP AS NON CORE	Summary: In a breast-cancer overexpression model, ERP29 modulates gene expression (e.g. upregulation of p58IPK); a context-specific downstream effect. Reason: A specialized, cell-context-specific transcriptional effect from an overexpression study; not ERP29's core ER chaperone function. Supporting Evidence: PMID:22064321 upregulation of the inhibitor of the interferon-induced, double-stranded RNA-activated protein kinase, p58(IPK)
GO:0010629 negative regulation of gene expression	IDA PMID:22064321 ERp29 induces breast cancer cell growth arrest and survival ...	KEEP AS NON CORE	Summary: ERP29 also negatively regulates expression of certain genes in the cancer-cell model; a context-specific downstream effect. Reason: A specialized transcriptional effect in an overexpression model; non-core relative to the chaperone function. Supporting Evidence: PMID:22064321 ERp29-induced cancer cell growth arrest
GO:0043335 protein unfolding	NAS PMID:22064321 ERp29 induces breast cancer cell growth arrest and survival ...	KEEP AS NON CORE	Summary: ERP29 has been proposed to have a protein-unfolding activity (e.g. in toxin/virus membrane penetration); asserted in the literature but mechanistically limited. Reason: A proposed specialized activity (substrate unfolding/local conformational change) rather than ERP29's principal chaperone-binding function; retained as non-core. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt a role in protein unfolding and secretion
GO:0050709 negative regulation of protein secretion	IDA PMID:22064321 ERp29 induces breast cancer cell growth arrest and survival ...	KEEP AS NON CORE	Summary: ERP29 overexpression can negatively regulate secretion of specific proteins in the cancer model; a context-specific effect. Reason: A specialized, context-dependent secretion-regulation effect; non-core relative to the chaperone function. Supporting Evidence: PMID:22064321 ERp29) is an ER luminal protein that has a role in protein unfolding and secretion
GO:0016020 membrane	HDA PMID:19946888 Defining the membrane proteome of NK cells.	KEEP AS NON CORE	Summary: High-throughput membrane-proteome detection; generic and uninformative for this soluble ER-lumenal protein (likely reflects ER-membrane-associated complexes or surface pool). Reason: A generic proteomic localization; uninformative relative to the precise ER-lumen localization. Supporting Evidence: file:human/ERP29/ERP29-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.
GO:0009986 cell surface	IDA PMID:19995400 Platelets release novel thiol isomerase enzymes which are re...	KEEP AS NON CORE	Summary: Direct evidence that ERP29 (a thiol-isomerase-family protein) is released by platelets and recruited to the cell surface upon activation; a genuine but specialized surface pool. Reason: A real activation-dependent surface pool in platelets, but peripheral to ERP29's core ER-lumenal chaperone function. Supporting Evidence: PMID:19995400 Platelets release novel thiol isomerase enzymes which are recruited to the cell surface following activation

Core Functions

Non-catalytic, ER-lumenal escort/chaperone of the PDI family (lacking a CXXC active site) that assists the folding, processing and trafficking of secretory cargo by binding molecular chaperones within a large ER chaperone multiprotein complex.

Molecular Function:

protein-folding chaperone binding

Cellular Locations:

endoplasmic reticulum lumen

Supporting Evidence:

PMID:12475965
large endoplasmic reticulum (ER)-localized multiprotein complex that is comprised of the molecular chaperones BiP
file:human/ERP29/ERP29-uniprot.txt
Plays an important role in the processing of secretory proteins within the endoplasmic reticulum

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000024

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000044

Gene Ontology annotation based on UniProtKB Subcellular Location vocabulary mapping

GO_REF:0000107

Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:9738895

ERp28, a human endoplasmic-reticulum-lumenal protein, is a member of the protein disulfide isomerase family but lacks a CXXC thioredoxin-box motif.

ERp28/ERp29 is an ER-lumenal protein with a KEEL retention signal that is a PDI-family member but lacks the CXXC (CGHC) thioredoxin-box motif, hence is not a disulfide isomerase.

PMID:12475965

A subset of chaperones and folding enzymes form multiprotein complexes in endoplasmic reticulum to bind nascent proteins.

ERp29 is part of a large ER chaperone multiprotein complex (BiP, GRP94, PDI, ERdj3, cyclophilin B, ERp72, GRP170, UGGT, SDF2-L1) that binds unassembled, incompletely folded immunoglobulin heavy chains.

PMID:19946888

Defining the membrane proteome of NK cells.

PMID:19995400

Platelets release novel thiol isomerase enzymes which are recruited to the cell surface following activation.

ERP29 is among thiol-isomerase-family proteins released by platelets and recruited to the platelet surface following activation.

PMID:22064321

ERp29 induces breast cancer cell growth arrest and survival through modulation of activation of p38 and upregulation of ER stress protein p58IPK.

In breast cancer cells, ERp29 (an ER luminal protein with a role in protein unfolding and secretion) overexpression induces growth arrest via p38 MAPK activation and upregulation of p58IPK, modulating gene expression and protein secretion.

PMID:23864651

The identification of novel proteins that interact with the GLP-1 receptor and restrain its activity.

PMID:32296183

A reference map of the human binary protein interactome.

file:human/ERP29/ERP29-uniprot.txt

UniProt entry P30040 (ERP29_HUMAN), Endoplasmic reticulum resident protein 29

Non-catalytic (no CXXC) PDI-family ER-lumenal homodimeric chaperone that assists processing/folding of secretory proteins; part of a large ER chaperone complex; KEEL ER-retention signal; also detected in melanosomes and at the cell surface.

file:human/ERP29/ERP29-deep-research-falcon.md

Falcon deep research report for ERP29

ERP29 lacks the characteristic CXXC catalytic motif of classical PDIs and acts as a chaperone rather than a catalyst; it is recruited to the calnexin/calreticulin cycle, its C-terminal D domain being the principal interface that binds the CNX/CRT P domains, and it cycles between ER and Golgi via the KDEL receptor (KEEL motif) to assist early-secretory-pathway folding/trafficking of clients such as thyroglobulin and ENaC.

Suggested Experiments

Experiment: Reconstitute ERP29 within the ER chaperone complex and test, with defined unfolded clients, whether ERP29 modulates client binding, folding kinetics or release relative to ERP29-depleted complexes.

Experiment: ERP29 knockout/knockdown in secretory cell types followed by secretome and client-folding analysis (e.g. thyroglobulin, connexin trafficking) to define its non-redundant chaperone clients.

Deep Research

Falcon

(ERP29-deep-research-falcon.md)

Comprehensive Research Report: ERP29 Gene (UniProt P30040) - Functional Annotation Falcon Edison Scientific Literature 27 citations 1 artifacts 2026-06-20T07:08:45.815775

Edison artifact artifact-00 (text/markdown)

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.

Comprehensive Research Report: ERP29 Gene (UniProt P30040) - Functional Annotation

Gene Identity and Overview

The human ERP29 gene (chromosome 12, UniProt accession P30040) encodes endoplasmic reticulum resident protein 29 (ERp29), also known as ERp28, ERp31, or PDIA9 (rahman2022functionsandmechanisms pages 1-2, sakono2022erendogenousprotein pages 2-4). ERp29 is classified as a noncanonical member of the protein disulfide isomerase (PDI) family, distinguished by its lack of traditional oxidoreductase activity (powell2021proteindisulphideisomerase pages 3-4, rahman2022functionsandmechanisms pages 1-2). This 29 kDa protein is ubiquitously expressed across tissues and cell types, with particularly high abundance in secretory epithelia (huang2015erp29attenuatescigarette pages 1-2, bikard2019thekdelreceptor pages 1-2).

Category	ERp29 summary	Evidence
Protein identity and synonyms	Human ERP29 encodes endoplasmic reticulum resident protein 29; reported aliases include ERp29, ERp28, ERp31, and PDIA9. It is treated in the literature as a noncanonical member of the PDI family.	(rahman2022functionsandmechanisms pages 1-2, sakono2022erendogenousprotein pages 2-4)
Domain architecture	ERp29 contains an N-terminal thioredoxin-like domain and a C-terminal D domain unique to ERp29; the D domain is the principal interface for binding lectin chaperones in the calnexin/calreticulin system.	(kozlov2017mappingtheer pages 1-3, kozlov2017mappingtheer pages 4-5)
Key structural features	Unlike classical PDI enzymes, ERp29 lacks a functional CXXC active-site motif and is therefore not considered a typical oxidoreductase; one study/reviewed summary notes a single cysteine (Cys157) instead. ERp29 also carries a C-terminal KEEL ER-retention motif, a KDEL-like sequence linked to relatively weak ER retention and recycling through the early secretory pathway.	(bikard2019thekdelreceptor pages 1-2, sakono2022erendogenousprotein pages 2-4)
Oligomeric/structural behavior	ERp29 is described as a dimer whose N-terminal thioredoxin-like region mediates homodimerization, while the D domain forms the binding surface for partner chaperones. Structural work identified helices α8/α9 and residues including R223, L227, L241 as critical for P-domain binding.	(kozlov2017mappingtheer pages 1-3, kozlov2017mappingtheer pages 4-5, kozlov2017mappingtheer pages 5-6)
Primary molecular function	ERp29 functions primarily as an ER luminal chaperone/co-chaperone that assists folding, maturation, and trafficking of secretory and membrane proteins. Its role is best understood as general protein-folding assistance rather than catalysis of disulfide exchange.	(huang2015erp29attenuatescigarette pages 1-2, adams2021theroleof pages 1-3, sakono2022erendogenousprotein pages 2-4)
Role in calnexin/calreticulin cycle	In the calnexin/calreticulin cycle, ERp29 is recruited by the P domains of calnexin (CNX) and calreticulin (CRT) as a function-specific chaperone, alongside ERp57 and cyclophilin B, to help mature monoglucosylated glycoprotein clients.	(kozlov2017mappingtheer pages 1-3, kozlov2020calnexincycle– pages 1-3, sakono2022erendogenousprotein pages 2-4)
Binding affinity data	The ERp29 D domain binds CNX/CRT P domains with micromolar affinity; reported values are better than 20 μM by NMR for CNX and about 13 μM for full-length ERp29–CRT by surface plasmon resonance.	(kozlov2017mappingtheer pages 3-4, kozlov2017mappingtheer pages 4-5)
Known substrates / client classes	Experimentally implicated clients include thyroglobulin (folding/secretion), collagen, ENaC during channel biogenesis, and broader classes of glycoproteins handled through the calnexin/calreticulin pathway.	(kozlov2017mappingtheer pages 1-3, kozlov2020calnexincycle– pages 1-3, bikard2019thekdelreceptor pages 1-2, baryshev2004unfoldedproteinresponse pages 1-2)
Thyroglobulin-related role	ERp29 associates with thyroglobulin (Tg) in congenital hypothyroid disorders featuring ER-retained mutant Tg, supporting a role in Tg quality control and secretion.	(baryshev2004unfoldedproteinresponse pages 1-2)
ENaC-related role	ERp29 regulates epithelial sodium channel (ENaC) biogenesis; its KEEL motif and interaction with the KDEL receptor (KDEL-R) influence forward trafficking/processing during passage through the early secretory pathway.	(bikard2019thekdelreceptor pages 1-2)
Binding partners	Reported interacting or functionally associated partners include calnexin, calreticulin, ERp57, cyclophilin B (CypB), KDEL receptor, and stress/folding chaperones such as BiP/GRP78 and GRP94.	(kozlov2017mappingtheer pages 1-3, huang2015erp29attenuatescigarette pages 1-2, kozlov2020calnexincycle– pages 1-3, bikard2019thekdelreceptor pages 1-2)
Subcellular localization	ERp29 is primarily an ER lumen resident protein. Because its KEEL motif is a weaker KDEL variant, it can function dynamically in the early secretory pathway, including ER-to-Golgi trafficking steps and likely ERGIC/proximal Golgi recycling behavior.	(huang2015erp29attenuatescigarette pages 1-2, bikard2019thekdelreceptor pages 1-2, sakono2022erendogenousprotein pages 2-4)
Associated pathways	Main pathways/processes linked to ERp29 are the calnexin/calreticulin cycle, ER protein folding/quality control, unfolded protein response (UPR)/ER stress adaptation, ER-associated degradation (ERAD)-linked quality control, and protein secretion/ER-to-Golgi trafficking.	(kozlov2020calnexincycle– pages 1-3, suzuki2021foldingandquality pages 1-3, baryshev2004unfoldedproteinresponse pages 1-2)
ER stress biology	ERp29 is stress responsive and can modulate ER-stress outputs: in RPE cells, ERp29 overexpression increased GRP78, p58IPK, and Nrf2, while reducing p-eIF2α and CHOP, consistent with a protective role during ER stress.	(huang2015erp29attenuatescigarette pages 1-2)
Current functional interpretation	Overall, ERp29 is best understood as a specialized, noncatalytic PDI-family chaperone that couples client folding to lectin-chaperone recruitment and early secretory-pathway trafficking, rather than as a classical disulfide isomerase enzyme.	(kozlov2017mappingtheer pages 1-3, adams2021theroleof pages 1-3, rahman2022functionsandmechanisms pages 1-2, kozlov2020calnexincycle– pages 1-3)

Table: This table summarizes the main structural features, molecular functions, interaction partners, substrates, localization, and pathway context of human ERp29. It is useful as a compact evidence-based reference for functional annotation of ERP29.

Structural Features and Domain Organization

ERp29 possesses a distinctive bi-domain architecture comprising an N-terminal thioredoxin-like domain and a C-terminal D domain (kozlov2017mappingtheer pages 1-3, kozlov2017mappingtheer pages 4-5). Unlike classical PDI family members, ERp29 lacks the characteristic CXXC catalytic motif essential for disulfide bond formation and isomerization, containing instead only a single cysteine residue at position 157 (bikard2019thekdelreceptor pages 1-2, sakono2022erendogenousprotein pages 2-4). This structural feature fundamentally distinguishes ERp29 from oxidoreductase PDIs, establishing its primary role as a chaperone rather than a catalyst (adams2021theroleof pages 1-3, rahman2022functionsandmechanisms pages 1-2).

The N-terminal thioredoxin-like domain mediates homodimerization and binds denatured protein substrates, while the unique C-terminal D domain serves as the principal binding interface for lectin chaperones in the calnexin/calreticulin system (kozlov2017mappingtheer pages 1-3, kozlov2017mappingtheer pages 4-5). Crystal structures of the ERp29 D domain in complex with P domains from calreticulin (PDB: 5V8Z) and calmegin (PDB: 5V90) reveal that the D domain adopts an all-helical fold with two C-terminal antiparallel helices (α8 and α9) extending from a three-helix bundle (kozlov2017mappingtheer pages 3-4, kozlov2017mappingtheer pages 4-5). Key residues including R223, L227, and L241 within the D domain are critical for P-domain binding through a combination of salt bridges, hydrogen bonds, and hydrophobic interactions (kozlov2017mappingtheer pages 4-5, kozlov2017mappingtheer pages 5-6).

Subcellular Localization

ERp29 functions primarily as an endoplasmic reticulum (ER) luminal resident protein, as determined by its C-terminal KEEL retention motif—a variant of the canonical KDEL sequence (bikard2019thekdelreceptor pages 1-2, sakono2022erendogenousprotein pages 2-4). The KEEL motif provides less robust ER retention compared to KDEL, enabling dynamic cycling between the ER and Golgi apparatus via interactions with the KDEL receptor (KDEL-R) (bikard2019thekdelreceptor pages 1-2). This weaker retention mechanism allows ERp29 to escort client proteins through the early secretory pathway, including the ER-Golgi intermediate compartment (ERGIC), facilitating both protein folding assistance and quality control during trafficking (huang2015erp29attenuatescigarette pages 1-2, bikard2019thekdelreceptor pages 1-2). Bikard et al. (2019) demonstrated that the KDEL-R plays an essential role in ERp29-mediated regulation of protein biogenesis and forward trafficking, supporting a model where ERp29 dynamically associates with the ER lumen while maintaining capacity for Golgi retrieval (bikard2019thekdelreceptor pages 1-2).

Primary Molecular Functions and Substrate Specificity

Chaperone Function

ERp29 functions as a specialized ER chaperone that assists protein folding through mechanisms independent of disulfide bond catalysis (huang2015erp29attenuatescigarette pages 1-2, adams2021theroleof pages 1-3, sakono2022erendogenousprotein pages 2-4). The N-terminal thioredoxin-like domain binds misfolded or partially folded proteins, preventing aggregation and facilitating productive folding pathways (huang2015erp29attenuatescigarette pages 1-2, sakono2022erendogenousprotein pages 2-4). Multiple studies have demonstrated that ERp29 exhibits chaperone-like properties similar to classical PDIs but operates through non-catalytic mechanisms (adams2021theroleof pages 1-3, powell2021proteindisulphideisomerase pages 3-4, rahman2022functionsandmechanisms pages 1-2).

Recruitment to the Calnexin/Calreticulin Cycle

A defining feature of ERp29 function is its recruitment to the calnexin (CNX) and calreticulin (CRT) lectin chaperone system (kozlov2017mappingtheer pages 1-3, kozlov2020calnexincycle– pages 1-3, sakono2022erendogenousprotein pages 2-4). In this cycle, newly synthesized N-glycosylated proteins bearing monoglucosylated glycans (Glc₁Man₉GlcNAc₂) bind to CNX or CRT, which in turn recruit ERp29 alongside other folding factors including ERp57 (a protein disulfide isomerase) and cyclophilin B (a peptidyl-prolyl isomerase) (kozlov2020calnexincycle– pages 1-3, suzuki2021foldingandquality pages 1-3). The ERp29 D domain binds directly to the proline-rich P domains of CNX and CRT with micromolar affinity (Kd < 20 μM for CNX and ~13 μM for CRT), forming ternary chaperone-client complexes (kozlov2017mappingtheer pages 3-4, kozlov2017mappingtheer pages 4-5).

Kozlov et al. (2017) elucidated the structural basis of this interaction through crystallographic studies, showing that the tip of the CNX/CRT P domain inserts into a binding groove formed by helices α8 and α9 of the ERp29 D domain (kozlov2017mappingtheer pages 3-4, kozlov2017mappingtheer pages 4-5). A conserved aspartate residue (D348 in CNX, D248 in CRT) forms critical salt bridges with ERp29 R223, and mutation of D348K completely abrogates binding to ERp29, ERp57, and CypB, indicating that this residue serves as a universal binding site for multiple P-domain-recruited chaperones (kozlov2017mappingtheer pages 4-5, kozlov2017mappingtheer pages 5-6). This convergent evolution of binding sites allows CNX and CRT to recruit structurally diverse folding factors through a common P-domain adapter mechanism (kozlov2017mappingtheer pages 1-3, kozlov2017mappingtheer pages 5-6).

Substrate Specificity

ERp29 has been implicated in the folding and secretion of several specific protein substrates:

Thyroglobulin: ERp29 plays a crucial role in thyroglobulin (Tg) biogenesis and secretion, particularly evident in congenital hypothyroid disorders where mutant Tg accumulates in the ER (baryshev2004unfoldedproteinresponse pages 1-2). Baryshev et al. (2004) demonstrated that ERp29 associates with ER-retained mutant thyroglobulin in human congenital hypothyroid goiter and rat non-goitrous congenital hypothyroidism, suggesting its involvement in Tg quality control (baryshev2004unfoldedproteinresponse pages 1-2).

Collagen: ERp29 has been shown to facilitate collagen processing and secretion, working in concert with other ER chaperones to assist the complex folding and assembly of collagen molecules (kozlov2017mappingtheer pages 1-3).

Epithelial Sodium Channel (ENaC): ERp29 regulates ENaC biogenesis by directing the channel to the Golgi via coat protein complex II (COPII) during biogenesis, where it undergoes proteolytic cleavage that increases channel open probability (bikard2019thekdelreceptor pages 1-2). The KEEL motif and interaction with the KDEL-R are essential for this regulatory function (bikard2019thekdelreceptor pages 1-2).

Glycoproteins in the CNX/CRT Cycle: More broadly, ERp29 assists in the folding of glycoproteins that enter the calnexin/calreticulin quality control pathway, acting as an "attachment-enhancing" co-chaperone that stabilizes chaperone-client interactions (kozlov2017mappingtheer pages 1-3, sakono2022erendogenousprotein pages 2-4, mideksa2022acomprehensiveset pages 1-2).

Biochemical Pathways and Signaling Networks

Calnexin/Calreticulin Cycle

ERp29 is an integral component of the calnexin/calreticulin (CNX/CRT) cycle, a specialized ER quality control system for N-glycosylated proteins (kozlov2020calnexincycle– pages 1-3, suzuki2021foldingandquality pages 1-3). In this pathway, glucosidase I and II sequentially remove glucose residues from the Glc₃Man₉GlcNAc₂ glycan attached to nascent glycoproteins. The monoglucosylated form (Glc₁Man₉GlcNAc₂) specifically binds to CNX or CRT, creating a platform for recruiting ERp29, ERp57, and cyclophilin B (kozlov2020calnexincycle– pages 1-3). After glucosidase II removes the final glucose, properly folded proteins exit the cycle and proceed to the Golgi, while misfolded proteins are reglucosylated by UDP-glucose:glycoprotein glucosyltransferase (UGGT) for additional folding attempts (kozlov2020calnexincycle– pages 1-3, suzuki2021foldingandquality pages 1-3). ERp29's role in this cycle is to enhance chaperone function and client protein folding efficiency without directly catalyzing chemical modifications (kozlov2017mappingtheer pages 1-3, sakono2022erendogenousprotein pages 2-4).

ER Stress and Unfolded Protein Response

ERp29 is upregulated in response to ER stress and participates in the unfolded protein response (UPR) (huang2015erp29attenuatescigarette pages 1-2, baryshev2004unfoldedproteinresponse pages 1-2). Huang et al. (2015) demonstrated that ERp29 overexpression in retinal pigment epithelial cells increased levels of protective stress response proteins including GRP78, p58IPK, and Nrf2, while reducing pro-apoptotic markers phospho-eIF2α and CHOP (huang2015erp29attenuatescigarette pages 1-2). Conversely, ERp29 knockdown decreased p58IPK and Nrf2 levels, increased p-eIF2α and CHOP, and exacerbated cigarette smoke extract-induced cell death (huang2015erp29attenuatescigarette pages 1-2). These findings indicate that ERp29 attenuates ER stress through modulation of the ATF6-CHOP pathway and regulation of stress sensor proteins (huang2015erp29attenuatescigarette pages 1-2). Baryshev et al. (2004) observed upregulation of ERp29 alongside other ER chaperones (BiP, ERp72, calreticulin, PDI) in thyroid tissues with mutant thyroglobulin accumulation, consistent with activation of the UPR transcriptional arm (baryshev2004unfoldedproteinresponse pages 1-2).

Protein Secretory Pathway and COPII Trafficking

ERp29 regulates protein trafficking through the early secretory pathway via interactions with the COPII coat complex and the KDEL receptor (bikard2019thekdelreceptor pages 1-2). Bikard et al. (2019) showed that depletion of Sec24D, the cargo recognition component of COPII that interacts with ENaC, decreases ENaC functional expression, and that ERp29's KEEL motif is critical for proper ENaC trafficking and maturation (bikard2019thekdelreceptor pages 1-2). The dynamic cycling of ERp29 between the ER and Golgi via KDEL-R allows it to escort client proteins during forward trafficking while maintaining quality control checkpoints (bikard2019thekdelreceptor pages 1-2).

ER-Associated Degradation (ERAD)

ERp29 participates in ERAD-related quality control decisions, helping to distinguish between foldable and terminally misfolded proteins (suzuki2021foldingandquality pages 1-3, baryshev2004unfoldedproteinresponse pages 1-2). While ERp29 primarily functions to promote protein folding and secretion, it also contributes to the retention of irreparably misfolded proteins in the ER for subsequent degradation (suzuki2021foldingandquality pages 1-3, baryshev2004unfoldedproteinresponse pages 1-2).

Biological Processes and Recent Developments (2023-2024)

ER Stress and Reproductive Health

Recent work by Cicek et al. (2024) investigated ERp29 as a potential biomarker in idiopathic nonobstructive azoospermia, examining its role as an ER stress-regulated chaperone in male reproductive dysfunction (paskevicius2023calnexinmorethan pages 1-2). This study extends understanding of ERp29's involvement in tissue-specific stress responses.

Platelet Function and Hemostasis

Lay et al. (2023) demonstrated that ERp29 is secreted from platelets under conditions of ER stress and contributes to platelet ER homeostasis (paskevicius2023calnexinmorethan pages 1-2). Interestingly, He et al. (2024) used knockout mouse models to systematically evaluate PDI family members in venous thrombosis and found that ERp29-deficient mice showed no thrombotic phenotype in the inferior vena cava stenosis model, in contrast to ERp18-deficient mice which exhibited significantly reduced thrombosis (paskevicius2023calnexinmorethan pages 1-2). This suggests functional specialization among PDI family members in hemostatic processes.

Cancer Biology and Drug Resistance

Emerging evidence implicates ERp29 in cancer cell survival, drug resistance, and metastasis (yang2022rolesofprotein pages 1-2). Yang et al. (2022) reviewed the role of PDI family proteins in breast cancer, noting that ERp29 upregulates heat shock protein 27 (Hsp27), which confers resistance to doxorubicin-induced apoptosis in breast cancer cells (yang2022rolesofprotein pages 1-2). Multiple 2024 studies have linked ERp29 to epithelial-mesenchymal transition (EMT) regulation and cancer cell migration, suggesting that ERp29 may represent a therapeutic target for highly metastatic cancers (yang2022rolesofprotein pages 1-2).

Neurodevelopment

Sun et al. (2022) provided a comprehensive review of ERp29's role in neurodevelopment, highlighting its contribution to neural cell migration, neuronal morphogenesis, and synaptic function through regulation of ER proteostasis in the developing nervous system (paskevicius2023calnexinmorethan pages 1-2).

Structural Biology and Mechanistic Insights

Recent structural studies by Paskevicius et al. (2023) and Kozlov et al. (2020) have provided detailed mechanistic insights into ERp29 function within the CNX/CRT system (paskevicius2023calnexinmorethan pages 1-2, kozlov2020calnexincycle– pages 1-3). These studies emphasize ERp29's role as a plurivalent adapter that recruits diverse folding factors to glycoprotein clients through convergent evolution of binding sites on the P domains of lectin chaperones (kozlov2017mappingtheer pages 1-3, kozlov2020calnexincycle– pages 1-3).

Expert Opinions and Current Understanding

Current expert consensus views ERp29 as a specialized, non-catalytic PDI family member that couples client protein folding to lectin-chaperone recruitment and early secretory pathway trafficking (kozlov2017mappingtheer pages 1-3, adams2021theroleof pages 1-3, rahman2022functionsandmechanisms pages 1-2, kozlov2020calnexincycle– pages 1-3). Adams et al. (2021) note that ERp29, along with ERp57 and cyclophilin B, represents one of three known co-chaperones recruited to the CNX/CRT system to promote productive substrate folding (adams2021theroleof pages 1-3). The protein's unique D domain and loss of oxidoreductase activity during evolution suggest functional specialization toward chaperone and trafficking roles rather than disulfide bond catalysis (powell2021proteindisulphideisomerase pages 3-4, rahman2022functionsandmechanisms pages 1-2).

Kozlov and Gehring (2020) emphasize that the calnexin cycle components, including ERp29, reveal common features in how lectin chaperones recruit function-specific chaperones and how quality control mechanisms recognize misfolded proteins (kozlov2020calnexincycle– pages 1-3). The structural diversity of accessory factors binding to the same P-domain site (ERp29, ERp57, CypB) suggests convergent evolution of these chaperones to support glycoprotein folding through complementary mechanisms (kozlov2017mappingtheer pages 1-3, kozlov2017mappingtheer pages 5-6).

Conclusion

ERp29 (UniProt P30040) is a multifunctional ER-resident chaperone that plays critical roles in protein folding, quality control, and trafficking within the early secretory pathway. Distinguished from classical PDI enzymes by its lack of oxidoreductase activity, ERp29 functions primarily as a co-chaperone in the calnexin/calreticulin cycle and as a regulator of protein secretion through interactions with the KDEL receptor and COPII machinery. Its substrate specificity includes thyroglobulin, collagen, ENaC, and glycoproteins entering the CNX/CRT quality control pathway. ERp29 participates in multiple biochemical pathways including the UPR, ERAD, and ER-to-Golgi trafficking, with emerging roles in cancer biology, platelet function, and neurodevelopment. The protein's unique domain architecture and micromolar-affinity binding to CNX/CRT P domains position it as a key adapter molecule coordinating diverse folding factors in ER proteostasis. Recent structural and functional studies from 2020-2024 continue to elucidate ERp29's mechanistic contributions to cellular protein homeostasis and its potential as a therapeutic target in stress-related pathologies.

Key References:
- Kozlov et al. (2017) Structure 25:1415-1422 - Crystal structures of ERp29-P domain complexes (DOI: 10.1016/j.str.2017.07.010)
- Kozlov & Gehring (2020) FEBS J 287:4322-4340 - Calnexin cycle structural review (DOI: 10.1111/febs.15330)
- Bikard et al. (2019) J Biol Chem 294:18324-18336 - KDEL-R role in ENaC trafficking (DOI: 10.1074/jbc.ra119.008331)
- Huang et al. (2015) Invest Ophthalmol Vis Sci 56:6196-6207 - ERp29 in ER stress attenuation (DOI: 10.1167/iovs.15-16795)
- Paskevicius et al. (2023) Cells 12:403 - Calnexin review (DOI: 10.3390/cells12030403)
- Yang et al. (2022) Cancers 14:745 - PDI roles in breast cancer (DOI: 10.3390/cancers14030745)

References

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Artifacts

Edison artifact artifact-00

Citations

baryshev2004unfoldedproteinresponse pages 1-2
bikard2019thekdelreceptor pages 1-2
kozlov2017mappingtheer pages 1-3
paskevicius2023calnexinmorethan pages 1-2
yang2022rolesofprotein pages 1-2
adams2021theroleof pages 1-3
rahman2022functionsandmechanisms pages 1-2
sakono2022erendogenousprotein pages 2-4
powell2021proteindisulphideisomerase pages 3-4
kozlov2017mappingtheer pages 4-5
kozlov2017mappingtheer pages 5-6
kozlov2017mappingtheer pages 3-4
suzuki2021foldingandquality pages 1-3
mideksa2022acomprehensiveset pages 1-2
https://doi.org/10.1186/s13578-022-00868-6,
https://doi.org/10.4052/tigg.2119.1j,
https://doi.org/10.1002/cam4.3836,
https://doi.org/10.1167/iovs.15-16795,
https://doi.org/10.1074/jbc.ra119.008331,
https://doi.org/10.1016/j.str.2017.07.010,
https://doi.org/10.1007/978-3-030-67696-4_3,
https://doi.org/10.1111/febs.15330,
https://doi.org/10.1677/jme.0.0320903,
https://doi.org/10.1016/b978-0-12-409547-2.14947-9,
https://doi.org/10.1016/j.jbc.2022.102677,
https://doi.org/10.3390/cells12030403,
https://doi.org/10.3390/cancers14030745,

📚 Additional Documentation

Notes

(ERP29-notes.md)

ERP29 (ERp29, ERp28, ERp31, C12orf8) research notes

UniProt P30040. ER-lumenal, non-catalytic PDI-family escort/chaperone. Homodimer. KEEL ER-retention.

Core function

NOT a disulfide isomerase; lacks CXXC (CGHC) thioredoxin-box motif.
PMID:9738895
[file:human/ERP29/ERP29-uniprot.txt "Does not seem to be a disulfide isomerase. Plays an important role in the processing of secretory proteins within the endoplasmic reticulum (ER), possibly by participating in the folding of proteins in the ER."]
Acts as a non-catalytic escort/chaperone promoting folding/processing/secretion of secretory cargo.
Part of a large ER chaperone multiprotein complex with BiP/HSPA5, GRP94/HSP90B1, PDI, ERdj3/DNAJB11, cyclophilin B/PPIB, ERp72/PDIA4, UGGT1, SDF2L1, etc., binding nascent/unfolded Ig heavy chains.
PMID:12475965
Homodimer (GO:0042803 homodimerization activity).
ER lumen localization [file "SUBCELLULAR LOCATION: Endoplasmic reticulum lumen. Melanosome."]; also melanosome, cell surface (platelet), secreted.

Other roles (ParkinsonsUK-UCL curated, PMID:22064321 breast cancer model)

Cancer cell growth arrest via p38 MAPK activation, p58IPK upregulation; modulates gene expression and protein secretion.
PMID:22064321
These (pos reg MAPK, pos/neg reg gene expr, neg reg protein secretion) are context-specific (cancer cell overexpression) downstream effects -> KEEP_AS_NON_CORE.
protein unfolding (GO:0043335) NAS - ERp29 proposed to unfold cholera toxin/polyomavirus for membrane penetration; keep non-core.

Action plan

NOT|protein disulfide isomerase activity (GO:0003756) IKR negated - ACCEPT (correct, lacks CXXC).
ER / ER lumen localizations - ACCEPT.
smooth ER (ISS/IEA), melanosome, cell surface, extracellular, membrane - KEEP_AS_NON_CORE (secondary/peripheral).
protein folding (GO:0006457) NAS - KEEP_AS_NON_CORE (chaperone-assisted, not foldase).
protein secretion / intracellular protein transport / ER-Golgi transport - KEEP_AS_NON_CORE (processing of secretory proteins).
protein homodimerization activity (GO:0042803) - ACCEPT (real, homodimer).
protein-folding chaperone binding (GO:0051087) IEA/ISS - ACCEPT (binds chaperone complex; CORE MF candidate).
protein binding IPI (GLP1R, HT) - KEEP_AS_NON_CORE.
cancer/MAPK/gene-expr/secretion regulation - KEEP_AS_NON_CORE.
protein unfolding - KEEP_AS_NON_CORE.
ER stress apoptosis regulation IEA - KEEP_AS_NON_CORE.
Core MF: protein-folding chaperone binding (GO:0051087) + escort/chaperone in secretory protein processing.

Pn Notes

(ERP29-pn-notes.md)

ERP29 PN Consistency Notes

Generated: 2026-06-18
Project: PROTEOSTASIS
Scope: PN consistency rereview against local AIGR review and available deep-research artifacts
UniProt: P30040
AIGR review status: COMPLETE
Review batch: proteostasis-batch-2026-06-07b
Batch change status: added

Source Files Checked

AIGR review YAML: present - genes/human/ERP29/ERP29-ai-review.yaml
AIGR review HTML: present - genes/human/ERP29/ERP29-ai-review.html
Gene notes: present - genes/human/ERP29/ERP29-notes.md
GOA TSV: present - genes/human/ERP29/ERP29-goa.tsv
UniProt record: present - genes/human/ERP29/ERP29-uniprot.txt
PN dossier: projects/PROTEOSTASIS/reports/phase1_dossiers/ERP29.md
PN consistency section: projects/PROTEOSTASIS/reports/phase1_dossiers/_sections/ERP29.md
PN projection report: projects/PROTEOSTASIS/reports/pn_projection/pn_projected_gene_go_summary.tsv
PN mapping audit: projects/PROTEOSTASIS/reports/pn_mapping_audit/current_mapping_scrutiny.tsv

Deep Research Files

No *-deep-research*.md file found in this gene directory.

AIGR Review Snapshot

Description: ERP29 (endoplasmic reticulum resident protein 29; also called ERp28 and ERp31) is a soluble, ER-lumenal, homodimeric member of the protein disulfide isomerase (PDI) family that is catalytically redox-inactive - it has a thioredoxin-like fold but lacks the CXXC active-site motif and is not a disulfide isomerase. It functions as a non-catalytic escort/chaperone that assists the folding, processing and trafficking of secretory cargo in the ER, and is a component of a large ER chaperone multiprotein complex (containing BiP/HSPA5, GRP94/HSP90B1, PDI, the Hsp40 co-chaperone ERdj3/DNAJB11, cyclophilin B/PPIB, ERp72/PDIA4, UGGT1 and SDF2L1) that binds nascent, incompletely folded clients such as immunoglobulin heavy chains. It is retained in the ER lumen by a C-terminal KEEL retention signal and is broadly expressed, especially in secretory tissues; pools have also been detected at the cell surface, in melanosomes and secreted. Beyond its core chaperone role it has been implicated in handling of specific cargo (e.g. thyroglobulin, connexins) and in toxin/virus membrane penetration, and in cell-context-specific signaling (p38 MAPK, gene expression and secretion control in cancer models).
Existing/core annotation action counts: ACCEPT: 9; KEEP_AS_NON_CORE: 19; MARK_AS_OVER_ANNOTATED: 1

PN Consistency Summary

Consistency: Review, notes, and UniProt agree that ERP29 is a non-catalytic, redox-inactive PDI-family escort/chaperone — it has a thioredoxin-like fold but LACKS the CXXC (CGHC) active-site motif and is NOT a disulfide isomerase. The PN-node mapping CONTRADICTS this: the "Protein disulfide isomerases" group projects GO:0003756 positively onto ERP29, but ERP29's only GOA annotation to GO:0003756 is NOT|enables (IKR, PMID:9738895) and the review ACCEPTs that negation. So the PN group rationale ("catalytically active family members") is correct only for the catalytic PDIs — ERP29 is the family exception, mis-swept into the group projection.
PN story / NEW pressure: GO:0003756 (VERIFIED real via OLS) is a catalytic isomerase activity ERP29 demonstrably does not have. This is not a defensible NEW term for ERP29 — it directly opposes the negated experimental annotation and the no-CXXC biology. The review's true core MF is GO:0051087 protein-folding chaperone binding (ACCEPT), already captured. Conclude: OVER-REACHES (worse — actively contradicted), do NOT add.
Evidence alignment: PN node carries no reference titles. Review well-anchored: PMID:9738895 (lacks CXXC; founding characterization, VERIFIED) and PMID:12475965 (ER chaperone multiprotein complex, VERIFIED). No shared evidence supports a disulfide-isomerase-activity claim; the cited PMID:9738895 in fact establishes the opposite.
Verdict: OVER-REACHES / CONTRADICTED — reject projected GO:0003756 for ERP29; the gene is a non-catalytic PDI member whose function is already captured by GO:0051087. Recommended edits: [MAP] do not propagate GO:0003756 to ERP29 (it carries a curated NOT for this term); exclude non-catalytic PDI-family members from the group's isomerase projection or re-map ERP29 to GO:0051087 protein-folding chaperone binding.

Full Consistency Review

UniProt: P30040 · batch: proteostasis-batch-2026-06-07b · review status: COMPLETE (exhaustive; ~32 annotations, notes present, no provider deep-research file)
PN placement: ER proteostasis|Folding enzyme|Protein disulfide isomerases ; PN-node mapping: group (Protein disulfide isomerases)→GO:0003756 protein disulfide isomerase activity (mapped/ok_for_propagation, goa_status=new_to_goa); class (Folding enzyme)→no_mapping; branch→no_mapping.
Consistency: Review, notes, and UniProt agree that ERP29 is a non-catalytic, redox-inactive PDI-family escort/chaperone — it has a thioredoxin-like fold but LACKS the CXXC (CGHC) active-site motif and is NOT a disulfide isomerase. The PN-node mapping CONTRADICTS this: the "Protein disulfide isomerases" group projects GO:0003756 positively onto ERP29, but ERP29's only GOA annotation to GO:0003756 is NOT|enables (IKR, PMID:9738895) and the review ACCEPTs that negation. So the PN group rationale ("catalytically active family members") is correct only for the catalytic PDIs — ERP29 is the family exception, mis-swept into the group projection.
PN story / NEW pressure: GO:0003756 (VERIFIED real via OLS) is a catalytic isomerase activity ERP29 demonstrably does not have. This is not a defensible NEW term for ERP29 — it directly opposes the negated experimental annotation and the no-CXXC biology. The review's true core MF is GO:0051087 protein-folding chaperone binding (ACCEPT), already captured. Conclude: OVER-REACHES (worse — actively contradicted), do NOT add.
Mapping strategy: This gene SHOULD change the group projection. The catalytic-PDI mapping (GO:0003756) is the right target for active members (PDIA1, etc.) but must NOT propagate to the non-catalytic ERP29; the group node needs a per-member exclusion or ERP29 should map to a chaperone-binding/escort term (GO:0051087) instead.
Evidence alignment: PN node carries no reference titles. Review well-anchored: PMID:9738895 (lacks CXXC; founding characterization, VERIFIED) and PMID:12475965 (ER chaperone multiprotein complex, VERIFIED). No shared evidence supports a disulfide-isomerase-activity claim; the cited PMID:9738895 in fact establishes the opposite.
Verdict: OVER-REACHES / CONTRADICTED — reject projected GO:0003756 for ERP29; the gene is a non-catalytic PDI member whose function is already captured by GO:0051087. Recommended edits: [MAP] do not propagate GO:0003756 to ERP29 (it carries a curated NOT for this term); exclude non-catalytic PDI-family members from the group's isomerase projection or re-map ERP29 to GO:0051087 protein-folding chaperone binding.

PN Dossier Context

review_batch: proteostasis-batch-2026-06-07b
review_yaml: genes/human/ERP29/ERP29-ai-review.yaml
PN workbook rows: 1

PN row 1: ER proteostasis | Folding enzyme | Protein disulfide isomerases

UniProt: P30040
In branches: ER
PN-node mapping records (path + ancestors):
- [group] ER proteostasis|Folding enzyme|Protein disulfide isomerases
  status=mapped scope=ok_for_propagation_to_go GO=[GO:0003756 protein disulfide isomerase activity]
  rationale: This PN group captures the canonical ER protein-disulfide-isomerase folding enzymes. GO protein disulfide isomerase activity is the cleanest propagation target for the catalytically active family members.
- [class] ER proteostasis|Folding enzyme
  status=no_mapping scope= GO=[]
  rationale: Reviewed as a broad PN category rather than a single GO class. The member genes span multiple activities, complexes, or contexts, so direct propagation from this node would overstate the shared biology.
- [branch] ER proteostasis
  status=no_mapping scope= GO=[]
  rationale: Reviewed as a top-level PN branch. This is a systems/taxonomy umbrella, not a direct GO assertion; narrower child curations carry any propagating GO mappings.

Projected GO annotations (1)

GO:0003756 protein disulfide isomerase activity | scope=ok_for_propagation_to_go | goa_status=new_to_goa | from=ER proteostasis|Folding enzyme|Protein disulfide isomerases

Note

This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.

📄 View Raw YAML

id: P30040
gene_symbol: ERP29
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
alternative_products:
- name: '1'
  id: P30040-1
- name: '2'
  id: P30040-2
  sequence_note: VSP_045680, VSP_045681
description: ERP29 (endoplasmic reticulum resident protein 29; also called ERp28 and ERp31) is a soluble, ER-lumenal, homodimeric member of the protein disulfide isomerase (PDI) family that is catalytically redox-inactive - it has a thioredoxin-like fold but lacks the CXXC active-site motif and is not a disulfide isomerase. It functions as a non-catalytic escort/chaperone that assists the folding, processing and trafficking of secretory cargo in the ER, and is a component of a large ER chaperone multiprotein complex (containing BiP/HSPA5, GRP94/HSP90B1, PDI, the Hsp40 co-chaperone ERdj3/DNAJB11, cyclophilin B/PPIB, ERp72/PDIA4, UGGT1 and SDF2L1) that binds nascent, incompletely folded clients such as immunoglobulin heavy chains. It is retained in the ER lumen by a C-terminal KEEL retention signal and is broadly expressed, especially in secretory tissues; pools have also been detected at the cell surface, in melanosomes and secreted. Beyond its core chaperone role it has been implicated in handling of specific cargo (e.g. thyroglobulin, connexins) and in toxin/virus membrane penetration, and in cell-context-specific signaling (p38 MAPK, gene expression and secretion control in cancer models).
existing_annotations:
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: ERP29 is an ER-resident lumenal protein; the ER is its primary site of action.
    action: ACCEPT
    reason: ER localization is well supported (retention signal, immunofluorescence, fractionation) and is the core compartment for ERP29's chaperone function.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: located_in
  review:
    summary: Electronic ER localization, consistent with the IBA/IDA evidence.
    action: ACCEPT
    reason: Correct compartment for this ER-resident chaperone.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0005788
    label: endoplasmic reticulum lumen
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: ERP29 is a soluble ER-lumenal protein with a KEEL retention signal; the precise compartment.
    action: ACCEPT
    reason: ER lumen is the documented, precise localization for this soluble chaperone.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0009306
    label: protein secretion
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: ERP29 participates in the processing and secretion of secretory proteins; a plausible downstream process of its chaperone role.
    action: KEEP_AS_NON_CORE
    reason: ERP29 facilitates secretory-protein processing/trafficking, so a protein-secretion process annotation is reasonable but is a downstream consequence of its chaperone function rather than a direct molecular activity.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: Plays an important role in the processing of secretory proteins within the endoplasmic reticulum
- term:
    id: GO:0042470
    label: melanosome
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: ERP29 was identified by mass spectrometry in melanosome fractions; a secondary localization.
    action: KEEP_AS_NON_CORE
    reason: A proteomics-detected secondary localization, peripheral to the core ER-lumenal chaperone function.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: Identified by mass spectrometry in melanosome fractions
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:23864651
  qualifier: enables
  review:
    summary: Interaction with the GLP-1 receptor (GLP1R/P43220) identified in a screen for GLP1R-interacting proteins. The bare protein binding term is uninformative.
    action: KEEP_AS_NON_CORE
    reason: A specific interaction (GLP1R) consistent with ERP29 handling secretory/membrane clients, but the generic protein binding term is uninformative and not core.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'P30040; P43220: GLP1R; NbExp=2; IntAct=EBI-946830, EBI-7466542;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: Reference binary interactome capturing many ERP29 interactions (e.g. SGTA, SGTB, TMBIM6, UBQLN1/2). Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: High-throughput binary interactions; the generic protein binding term is uninformative and not part of the core function.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'P30040; O43765: SGTA; NbExp=3; IntAct=EBI-946830, EBI-347996;'
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: Extracellular/secreted pool inferred from the rat ortholog; peripheral to the ER chaperone role.
    action: KEEP_AS_NON_CORE
    reason: A secreted pool is reported (and ERP29 is detected at the cell surface), but this is secondary to its core ER-lumenal localization.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: Melanosome.
- term:
    id: GO:0005790
    label: smooth endoplasmic reticulum
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: Smooth-ER localization inferred from the rat ortholog; a sub-compartment refinement of the ER localization.
    action: KEEP_AS_NON_CORE
    reason: A plausible ER sub-compartment annotation transferred by similarity; subsumed by the core ER/ER-lumen localization.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0006888
    label: endoplasmic reticulum to Golgi vesicle-mediated transport
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: ER-to-Golgi transport role inferred from the rat ortholog; consistent with ERP29's role in secretory-cargo trafficking. The falcon deep research corroborates a role in the early secretory pathway, with ERP29 cycling between ER and Golgi via the KDEL receptor (its weaker KEEL retention variant) to escort clients such as ENaC.
    action: KEEP_AS_NON_CORE
    reason: A plausible downstream trafficking process inferred by similarity; non-core relative to the chaperone molecular function. The falcon deep research provides additional (unverified) support for dynamic ER-to-Golgi cycling via the KDEL receptor and a role in client forward trafficking, reinforcing the biological plausibility of this process annotation.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: Plays an important role in the processing of secretory proteins within the endoplasmic reticulum
    - reference_id: file:human/ERP29/ERP29-deep-research-falcon.md
      supporting_text: dynamic cycling between the ER and Golgi apparatus via interactions with the KDEL receptor
- term:
    id: GO:0009725
    label: response to hormone
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: A broad 'response to hormone' process inferred from the rat ortholog; vague and not characteristic of ERP29's molecular function.
    action: MARK_AS_OVER_ANNOTATED
    reason: An unspecific, by-similarity process annotation with no direct human evidence and no clear connection to ERP29's chaperone function; over-annotated.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-goa.tsv
      supporting_text: GO:0009725
- term:
    id: GO:0009986
    label: cell surface
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: Cell-surface localization inferred from the mouse ortholog; corroborated by direct evidence in platelets, but secondary to the ER role.
    action: KEEP_AS_NON_CORE
    reason: A genuine but minor surface pool (also IDA in platelets); peripheral to ERP29's core ER-lumenal chaperone function.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: Melanosome.
- term:
    id: GO:0042803
    label: protein homodimerization activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: enables
  review:
    summary: ERP29 functions as a homodimer; homodimerization is a genuine structural property documented by UniProt and crystal structures.
    action: ACCEPT
    reason: ERP29 is a well-documented homodimer; homodimerization activity is correct, though it is structural rather than the principal client-facing function.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'SUBUNIT: Homodimer.'
- term:
    id: GO:0051087
    label: protein-folding chaperone binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: enables
  review:
    summary: ERP29 binds molecular chaperones as part of a large ER chaperone complex (BiP, GRP94, PDI, ERdj3, cyclophilin B, ERp72, etc.) and, per the falcon deep research, is recruited to the calnexin/calreticulin (CNX/CRT) lectin-chaperone cycle, with its C-terminal D domain serving as the binding interface for the CNX/CRT P domains; chaperone binding is central to its escort function.
    action: ACCEPT
    reason: ERP29's participation in the ER chaperone multiprotein complex is experimentally documented; protein-folding chaperone binding is an informative, core molecular function. The falcon deep research adds a specific mechanistic basis - ERP29 is recruited as a function-specific co-chaperone within the calnexin/calreticulin cycle via direct binding of its D domain to the CNX/CRT P domains - consistent with this chaperone-binding annotation (these CNX/CRT-cycle citations were not independently verified against cached publications).
    supported_by:
    - reference_id: PMID:12475965
      supporting_text: large endoplasmic reticulum (ER)-localized multiprotein complex that is comprised of the molecular chaperones BiP
    - reference_id: file:human/ERP29/ERP29-deep-research-falcon.md
      supporting_text: C-terminal D domain serves as the principal binding interface for lectin chaperones in the calnexin/calreticulin system
- term:
    id: GO:1902235
    label: regulation of endoplasmic reticulum stress-induced intrinsic apoptotic signaling pathway
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: A role in regulating ER-stress-induced apoptosis inferred from the mouse ortholog; consistent with ERP29's ER-stress-related functions but indirect. The falcon deep research reports human-cell evidence (RPE cells) that ERP29 overexpression raises protective stress proteins (GRP78, p58IPK, Nrf2) and lowers pro-apoptotic CHOP, supporting a protective modulation of ER-stress-induced apoptotic signaling.
    action: KEEP_AS_NON_CORE
    reason: A plausible context-specific process inferred by similarity; non-core relative to the chaperone molecular function. The falcon deep research adds (unverified) supportive evidence that ERP29 attenuates ER stress and shifts the balance away from CHOP-driven apoptosis, consistent with this regulatory annotation though still peripheral to its core chaperone-binding function.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: Plays an important role in the processing of secretory proteins within the endoplasmic reticulum
    - reference_id: file:human/ERP29/ERP29-deep-research-falcon.md
      supporting_text: increased levels of protective stress response proteins including GRP78, p58IPK, and Nrf2, while reducing pro-apoptotic markers phospho-eIF2α and CHOP
- term:
    id: GO:0043410
    label: positive regulation of MAPK cascade
  evidence_type: IDA
  original_reference_id: PMID:22064321
  qualifier: involved_in
  review:
    summary: In breast cancer cells, ERP29 overexpression activates p38 MAPK and induces growth arrest; a cell-context-specific signaling effect.
    action: KEEP_AS_NON_CORE
    reason: Documented in a cancer-overexpression model; a specialized downstream signaling effect rather than ERP29's core ER chaperone function.
    supported_by:
    - reference_id: PMID:22064321
      supporting_text: ERp29-induced cancer cell growth arrest is modulated by the interplay between the concomitant phosphorylation of p38
- term:
    id: GO:0005790
    label: smooth endoplasmic reticulum
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: located_in
  review:
    summary: ISS smooth-ER localization (rat ortholog); a sub-compartment refinement.
    action: KEEP_AS_NON_CORE
    reason: Redundant with the IEA smooth-ER annotation; subsumed by the core ER/ER-lumen localization.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0051087
    label: protein-folding chaperone binding
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: enables
  review:
    summary: ISS protein-folding chaperone binding (rat ortholog), consistent with ERP29's role in the ER chaperone complex.
    action: ACCEPT
    reason: Corroborates the experimentally supported chaperone-binding function (ER chaperone complex membership); an informative core molecular function.
    supported_by:
    - reference_id: PMID:12475965
      supporting_text: large endoplasmic reticulum (ER)-localized multiprotein complex that is comprised of the molecular chaperones BiP
- term:
    id: GO:0003756
    label: protein disulfide isomerase activity
  evidence_type: IKR
  original_reference_id: PMID:9738895
  qualifier: enables
  negated: true
  review:
    summary: This is a NOT (negated) annotation - ERP29 does NOT have protein disulfide isomerase activity, because it lacks the CXXC thioredoxin-box motif. The negation is correct.
    action: ACCEPT
    reason: Directly supported - ERP29 lacks the CXXC (CGHC) active-site motif and is not a disulfide isomerase; the NOT annotation correctly blocks transfer of isomerase activity. The falcon deep research independently affirms the redox-inactive, non-catalytic nature of ERP29 (lacks the CXXC catalytic motif; functions as a chaperone, not a catalyst).
    supported_by:
    - reference_id: PMID:9738895
      supporting_text: member of the protein disulfide isomerase family but lacks a CXXC thioredoxin-box motif
    - reference_id: file:human/ERP29/ERP29-deep-research-falcon.md
      supporting_text: lacks the characteristic CXXC catalytic motif
    - reference_id: file:human/ERP29/ERP29-deep-research-falcon.md
      supporting_text: establishing its primary role as a chaperone rather than a catalyst
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: IDA
  original_reference_id: PMID:9738895
  qualifier: located_in
  review:
    summary: Direct evidence (fractionation and immunofluorescence) for ER localization.
    action: ACCEPT
    reason: IDA-supported ER localization from the founding characterization.
    supported_by:
    - reference_id: PMID:9738895
      supporting_text: localizes to the endoplasmic reticulum (ER) as seen by subcellular fractionation and immunofluorescence studies
- term:
    id: GO:0005788
    label: endoplasmic reticulum lumen
  evidence_type: NAS
  original_reference_id: PMID:22064321
  qualifier: located_in
  review:
    summary: ER-lumen localization asserted in the literature; correct and core.
    action: ACCEPT
    reason: ERP29 is a soluble ER-lumenal protein; consistent with its retention signal and direct localization data.
    supported_by:
    - reference_id: PMID:22064321
      supporting_text: ERp29) is an ER luminal protein
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: NAS
  original_reference_id: PMID:9738895
  qualifier: involved_in
  review:
    summary: ERP29 may participate in folding of secretory proteins as a non-catalytic chaperone; protein folding is a plausible downstream process.
    action: KEEP_AS_NON_CORE
    reason: ERP29 assists folding indirectly as an escort/chaperone (it is not a foldase); protein folding is a non-core process annotation.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: possibly by participating in the folding of proteins in the ER
- term:
    id: GO:0006886
    label: intracellular protein transport
  evidence_type: NAS
  original_reference_id: PMID:9738895
  qualifier: involved_in
  review:
    summary: ERP29 participates in the trafficking/processing of secretory proteins; intracellular protein transport is a plausible downstream process.
    action: KEEP_AS_NON_CORE
    reason: A reasonable downstream process consequence of ERP29's escort/chaperone role; non-core relative to its molecular function.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: Plays an important role in the processing of secretory proteins within the endoplasmic reticulum
- term:
    id: GO:0010628
    label: positive regulation of gene expression
  evidence_type: IDA
  original_reference_id: PMID:22064321
  qualifier: involved_in
  review:
    summary: In a breast-cancer overexpression model, ERP29 modulates gene expression (e.g. upregulation of p58IPK); a context-specific downstream effect.
    action: KEEP_AS_NON_CORE
    reason: A specialized, cell-context-specific transcriptional effect from an overexpression study; not ERP29's core ER chaperone function.
    supported_by:
    - reference_id: PMID:22064321
      supporting_text: upregulation of the inhibitor of the interferon-induced, double-stranded RNA-activated protein kinase, p58(IPK)
- term:
    id: GO:0010629
    label: negative regulation of gene expression
  evidence_type: IDA
  original_reference_id: PMID:22064321
  qualifier: involved_in
  review:
    summary: ERP29 also negatively regulates expression of certain genes in the cancer-cell model; a context-specific downstream effect.
    action: KEEP_AS_NON_CORE
    reason: A specialized transcriptional effect in an overexpression model; non-core relative to the chaperone function.
    supported_by:
    - reference_id: PMID:22064321
      supporting_text: ERp29-induced cancer cell growth arrest
- term:
    id: GO:0043335
    label: protein unfolding
  evidence_type: NAS
  original_reference_id: PMID:22064321
  qualifier: involved_in
  review:
    summary: ERP29 has been proposed to have a protein-unfolding activity (e.g. in toxin/virus membrane penetration); asserted in the literature but mechanistically limited.
    action: KEEP_AS_NON_CORE
    reason: A proposed specialized activity (substrate unfolding/local conformational change) rather than ERP29's principal chaperone-binding function; retained as non-core.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: a role in protein unfolding and secretion
- term:
    id: GO:0050709
    label: negative regulation of protein secretion
  evidence_type: IDA
  original_reference_id: PMID:22064321
  qualifier: involved_in
  review:
    summary: ERP29 overexpression can negatively regulate secretion of specific proteins in the cancer model; a context-specific effect.
    action: KEEP_AS_NON_CORE
    reason: A specialized, context-dependent secretion-regulation effect; non-core relative to the chaperone function.
    supported_by:
    - reference_id: PMID:22064321
      supporting_text: ERp29) is an ER luminal protein that has a role in protein unfolding and secretion
- term:
    id: GO:0016020
    label: membrane
  evidence_type: HDA
  original_reference_id: PMID:19946888
  qualifier: located_in
  review:
    summary: High-throughput membrane-proteome detection; generic and uninformative for this soluble ER-lumenal protein (likely reflects ER-membrane-associated complexes or surface pool).
    action: KEEP_AS_NON_CORE
    reason: A generic proteomic localization; uninformative relative to the precise ER-lumen localization.
    supported_by:
    - reference_id: file:human/ERP29/ERP29-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0009986
    label: cell surface
  evidence_type: IDA
  original_reference_id: PMID:19995400
  qualifier: located_in
  review:
    summary: Direct evidence that ERP29 (a thiol-isomerase-family protein) is released by platelets and recruited to the cell surface upon activation; a genuine but specialized surface pool.
    action: KEEP_AS_NON_CORE
    reason: A real activation-dependent surface pool in platelets, but peripheral to ERP29's core ER-lumenal chaperone function.
    supported_by:
    - reference_id: PMID:19995400
      supporting_text: Platelets release novel thiol isomerase enzymes which are recruited to the cell surface following activation
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB Subcellular Location vocabulary mapping
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:9738895
  title: ERp28, a human endoplasmic-reticulum-lumenal protein, is a member of the protein disulfide isomerase family but lacks a CXXC thioredoxin-box motif.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: "Cached publications/PMID_9738895.md title matches YAML; establishes ERP29 as an ER-lumenal PDI-family member lacking the CXXC motif (non-catalytic), central to its core chaperone/escort identity. GOA anchors this PMID to GO:0005783 (ER, IDA) and GO:0003756 (IKR, i.e. NOT a disulfide isomerase)."
  findings:
  - statement: ERp28/ERp29 is an ER-lumenal protein with a KEEL retention signal that is a PDI-family member but lacks the CXXC (CGHC) thioredoxin-box motif, hence is not a disulfide isomerase.
    reference_section_type: ABSTRACT
- id: PMID:12475965
  title: A subset of chaperones and folding enzymes form multiprotein complexes in endoplasmic reticulum to bind nascent proteins.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: "Cached publications/PMID_12475965.md title matches YAML; supports the core MF (protein-folding chaperone binding) by showing ERP29 participates in ER multiprotein chaperone/folding-enzyme complexes binding nascent proteins."
  findings:
  - statement: ERp29 is part of a large ER chaperone multiprotein complex (BiP, GRP94, PDI, ERdj3, cyclophilin B, ERp72, GRP170, UGGT, SDF2-L1) that binds unassembled, incompletely folded immunoglobulin heavy chains.
    reference_section_type: RESULTS
- id: PMID:19946888
  title: Defining the membrane proteome of NK cells.
  findings: []
- id: PMID:19995400
  title: Platelets release novel thiol isomerase enzymes which are recruited to the cell surface following activation.
  findings:
  - statement: ERP29 is among thiol-isomerase-family proteins released by platelets and recruited to the platelet surface following activation.
    reference_section_type: RESULTS
- id: PMID:22064321
  title: ERp29 induces breast cancer cell growth arrest and survival through modulation of activation of p38 and upregulation of ER stress protein p58IPK.
  findings:
  - statement: In breast cancer cells, ERp29 (an ER luminal protein with a role in protein unfolding and secretion) overexpression induces growth arrest via p38 MAPK activation and upregulation of p58IPK, modulating gene expression and protein secretion.
    reference_section_type: ABSTRACT
- id: PMID:23864651
  title: The identification of novel proteins that interact with the GLP-1 receptor and restrain its activity.
  findings: []
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
- id: file:human/ERP29/ERP29-uniprot.txt
  title: UniProt entry P30040 (ERP29_HUMAN), Endoplasmic reticulum resident protein 29
  findings:
  - statement: Non-catalytic (no CXXC) PDI-family ER-lumenal homodimeric chaperone that assists processing/folding of secretory proteins; part of a large ER chaperone complex; KEEL ER-retention signal; also detected in melanosomes and at the cell surface.
    reference_section_type: OTHER
- id: file:human/ERP29/ERP29-deep-research-falcon.md
  title: Falcon deep research report for ERP29
  reference_review:
    relevance: MEDIUM
    correctness: UNVERIFIED
    review_notes: "LLM-synthesized (Edison/Falcon) deep-research report; its underlying primary citations (Kozlov 2017, Bikard 2019, Baryshev 2004, Huang 2015, etc.) are NOT in the publications cache and were not independently verified here, hence UNVERIFIED. The report is consistent with the established ERP29-specific picture: it correctly frames ERP29 as a non-catalytic, CXXC-lacking PDI-family chaperone (NOT a disulfide isomerase) and as a calnexin/calreticulin (CNX/CRT) co-chaperone whose D domain binds the CNX/CRT P domains. CAUTION: the report carries PDI-family background on oxidoreductase/disulfide-isomerase catalysis by family analogy; do NOT attribute any disulfide isomerase / oxidoreductase catalytic activity to the redox-inactive ERP29 on that basis. Used here only to strengthen non-catalytic chaperone-binding, ER-stress, and early-secretory-pathway trafficking annotations with verbatim quotes."
  findings:
  - statement: ERP29 lacks the characteristic CXXC catalytic motif of classical PDIs and acts as a chaperone rather than a catalyst; it is recruited to the calnexin/calreticulin cycle, its C-terminal D domain being the principal interface that binds the CNX/CRT P domains, and it cycles between ER and Golgi via the KDEL receptor (KEEL motif) to assist early-secretory-pathway folding/trafficking of clients such as thyroglobulin and ENaC.
    reference_section_type: OTHER
core_functions:
- description: Non-catalytic, ER-lumenal escort/chaperone of the PDI family (lacking a CXXC active site) that assists the folding, processing and trafficking of secretory cargo by binding molecular chaperones within a large ER chaperone multiprotein complex.
  molecular_function:
    id: GO:0051087
    label: protein-folding chaperone binding
  locations:
  - id: GO:0005788
    label: endoplasmic reticulum lumen
  supported_by:
  - reference_id: PMID:12475965
    supporting_text: large endoplasmic reticulum (ER)-localized multiprotein complex that is comprised of the molecular chaperones BiP
  - reference_id: file:human/ERP29/ERP29-uniprot.txt
    supporting_text: Plays an important role in the processing of secretory proteins within the endoplasmic reticulum
proposed_new_terms: []
suggested_questions:
- question: What is the precise molecular contribution of ERP29 within the ER chaperone complex - does it have client specificity (e.g. thyroglobulin, connexins) distinct from its homodimerization and chaperone-binding roles?
- question: Are the cancer-associated signaling phenotypes (p38 MAPK, gene-expression and secretion control) a direct consequence of ERP29's ER chaperone function or secondary to altered ER proteostasis?
suggested_experiments:
- description: Reconstitute ERP29 within the ER chaperone complex and test, with defined unfolded clients, whether ERP29 modulates client binding, folding kinetics or release relative to ERP29-depleted complexes.
- description: ERP29 knockout/knockdown in secretory cell types followed by secretome and client-folding analysis (e.g. thyroglobulin, connexin trafficking) to define its non-redundant chaperone clients.

ERP29

Gene Description

Existing Annotations Review

Core Functions

Non-catalytic, ER-lumenal escort/chaperone of the PDI family (lacking a CXXC active site) that assists the folding, processing and trafficking of secretory cargo by binding molecular chaperones within a large ER chaperone multiprotein complex.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Comprehensive Research Report: ERP29 Gene (UniProt P30040) - Functional Annotation

Gene Identity and Overview

Structural Features and Domain Organization

Subcellular Localization

Primary Molecular Functions and Substrate Specificity

Chaperone Function

Recruitment to the Calnexin/Calreticulin Cycle

Substrate Specificity

Biochemical Pathways and Signaling Networks

Calnexin/Calreticulin Cycle

ER Stress and Unfolded Protein Response

Protein Secretory Pathway and COPII Trafficking

ER-Associated Degradation (ERAD)

Biological Processes and Recent Developments (2023-2024)

ER Stress and Reproductive Health

Platelet Function and Hemostasis

Cancer Biology and Drug Resistance

Neurodevelopment

Structural Biology and Mechanistic Insights

Expert Opinions and Current Understanding

Conclusion

Artifacts

Citations

📚 Additional Documentation

Notes

ERP29 (ERp29, ERp28, ERp31, C12orf8) research notes

Core function

Other roles (ParkinsonsUK-UCL curated, PMID:22064321 breast cancer model)

Action plan

Pn Notes

ERP29 PN Consistency Notes

Source Files Checked

Deep Research Files

AIGR Review Snapshot

PN Consistency Summary

Full Consistency Review

PN Dossier Context

PN row 1: ER proteostasis | Folding enzyme | Protein disulfide isomerases

Projected GO annotations (1)

Note

📄 View Raw YAML