Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005929 cilium	IBA GO_REF:0000033	MARK AS OVER ANNOTATED	Summary: Phylogenetic (IBA) localization to cilium. The primary functional study explicitly found that LZTFL1 is cytoplasmic and is NOT enriched in cilia or basal bodies; it acts on the BBSome in the cytoplasm to regulate ciliary entry. LZTFL1 acts upon ciliary trafficking but is not itself a ciliary-resident protein, so "is_active_in cilium" overstates its localization. Reason: PMID:22072986 directly shows LZTFL1 is cytoplasmic without ciliary/centriolar enrichment, and that the LZTFL1-BBSome interaction occurs in the cytoplasm. The cytosol/cytoplasm annotations better capture where it acts.
GO:0030317 flagellated sperm motility	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: Phylogenetic inference of a role in flagellated sperm motility. LZTFL1 is highly expressed in testis, the mouse ortholog localizes to the sperm flagellum/manchette region, and BBS proteins are required for sperm flagella; a contribution to sperm function is plausible but is a peripheral, tissue-specific role rather than the core molecular activity of the protein. Falcon deep research summarizes mouse knockout data (Huang 2021) in which Lztfl1-null males have reduced fertility with low sperm motility and abnormal sperm (astheno-teratozoospermia), consistent with this process annotation (in the rodent ortholog). Reason: Consistent with testis expression and the BBS/ciliopathy context, and corroborated by the mouse-ortholog knockout sperm-motility phenotype summarized in the falcon deep research, but this is a downstream/tissue-specific process, not the core BBSome-trafficking-regulator function. Retain as non-core. Supporting Evidence: file:human/LZTFL1/LZTFL1-deep-research-falcon.md Lztfl1-knockout male mice exhibit significantly reduced fertility associated with low sperm motility and high levels of abnormal sperm, a condition termed astheno-teratozoospermia
GO:0005737 cytoplasm	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetic localization to cytoplasm, consistent with direct experimental evidence that LZTFL1 is a cytoplasmic protein that binds and regulates the BBSome in the cytoplasm. Reason: Strongly supported by PMID:22072986 (cytoplasmic localization) and UniProt subcellular location (Cytoplasm). Supporting Evidence: PMID:22072986 LZTFL1 was detected throughout the cytoplasm
GO:1903565 negative regulation of protein localization to cilium	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetic inference of the core function: LZTFL1 negatively regulates localization of the BBSome (and its cargo) to the cilium. Captures the central biological role and is corroborated by direct experimental (IMP) evidence in human cells. Falcon deep research adds a mechanistic link: LZTFL1 physically interacts with IFT27 (an IFT-B subunit), connecting it to the IFT-B/BBSome axis that controls BBSome ciliary entry/export (Huang 2021). Reason: Core function. Supported by IBA and by IMP (PMID:22072986): LZTFL1 depletion increases, and overexpression decreases, BBSome ciliary localization. The LZTFL1-IFT27 interaction summarized in the falcon deep research provides a candidate molecular coupling to the IFT machinery (note: GPCR-export and Hedgehog effects are largely whole-pathway behaviors of the IFT27/BBSome axis rather than demonstrated LZTFL1-protein activities, so they are not annotated to LZTFL1 here). Supporting Evidence: PMID:22072986 LZTFL1 is a specific regulator of BBSome ciliary trafficking but not general IFT file:human/LZTFL1/LZTFL1-deep-research-falcon.md LZTFL1 physically interacts with IFT27, a component of the IFT-B complex, as demonstrated by yeast two-hybrid screening, co-immunoprecipitation, colocalization studies, and luciferase complementation assays
GO:0005737 cytoplasm	IEA GO_REF:0000120	ACCEPT	Summary: Electronic (IEA) cytoplasm localization, consistent with the IBA and experimental cytosol annotations. Reason: Consistent with experimentally established cytoplasmic localization (PMID:22072986).
GO:0005515 protein binding	IPI PMID:22072986 A novel protein LZTFL1 regulates ciliary trafficking of the ...	MARK AS OVER ANNOTATED	Summary: Generic protein binding (IPI) from interaction with BBS9 (Q3SYG4). The underlying interaction is real and biologically central, but the bare "protein binding" term is uninformative; the BBSome-binding activity is better captured by protein-containing complex binding. Reason: Per curation guidelines, avoid uninformative "protein binding". The BBS9/BBSome interaction is better represented by GO:0044877 (protein-containing complex binding), already annotated.
GO:0005515 protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	MARK AS OVER ANNOTATED	Summary: Generic protein binding from a large-scale interactome screen (partners include SDCBP). Uninformative term. Reason: Uninformative "protein binding"; high-throughput interactome data without specific functional meaning.
GO:0005515 protein binding	IPI PMID:27173435 An organelle-specific protein landscape identifies novel dis...	MARK AS OVER ANNOTATED	Summary: Generic protein binding (interaction with BBS9, Q3SYG4) from an organelle proteome map. Uninformative term. Reason: Uninformative "protein binding"; better captured by protein-containing complex binding for the BBSome.
GO:0005515 protein binding	IPI PMID:28514442 Architecture of the human interactome defines protein commun...	MARK AS OVER ANNOTATED	Summary: Generic protein binding (BBS9, Q3SYG4) from a large-scale interactome study. Uninformative term. Reason: Uninformative "protein binding"; high-throughput interactome data.
GO:0005515 protein binding	IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari...	MARK AS OVER ANNOTATED	Summary: Generic protein binding (NTAQ1, Q96HA8) from a population variant interactome study. Uninformative term. Reason: Uninformative "protein binding"; high-throughput interactome data.
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	MARK AS OVER ANNOTATED	Summary: Generic protein binding from the HuRI reference binary interactome (partners include proteasome subunits PSMA1/PSMB1, MOB1A, PELI2, PICK1, TRIM68, EHHADH). Uninformative term. Reason: Uninformative "protein binding"; high-throughput binary interactome data.
GO:0005515 protein binding	IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling...	MARK AS OVER ANNOTATED	Summary: Generic protein binding (BBS9, Q3SYG4) from the BioPlex interactome. Uninformative term. Reason: Uninformative "protein binding"; high-throughput interactome data.
GO:0042802 identical protein binding	IPI PMID:22072986 A novel protein LZTFL1 regulates ciliary trafficking of the ...	ACCEPT	Summary: Self/identical protein binding (Q9NQ48 with Q9NQ48). Strongly supported by directed experiments showing LZTFL1 forms homo-oligomers (co-purification of endogenous LZTFL1, co-IP, and in vitro crosslinking). Reason: PMID:22072986 demonstrates homo-oligomerization. Informative, experimentally grounded self-association activity. Supporting Evidence: PMID:22072986 indicating that LZTFL1 forms homo-oligomers
GO:0042802 identical protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	ACCEPT	Summary: Self-binding (Q9NQ48 homodimer) from a large-scale interactome screen, corroborating the experimentally established homo-oligomerization. Reason: Consistent with directed homo-oligomerization data (PMID:22072986).
GO:0042802 identical protein binding	IPI PMID:27107012 Pooled-matrix protein interaction screens using Barcode Fusi...	ACCEPT	Summary: Self-binding (Q9NQ48 homodimer) from a barcode-fusion-genetics interaction screen, corroborating homo-oligomerization. Reason: Consistent with directed homo-oligomerization data (PMID:22072986).
GO:0042802 identical protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	ACCEPT	Summary: Self-binding (Q9NQ48 homodimer) from the HuRI reference binary interactome, corroborating homo-oligomerization. Reason: Consistent with directed homo-oligomerization data (PMID:22072986).
GO:0002177 manchette	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Electronic, mouse-orthology-based (ECO:0000265, from mouse Q9JHQ5) localization to the manchette, the transient spermatid microtubule structure. Plausible given strong testis expression and reported sperm-body localization of the rodent ortholog, but supported only by automated orthology transfer for the human protein. Falcon deep research corroborates the orthologous source observation: during mouse spermiogenesis the protein localizes to the developing flagellum and near the manchette at the elongated spermatid stage. Reason: Tissue/stage-specific localization inferred from the mouse ortholog; consistent with testis expression but not the core function and not directly demonstrated for human LZTFL1. The manchette-proximal localization is reported for the rodent ortholog (Huang 2021, summarized in the falcon deep research); kept non-core pending direct human evidence. Supporting Evidence: file:human/LZTFL1/LZTFL1-deep-research-falcon.md LZTFL1 localizes to the developing flagellum and appears near the manchette, a transient microtubule structure involved in sperm head shaping
GO:0005929 cilium	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: Electronic, mouse-orthology-based localization to cilium. As with the IBA cilium annotation, the primary human study found LZTFL1 is cytoplasmic and NOT enriched in cilia. Reason: Contradicted for the human protein by direct evidence of cytoplasmic, non-ciliary localization (PMID:22072986). Orthology transfer overstates ciliary residence.
GO:0044877 protein-containing complex binding	IEA GO_REF:0000107	ACCEPT	Summary: Electronic, mouse-orthology-based protein-containing complex binding, capturing the BBSome-binding activity. Well aligned with the experimentally established LZTFL1-BBSome interaction. Reason: Captures the biologically central BBSome-binding activity; corroborated by IDA (PMID:24550735) and the BBS9/BBSome co-purification in PMID:22072986.
GO:0005829 cytosol	IDA GO_REF:0000052	ACCEPT	Summary: Direct immunofluorescence (HPA) localization to cytosol, consistent with the experimentally established cytoplasmic distribution of LZTFL1. Reason: Supported by HPA IDA and by PMID:22072986 (cytoplasmic localization).
GO:1903565 negative regulation of protein localization to cilium	IMP PMID:22072986 A novel protein LZTFL1 regulates ciliary trafficking of the ...	ACCEPT	Summary: Direct mutant-phenotype evidence for the core function: LZTFL1 negatively regulates BBSome (BBS9/BBS4/BBS8) localization to the cilium. LZTFL1 depletion increases, and overexpression decreases, ciliary BBSome; effect is specific to the BBSome and not general IFT. Reason: Core function, directly demonstrated by loss/gain-of-function in PMID:22072986. Supporting Evidence: PMID:22072986 over-expression of wild-type LZTFL1 inhibited ciliary localization of BBS9
GO:1903568 negative regulation of protein localization to ciliary membrane	IMP PMID:22072986 A novel protein LZTFL1 regulates ciliary trafficking of the ...	ACCEPT	Summary: Direct mutant-phenotype evidence that LZTFL1 negatively regulates trafficking of membrane cargo (e.g. Smoothened) to the ciliary membrane via control of the BBSome. More specific sibling of the cilium term and captures the SMO/ciliary-membrane aspect. Reason: Supported by PMID:22072986: LZTFL1 suppresses SMO ciliary (membrane) localization. Core function. Supporting Evidence: PMID:22072986 LZTFL1 suppresses SMO localization to cilia
GO:0044877 protein-containing complex binding	IDA PMID:24550735 The centriolar satellite protein AZI1 interacts with BBS4 an...	ACCEPT	Summary: Direct experimental evidence for binding a protein-containing complex (the BBSome). Although this paper's title/abstract concern AZI1/CEP131, LZTFL1 was assayed as a BBSome-associated protein; the curator (UniProt) read the full text. This captures the central BBSome-binding activity of LZTFL1. Reason: Informative molecular function representing the experimentally established LZTFL1-BBSome (via BBS9) interaction; do not overrule an IDA on the basis of the abstract focus.
GO:0005829 cytosol	TAS Reactome:R-HSA-5624129	ACCEPT	Summary: Traceable-author (Reactome) cytosol localization, consistent with the experimentally established cytoplasmic/cytosolic distribution of LZTFL1. Reason: Consistent with HPA IDA cytosol and PMID:22072986 cytoplasmic localization.

Core Functions

Negative regulator of BBSome ciliary trafficking: LZTFL1 binds the BBSome in the cytoplasm and restrains its entry into (or promotes its retrieval from) the cilium, thereby controlling BBSome ciliary localization.

Molecular Function:

protein-containing complex binding

Directly Involved In:

negative regulation of protein localization to cilium

Supporting Evidence:

PMID:22072986
over-expression of wild-type LZTFL1 inhibited ciliary localization of BBS9
PMID:22072986
LZTFL1 is a specific regulator of BBSome ciliary trafficking but not general IFT

Regulation of ciliary trafficking of the Hedgehog transducer Smoothened (and hence Sonic hedgehog pathway responsiveness) through control of the BBSome, restraining SMO localization to the ciliary membrane.

Directly Involved In:

negative regulation of protein localization to ciliary membrane

Supporting Evidence:

PMID:22072986
LZTFL1 suppresses SMO localization to cilia

Self-association into homo-oligomers, which is part of how LZTFL1 assembles to engage the BBSome (via the subunit BBS9).

Molecular Function:

identical protein binding

Supporting Evidence:

PMID:22072986
indicating that LZTFL1 forms homo-oligomers

References

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000052

Gene Ontology annotation based on curation of immunofluorescence data

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:22072986

A novel protein LZTFL1 regulates ciliary trafficking of the BBSome and Smoothened.

LZTFL1 is a cytoplasmic protein (not enriched in cilia/basal body) that binds the BBSome via BBS9, self-associates into homo-oligomers, and negatively regulates BBSome and Smoothened ciliary trafficking; it acts specifically on the BBSome, not general IFT.

PMID:24550735

The centriolar satellite protein AZI1 interacts with BBS4 and regulates ciliary trafficking of the BBSome.

Study of AZI1/CEP131 as a BBSome-trafficking regulator in which LZTFL1 was assayed as a BBSome-associated protein, supporting the IDA protein-containing complex binding annotation.

PMID:25416956

A proteome-scale map of the human interactome network.

PMID:27107012

Pooled-matrix protein interaction screens using Barcode Fusion Genetics.

PMID:27173435

An organelle-specific protein landscape identifies novel diseases and molecular mechanisms.

PMID:28514442

Architecture of the human interactome defines protein communities and disease networks.

PMID:31515488

Extensive disruption of protein interactions by genetic variants across the allele frequency spectrum in human populations.

PMID:32296183

A reference map of the human binary protein interactome.

PMID:33961781

Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.

Reactome:R-HSA-5624129

LZTFL1 binds the BBSome and prevents its traffic to the cilium

file:human/LZTFL1/LZTFL1-deep-research-falcon.md

Falcon deep research report for LZTFL1

LZTFL1-specific findings: physical interaction with IFT27 (yeast two-hybrid, co-IP, colocalization, luciferase complementation; Huang 2021); direct binding to AP-1 (beta1) and AP-2 (beta2) via a conserved DxxFxxLxxxR motif with participation in TfR1 trafficking (Promchan 2020); and stage-specific testis localization to the developing flagellum and near the manchette during spermiogenesis (Huang 2021).

Suggested Experiments

Experiment: Live-cell imaging of tagged BBSome subunits with acute LZTFL1 degradation (e.g. auxin-inducible degron) to distinguish whether LZTFL1 controls ciliary entry vs. retrieval/exit kinetics.

Experiment: Structural/biochemical mapping of the LZTFL1 N-terminal regulatory region (including the conserved K24/R25 basic motif whose mutation is dominant-negative) to identify the effector that links BBSome binding to inhibition of ciliary entry.

Experiment: Generate LZTFL1-null vs. BBS17 patient-variant (e.g. L87P) knock-in cells/organoids and quantify BBSome and SMO ciliary dynamics plus SHH target-gene output to relate molecular defect to disease.

Deep Research

Falcon

(LZTFL1-deep-research-falcon.md)

Comprehensive Research Report: LZTFL1 (Leucine Zipper Transcription Factor-Like Protein 1) Falcon Edison Scientific Literature 23 citations 1 artifacts 2026-06-20T07:15:36.291036

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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: LZTFL1 (Leucine Zipper Transcription Factor-Like Protein 1)

Gene Identity and Overview

LZTFL1 (UniProt: Q9NQ48), also designated as BBS17 (Bardet-Biedl Syndrome 17), encodes leucine zipper transcription factor-like protein 1 in humans (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 7-11). The protein belongs to the LZTFL1 family and contains key domains including a leucine zipper motif and the IPR026157 (LZTFL1) domain (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 2-4). The gene is located at chromosomal position 3p21.3, a region frequently deleted in various cancers (huang2021leucinezippertranscription pages 7-11). LZTFL1 has emerged as a critical regulator of ciliary protein trafficking and has been implicated in Bardet-Biedl syndrome, a multisystem ciliopathy (melluso2023bardetbiedlsyndromecurrent pages 6-8, huang2021leucinezippertranscription pages 7-11).

Primary Molecular Function

Unlike typical transcription factors suggested by its name, LZTFL1 does not function as an enzyme or a nuclear transcription regulator under normal physiological conditions (promchan2020leucinezippertranscription pages 1-2, huang2021leucinezippertranscription pages 7-11, huang2021leucinezippertranscription pages 11-15). Instead, LZTFL1 serves as a regulatory adapter protein with two distinct but related molecular functions: regulation of ciliary BBSome trafficking and clathrin-mediated membrane protein trafficking.

Ciliary BBSome Regulation

LZTFL1 functions as a negative regulator of BBSome entry into primary cilia (wingfield2018traffickingofciliary pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2). The BBSome is an octameric protein complex composed of eight Bardet-Biedl syndrome proteins that acts as a cargo adapter for intraflagellar transport (IFT) of ciliary membrane proteins (wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2). LZTFL1 physically interacts with IFT27, a component of the IFT-B complex, as demonstrated by yeast two-hybrid screening, co-immunoprecipitation, colocalization studies, and luciferase complementation assays (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 7-11, huang2021leucinezippertranscription pages 11-15). This interaction is functionally significant: in the absence of LZTFL1, the BBSome accumulates abnormally within cilia, and ciliary export of G-protein coupled receptors (GPCRs) including GPR161 and Smoothened is impaired (wingfield2018traffickingofciliary pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5).

The molecular mechanism involves coordination between LZTFL1, IFT27, and the IFT-B complex. Recent studies show that IFT25-IFT27 and the RABL2 GTPase bind the IFT74-IFT81 dimer of the IFT-B complex in a mutually exclusive manner (zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2). GTP-locked RABL2 phenocopies IFT27-knockout cells, causing accumulation of LZTFL1 and the BBSome within cilia and suppression of ciliary GPCR export (zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2). These findings suggest that LZTFL1 mediates the coupling between the BBSome and the IFT machinery, controlling when and how the BBSome enters and exits cilia.

Clathrin Adaptor-Mediated Trafficking

LZTFL1 directly binds to the β1 subunit of adaptor protein complex-1 (AP-1) and the β2 subunit of AP-2, as demonstrated by in vitro pull-down assays using purified proteins (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9). This binding is mediated by a conserved DxxFxxLxxxR motif in LZTFL1, which is recognized by the platform subdomain of AP-1 and AP-2 β subunits (promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9). Mutagenesis of this motif abolishes binding to both AP-1 and AP-2 (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 7-9).

LZTFL1 participates in the trafficking of transferrin receptor 1 (TfR1), a well-characterized cargo of AP-1 and AP-2 complexes (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 14-17, promchan2020leucinezippertranscription pages 11-14). While LZTFL1 co-immunoprecipitates with TfR1 from cell lysates, purified protein studies demonstrate that this interaction is indirect, occurring through AP-1 or AP-2 complexes rather than through direct LZTFL1-TfR1 binding (promchan2020leucinezippertranscription pages 14-17). In LZTFL1-knockout HeLa cells, the cell surface level of TfR1 is reduced by approximately 40-50% compared to wild-type cells, and the rate of TfR1 internalization is significantly decreased (promchan2020leucinezippertranscription pages 14-17). Importantly, this effect appears specific to TfR1, as LZTFL1 knockout does not affect cell surface levels of epidermal growth factor receptor (EGFR) or cation-independent mannose 6-phosphate receptor (CI-MPR) (promchan2020leucinezippertranscription pages 14-17), indicating selective regulation rather than a global trafficking defect.

Subcellular Localization

LZTFL1 exhibits multiple subcellular localizations consistent with its diverse trafficking functions (promchan2020leucinezippertranscription pages 1-2, huang2021leucinezippertranscription pages 7-11, huang2021leucinezippertranscription pages 11-15, promchan2020leucinezippertranscription pages 11-14). The protein is predominantly cytoplasmic, with enrichment in the perinuclear region (PNR) encompassing the trans-Golgi network (TGN) and peripheral endosomal compartments (promchan2020leucinezippertranscription pages 11-14). Immunofluorescence studies show strong colocalization of LZTFL1 with AP-1 in both the PNR and cytoplasm (promchan2020leucinezippertranscription pages 11-14). The localization of LZTFL1 in the PNR is ADP-ribosylation factor (Arf)-dependent, as demonstrated by brefeldin A (BFA) treatment experiments: brief BFA exposure disperses both LZTFL1 and AP-1 from the PNR, and both proteins relocalize together during recovery from BFA washout (promchan2020leucinezippertranscription pages 11-14). Furthermore, siRNA-mediated knockdown of AP-1 significantly reduces LZTFL1 levels in the PNR without affecting total cellular LZTFL1, indicating that AP-1 plays a role in recruiting or maintaining LZTFL1 at this location (promchan2020leucinezippertranscription pages 11-14).

LZTFL1 also localizes to primary cilia, where it regulates BBSome trafficking and ciliary protein composition (wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5). In specialized ciliated cells, such as photoreceptors and spermatids, LZTFL1 shows tissue-specific localization patterns. During spermatogenesis in mouse testis, LZTFL1 protein expression begins at the round spermatid stage with a vesicular cytoplasmic distribution pattern (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 11-15). At the elongated spermatid stage, LZTFL1 localizes to the developing flagellum and appears near the manchette, a transient microtubule structure involved in sperm head shaping (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 11-15). LZTFL1 is not detected in the nucleus under normal conditions, consistent with its non-transcriptional function (promchan2020leucinezippertranscription pages 1-2, huang2021leucinezippertranscription pages 7-11, huang2021leucinezippertranscription pages 11-15).

Biological Pathways and Signaling Networks

Intraflagellar Transport and Ciliogenesis

LZTFL1 plays a central role in the IFT pathway, which is essential for the assembly and maintenance of cilia and flagella (wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2). IFT involves the bidirectional movement of protein complexes (IFT particles) along the ciliary axoneme, powered by kinesin-2 motors for anterograde transport and dynein-2 for retrograde transport (nakayama2018ciliaryproteintrafficking pages 1-2). The IFT-B complex mediates anterograde trafficking, while the BBSome functions as an adapter for membrane protein trafficking within cilia (wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2).

LZTFL1 regulates BBSome-mediated export of ciliary membrane proteins (wingfield2018traffickingofciliary pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2). The current model suggests that LZTFL1 acts as a negative regulator that prevents premature or inappropriate BBSome entry into cilia (wingfield2018traffickingofciliary pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2). When IFT27 is absent or when RABL2 is locked in its GTP-bound state, LZTFL1 and the BBSome accumulate within cilia, impairing the export of ciliary GPCRs such as GPR161 and Smoothened (zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5). This dysregulation leads to abnormal ciliary signaling and is associated with ciliopathy phenotypes (wingfield2018traffickingofciliary pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2).

Loss of LZTFL1 affects cilia structure and function. Lztfl1-knockout mouse embryonic fibroblasts (MEFs) have significantly longer cilia than wild-type MEFs (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 7-11). Global Lztfl1 knockout mice exhibit abnormal cilia development in multiple tissues (huang2021leucinezippertranscription pages 7-11). In photoreceptor cells of Lztfl1-knockout mice, AP-1 distribution is abnormal, and multiple outer segment proteins are mislocalized (promchan2020leucinezippertranscription pages 1-2). These findings demonstrate that LZTFL1 is required for proper ciliary protein composition and ciliary function.

Hedgehog Signaling Pathway

Through its role in ciliary trafficking, LZTFL1 influences Hedgehog (Hh) signaling, a crucial developmental pathway in vertebrates (zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5). In the Hh pathway, Smoothened (Smo) accumulation in cilia is required for pathway activation, while GPR161 must be removed from cilia for full pathway activation (zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5). IFT27, the binding partner of LZTFL1, is extensively involved in Hh signaling: unlike most IFT proteins, IFT27 is dispensable for cilia formation but critically affects Hh signaling (eguether2018intraflagellartransportis pages 1-5). Ift27 mutant cells show defects in ciliary localization of the BBSome and LZTFL1, leading to impaired Hh pathway function (eguether2018intraflagellartransportis pages 1-5). Specifically, loss of IFT27 affects the trafficking and ciliary tip localization of Gli transcription factors, Kif7, and SuFu, which are key downstream effectors of Hh signaling (eguether2018intraflagellartransportis pages 1-5). These studies position LZTFL1 as an important regulator of Hh signaling through its control of BBSome-mediated trafficking.

Epithelial-Mesenchymal Transition and Cancer

LZTFL1 functions as a suppressor of epithelial-mesenchymal transition (EMT), a process crucial for cancer metastasis (downes2021identificationoflztfl1 pages 1-2, wang2019microrna21promotesbreast pages 1-2, downes2021identificationoflztfl1 pages 3-4). In breast cancer, LZTFL1 has been identified as a direct target of microRNA-21 (miR-21) (wang2019microrna21promotesbreast pages 1-2). miR-21 is upregulated in breast cancer and promotes cancer proliferation and metastasis by targeting LZTFL1 (wang2019microrna21promotesbreast pages 1-2). Inhibition of miR-21 increases LZTFL1 expression, which suppresses cell proliferation, migration, and the expression of EMT markers in breast cancer cells (wang2019microrna21promotesbreast pages 1-2). Conversely, knockdown of LZTFL1 overcomes the suppressive effects of miR-21 inhibitors on cell proliferation, metastasis, and EMT marker expression (wang2019microrna21promotesbreast pages 1-2). In vivo studies using nude mice demonstrated that miR-21 overexpression promotes breast tumor growth and metastasis, accompanied by decreased LZTFL1 expression and increased EMT marker expression (wang2019microrna21promotesbreast pages 1-2).

Recent work on COVID-19 genetic risk factors has provided additional insight into LZTFL1's role in EMT. A genome-wide association study identified the 3p21.31 locus as conferring a twofold increased risk of respiratory failure from COVID-19 (downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4). Using a combined multiomics and machine learning approach, researchers identified LZTFL1 as the likely effector gene at this locus (downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4). The risk-associated genetic variant (rs17713054) acts as a gain-of-function enhancer that upregulates LZTFL1 expression in pulmonary epithelial cells (downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4). Spatial transcriptomic analysis of lung biopsies from COVID-19 patients showed signals associated with EMT in ciliated epithelial cells, which are major targets for SARS-CoV-2 infection (downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4). These findings suggest that LZTFL1 regulates EMT in pulmonary epithelial cells during viral infection, and that increased LZTFL1 expression may promote pathological EMT contributing to severe COVID-19 outcomes (downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4, pi2023molecularmechanismsof pages 8-9).

Other Biological Roles

LZTFL1 has been implicated in immune synapse formation in activated T cells, where it associates with the immune synapse and may participate in T cell activation processes (promchan2020leucinezippertranscription pages 1-2). In the male reproductive system, LZTFL1 is required for normal sperm function and male fertility (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 7-11, huang2021leucinezippertranscription pages 11-15). Lztfl1-knockout male mice exhibit significantly reduced fertility associated with low sperm motility and high levels of abnormal sperm, a condition termed astheno-teratozoospermia (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 7-11, huang2021leucinezippertranscription pages 11-15). In vitro fertilization assays reveal reduced fertilization rates and impaired embryonic development when using sperm from Lztfl1-knockout mice (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 11-15). These reproductive defects likely result from abnormal flagellum formation, as LZTFL1 localizes to developing flagella in elongating spermatids (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 11-15).

Structural Features and Functional Domains

LZTFL1 contains several conserved structural motifs that are critical for its function (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9). The most functionally important is the DxxFxxLxxxR motif (where x represents any amino acid), which is essential for binding to the β subunits of AP-1 and AP-2 (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9). This motif is highly conserved across vertebrate LZTFL1 orthologs (promchan2020leucinezippertranscription pages 2-4). Mutation of this motif abolishes direct binding to AP-1 and AP-2 in vitro and disrupts the indirect association with TfR1 in cells (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 7-9, promchan2020leucinezippertranscription pages 14-17). LZTFL1 also contains a leucine zipper motif, a SNARE domain, and a coiled-coil domain, though the precise functions of these additional domains remain less well characterized (promchan2020leucinezippertranscription pages 2-4). The N-terminal region (amino acids 11-146) appears important for certain functions, as deletion of this region (ΔNT mutant) affects protein behavior in cellular assays (promchan2020leucinezippertranscription pages 7-9).

Disease Associations

Biallelic loss-of-function mutations in LZTFL1 cause Bardet-Biedl syndrome type 17 (BBS17), a rare autosomal recessive ciliopathy (huang2021leucinezippertranscription pages 1-7, melluso2023bardetbiedlsyndromecurrent pages 6-8, huang2021leucinezippertranscription pages 7-11). BBS is characterized by multiple clinical features including retinal degeneration, obesity, polydactyly, renal abnormalities, learning difficulties, and hypogonadism (melluso2023bardetbiedlsyndromecurrent pages 6-8). Patients with LZTFL1 mutations display typical BBS phenotypes, though mesoaxial polydactyly may be more specifically associated with BBS17 (melluso2023bardetbiedlsyndromecurrent pages 6-8). The global Lztfl1-knockout mouse model recapitulates several BBS features, including obesity, retinal degeneration, and abnormal cilia development (huang2021leucinezippertranscription pages 7-11). Currently, at least 26 genes have been associated with BBS, with LZTFL1 being designated as BBS17 (melluso2023bardetbiedlsyndromecurrent pages 6-8).

Beyond BBS, LZTFL1 has been implicated in cancer as a tumor suppressor, with the 3p21.3 locus frequently deleted in various cancers (huang2021leucinezippertranscription pages 7-11). Recent genetic studies have identified LZTFL1 as a candidate effector gene at the 3p21.31 COVID-19 risk locus, where genetic variants that increase LZTFL1 expression in lung epithelial cells are associated with increased risk of severe COVID-19 and respiratory failure (downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4). This represents a unique situation where gain of LZTFL1 function, rather than loss of function, may contribute to disease pathology (downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4).

Summary

LZTFL1 is a multifunctional regulatory adapter protein that coordinates protein trafficking in two major cellular contexts: ciliary BBSome-mediated trafficking and clathrin adaptor-mediated endocytosis. Through its interaction with IFT27 and the IFT-B complex, LZTFL1 negatively regulates BBSome entry into cilia and controls ciliary GPCR export, thereby influencing ciliary signaling pathways including Hedgehog signaling. Through direct binding to AP-1 and AP-2 via its DxxFxxLxxxR motif, LZTFL1 regulates trafficking of specific membrane proteins such as TfR1. LZTFL1 also suppresses EMT in epithelial cells and cancer. Loss of LZTFL1 function causes Bardet-Biedl syndrome, a multisystem ciliopathy, while dysregulation of LZTFL1 expression has been implicated in cancer and severe COVID-19. The protein primarily functions in the cytoplasm, at the trans-Golgi network, and within primary cilia, where its trafficking regulatory activities are executed.

Table: This table summarizes the main experimentally supported functions, binding partners, localization, pathways, and disease-relevant evidence for human LZTFL1. It is useful as a compact evidence map linking molecular mechanism to cell biology and phenotype.

References

(huang2021leucinezippertranscription pages 1-7): Qian Huang, Wei Li, Qi Zhou, Parirokh Awasthi, Caroline Cazin, Yitian Yap, Ljiljana Mladenovic-Lucas, Bo Hu, Pancharatnam Jeyasuria, Ling Zhang, James G. Granneman, Rex A. Hess, Pierre F. Ray, Zine-Eddine Kherraf, Ven Natarajan, and Zhibing Zhang. Leucine zipper transcription factor-like 1 (lztfl1), an intraflagellar transporter protein 27 (ift27) associated protein, is required for normal sperm function and male fertility. Sep 2021. URL: https://doi.org/10.1016/j.ydbio.2021.05.006, doi:10.1016/j.ydbio.2021.05.006. This article has 22 citations and is from a peer-reviewed journal.
(huang2021leucinezippertranscription pages 7-11): Qian Huang, Wei Li, Qi Zhou, Parirokh Awasthi, Caroline Cazin, Yitian Yap, Ljiljana Mladenovic-Lucas, Bo Hu, Pancharatnam Jeyasuria, Ling Zhang, James G. Granneman, Rex A. Hess, Pierre F. Ray, Zine-Eddine Kherraf, Ven Natarajan, and Zhibing Zhang. Leucine zipper transcription factor-like 1 (lztfl1), an intraflagellar transporter protein 27 (ift27) associated protein, is required for normal sperm function and male fertility. Sep 2021. URL: https://doi.org/10.1016/j.ydbio.2021.05.006, doi:10.1016/j.ydbio.2021.05.006. This article has 22 citations and is from a peer-reviewed journal.
(promchan2020leucinezippertranscription pages 1-2): Kanyarat Promchan and Ven Natarajan. Leucine zipper transcription factor-like 1 binds adaptor protein complex-1 and 2 and participates in trafficking of transferrin receptor 1. PLoS ONE, 15:e0226298, Jan 2020. URL: https://doi.org/10.1371/journal.pone.0226298, doi:10.1371/journal.pone.0226298. This article has 13 citations and is from a peer-reviewed journal.
(promchan2020leucinezippertranscription pages 2-4): Kanyarat Promchan and Ven Natarajan. Leucine zipper transcription factor-like 1 binds adaptor protein complex-1 and 2 and participates in trafficking of transferrin receptor 1. PLoS ONE, 15:e0226298, Jan 2020. URL: https://doi.org/10.1371/journal.pone.0226298, doi:10.1371/journal.pone.0226298. This article has 13 citations and is from a peer-reviewed journal.
(melluso2023bardetbiedlsyndromecurrent pages 6-8): Andrea Melluso, Floriana Secondulfo, Giovanna Capolongo, Giovambattista Capasso, and Miriam Zacchia. Bardet-biedl syndrome: current perspectives and clinical outlook. Therapeutics and Clinical Risk Management, 19:115-132, Jan 2023. URL: https://doi.org/10.2147/tcrm.s338653, doi:10.2147/tcrm.s338653. This article has 107 citations and is from a peer-reviewed journal.
(huang2021leucinezippertranscription pages 11-15): Qian Huang, Wei Li, Qi Zhou, Parirokh Awasthi, Caroline Cazin, Yitian Yap, Ljiljana Mladenovic-Lucas, Bo Hu, Pancharatnam Jeyasuria, Ling Zhang, James G. Granneman, Rex A. Hess, Pierre F. Ray, Zine-Eddine Kherraf, Ven Natarajan, and Zhibing Zhang. Leucine zipper transcription factor-like 1 (lztfl1), an intraflagellar transporter protein 27 (ift27) associated protein, is required for normal sperm function and male fertility. Sep 2021. URL: https://doi.org/10.1016/j.ydbio.2021.05.006, doi:10.1016/j.ydbio.2021.05.006. This article has 22 citations and is from a peer-reviewed journal.
(wingfield2018traffickingofciliary pages 1-2): Jenna L. Wingfield, Karl-Ferdinand Lechtreck, and Esben Lorentzen. Trafficking of ciliary membrane proteins by the intraflagellar transport/bbsome machinery. Essays in biochemistry, 62 6:753-763, Oct 2018. URL: https://doi.org/10.1042/ebc20180030, doi:10.1042/ebc20180030. This article has 183 citations and is from a peer-reviewed journal.
(zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2): Zhuang Zhou, Yohei Katoh, and Kazuhisa Nakayama. Cep19–rabl2–ift-b axis controls bbsome-mediated ciliary gpcr export. Molecular Biology of the Cell, Nov 2022. URL: https://doi.org/10.1091/mbc.e22-05-0161, doi:10.1091/mbc.e22-05-0161. This article has 10 citations and is from a domain leading peer-reviewed journal.
(nakayama2018ciliaryproteintrafficking pages 1-2): Kazuhisa Nakayama and Yohei Katoh. Ciliary protein trafficking mediated by ift and bbsome complexes with the aid of kinesin-2 and dynein-2 motors. Journal of biochemistry, 163 3:155-164, Mar 2018. URL: https://doi.org/10.1093/jb/mvx087, doi:10.1093/jb/mvx087. This article has 160 citations and is from a peer-reviewed journal.
(eguether2018intraflagellartransportis pages 1-5): Thibaut Eguether, Fabrice P. Cordelieres, and Gregory J. Pazour. Intraflagellar transport is deeply integrated in hedgehog signaling. Molecular Biology of the Cell, 29:1178-1189, May 2018. URL: https://doi.org/10.1091/mbc.e17-10-0600, doi:10.1091/mbc.e17-10-0600. This article has 65 citations and is from a domain leading peer-reviewed journal.
(promchan2020leucinezippertranscription pages 7-9): Kanyarat Promchan and Ven Natarajan. Leucine zipper transcription factor-like 1 binds adaptor protein complex-1 and 2 and participates in trafficking of transferrin receptor 1. PLoS ONE, 15:e0226298, Jan 2020. URL: https://doi.org/10.1371/journal.pone.0226298, doi:10.1371/journal.pone.0226298. This article has 13 citations and is from a peer-reviewed journal.
(promchan2020leucinezippertranscription pages 14-17): Kanyarat Promchan and Ven Natarajan. Leucine zipper transcription factor-like 1 binds adaptor protein complex-1 and 2 and participates in trafficking of transferrin receptor 1. PLoS ONE, 15:e0226298, Jan 2020. URL: https://doi.org/10.1371/journal.pone.0226298, doi:10.1371/journal.pone.0226298. This article has 13 citations and is from a peer-reviewed journal.
(promchan2020leucinezippertranscription pages 11-14): Kanyarat Promchan and Ven Natarajan. Leucine zipper transcription factor-like 1 binds adaptor protein complex-1 and 2 and participates in trafficking of transferrin receptor 1. PLoS ONE, 15:e0226298, Jan 2020. URL: https://doi.org/10.1371/journal.pone.0226298, doi:10.1371/journal.pone.0226298. This article has 13 citations and is from a peer-reviewed journal.
(downes2021identificationoflztfl1 pages 1-2): Damien J. Downes, Amy R. Cross, Peng Hua, Nigel Roberts, Ron Schwessinger, Antony J. Cutler, Altar M. Munis, Jill Brown, Olga Mielczarek, Carlos E. de Andrea, Ignacio Melero, Deborah R. Gill, Stephen C. Hyde, Julian C. Knight, John A. Todd, Stephen N. Sansom, Fadi Issa, James O. J. Davies, and Jim R. Hughes. Identification of lztfl1 as a candidate effector gene at a covid-19 risk locus. Nature Genetics, 53:1606-1615, Nov 2021. URL: https://doi.org/10.1038/s41588-021-00955-3, doi:10.1038/s41588-021-00955-3. This article has 198 citations and is from a highest quality peer-reviewed journal.
(wang2019microrna21promotesbreast pages 1-2): Hui Wang, Zheqiong Tan, Hui Hu, Hongzhou Liu, Tangwei Wu, Chao Zheng, Xiuling Wang, Zhenzhao Luo, Jing Wang, Shuiyi Liu, Zhongxin Lu, and Jiancheng Tu. Microrna-21 promotes breast cancer proliferation and metastasis by targeting lztfl1. BMC Cancer, Jul 2019. URL: https://doi.org/10.1186/s12885-019-5951-3, doi:10.1186/s12885-019-5951-3. This article has 343 citations and is from a peer-reviewed journal.
(downes2021identificationoflztfl1 pages 3-4): Damien J. Downes, Amy R. Cross, Peng Hua, Nigel Roberts, Ron Schwessinger, Antony J. Cutler, Altar M. Munis, Jill Brown, Olga Mielczarek, Carlos E. de Andrea, Ignacio Melero, Deborah R. Gill, Stephen C. Hyde, Julian C. Knight, John A. Todd, Stephen N. Sansom, Fadi Issa, James O. J. Davies, and Jim R. Hughes. Identification of lztfl1 as a candidate effector gene at a covid-19 risk locus. Nature Genetics, 53:1606-1615, Nov 2021. URL: https://doi.org/10.1038/s41588-021-00955-3, doi:10.1038/s41588-021-00955-3. This article has 198 citations and is from a highest quality peer-reviewed journal.
(pi2023molecularmechanismsof pages 8-9): Peng Pi, Zhipeng Zeng, Liqing Zeng, Bing Han, Xizhe Bai, and Shousheng Xu. Molecular mechanisms of covid-19-induced pulmonary fibrosis and epithelial-mesenchymal transition. Frontiers in Pharmacology, Aug 2023. URL: https://doi.org/10.3389/fphar.2023.1218059, doi:10.3389/fphar.2023.1218059. This article has 28 citations.

Artifacts

Edison artifact artifact-00

Citations

huang2021leucinezippertranscription pages 7-11
promchan2020leucinezippertranscription pages 14-17
promchan2020leucinezippertranscription pages 11-14
nakayama2018ciliaryproteintrafficking pages 1-2
promchan2020leucinezippertranscription pages 1-2
eguether2018intraflagellartransportis pages 1-5
promchan2020leucinezippertranscription pages 2-4
promchan2020leucinezippertranscription pages 7-9
melluso2023bardetbiedlsyndromecurrent pages 6-8
huang2021leucinezippertranscription pages 1-7
huang2021leucinezippertranscription pages 11-15
wingfield2018traffickingofciliary pages 1-2
pi2023molecularmechanismsof pages 8-9
https://doi.org/10.1016/j.ydbio.2021.05.006,
https://doi.org/10.1371/journal.pone.0226298,
https://doi.org/10.2147/tcrm.s338653,
https://doi.org/10.1042/ebc20180030,
https://doi.org/10.1091/mbc.e22-05-0161,
https://doi.org/10.1093/jb/mvx087,
https://doi.org/10.1091/mbc.e17-10-0600,
https://doi.org/10.1038/s41588-021-00955-3,
https://doi.org/10.1186/s12885-019-5951-3,
https://doi.org/10.3389/fphar.2023.1218059,

📚 Additional Documentation

Notes

(LZTFL1-notes.md)

LZTFL1 (BBS17) — Gene Review Notes

UniProt: Q9NQ48 | HGNC:6741 | GeneID 54585 | 299 aa | Chr 3p21.3

Summary of function

LZTFL1 ("Leucine zipper transcription factor-like protein 1") is, despite its name, a
cytoplasmic, predominantly alpha-helical / coiled-coil protein and NOT a transcription
factor. It is a negative regulator of the ciliary trafficking of the BBSome (the
seven-subunit BBS protein complex) and, through the BBSome, of Smoothened (SMO) ciliary
localization and Sonic hedgehog (SHH) signaling. Loss-of-function mutations cause
Bardet–Biedl syndrome type 17 (BBS17).

Key evidence

PMID:22072986 (Seo et al. 2011, PLoS Genet) — the foundational functional paper (full text available)

LZTFL1 identified as a BBSome-interacting protein by TAP of LAP-BBS4 from mouse testis
PMID:22072986.
Interacts with the BBSome specifically through BBS9; C-terminal half (aa 145–299) of
LZTFL1 binds BBS9 PMID:22072986.
Self-associates / homo-oligomerizes PMID:22072986.
Cytoplasmic, NOT enriched in cilia or basal body PMID:22072986. LZTFL1–BBSome interaction occurs in the cytoplasm (in situ PLA).
Only a subset of LZTFL1 associates with the BBSome; it is not a constitutive component
PMID:22072986.
Negative regulation of BBSome ciliary entry: knockdown increases ciliary BBS9/BBS4/BBS8;
overexpression inhibits ciliary BBS9 PMID:22072986. KR→AS mutation at aa 24-25 acts as dominant negative, increasing BBSome ciliary localization.
Specific to the BBSome, not general IFT PMID:22072986.
LZTFL1 depletion restores BBSome ciliary trafficking in BBS3/BBS5-depleted cells.
SMO / SHH: LZTFL1 suppresses SMO ciliary localization PMID:22072986; BBSome facilitates SMO ciliary localization. Contributes to SHH responsiveness.

PMID:22510444 (Marion et al. 2012, J Med Genet) — disease/BBS17 (abstract/UniProt only)

Exome sequencing identified LZTFL1 mutations in BBS family with situs inversus and
insertional polydactyly; established LZTFL1 = BBS17 and role in SHH/SMO trafficking.

PMID:23692385 (Schaefer et al. 2014) — mesoaxial polydactyly major feature in BBS17; variant L87P.

PMID:24550735 (Chamling et al. 2014, PLoS Genet) — AZI1/CEP131 paper (abstract only; full_text_available: false)

About AZI1/CEP131 regulating BBSome trafficking, but the GOA IDA annotation
GO:0044877 protein-containing complex binding on LZTFL1 (PMID:24550735, assigned by UniProt)
derives from LZTFL1 being assayed as a BBSome-associated protein in this study. Curator read
full text; defer.

Protein-interaction (IPI) annotations

GO:0005515 protein binding and GO:0042802 identical protein binding come from large-scale
interactome / IntAct datasets (PMID:25416956, 27107012, 27173435, 28514442, 31515488,
32296183, 33961781). WITH/FROM partners include BBS9 (Q3SYG4), SDCBP/syntenin (O00560),
proteasome subunits (PSMA1 P25786, PSMB1 P20618), self (Q9NQ48), etc. GO:0042802 (self-binding)
is well-supported by the directed homo-oligomerization data in PMID:22072986.

Localization

UniProt SUBCELLULAR LOCATION: Cytoplasm (PMID:20233871, PMID:22072986). KW: Cytoplasm.
GO:0005829 cytosol IDA (HPA, GO_REF:0000052) and TAS (Reactome) — well supported.
GO:0005737 cytoplasm — supported.
GO:0005929 cilium (IBA + IEA orthology) — LZTFL1 is NOT enriched in cilia per the primary
functional study; it acts in the cytoplasm. Cilium location is questionable/over-annotated
for the human protein, but it acts upon ciliary trafficking; "is_active_in cilium" IBA is weak.
GO:0002177 manchette (IEA, ECO:0000265 from mouse Q9JHQ5) — spermatid microtubule structure;
plausible (testis expression, sperm body localization) but orthology-electronic only.

Tumor-suppressor / other (NOT in GOA being reviewed)

PMID:20233871 proposed tumor-suppressor function (3p21.3 deletion region); UniProt notes
"May have tumor suppressor function" and "May play a role in neurite outgrowth" — speculative,
not in the annotation set under review.
COVID-19 severity GWAS locus at 3p21.31 (largely genomic/regulatory, separate from ciliary
protein function). Not a GO molecular/cellular function annotation; out of scope.

Core function synthesis

Negative regulator of BBSome ciliary trafficking (cytoplasmic): GO:1903565 / GO:1903568.
BBSome binding (via BBS9) — protein-containing complex binding GO:0044877; mediator of
BBSome ciliary localization control.
Self-association / homo-oligomerization — GO:0042802.
Downstream: regulation of SMO ciliary trafficking / SHH signaling responsiveness.

📄 View Raw YAML

id: Q9NQ48
gene_symbol: LZTFL1
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  LZTFL1 (Leucine zipper transcription factor-like protein 1; also BBS17) is a cytoplasmic,
  predominantly alpha-helical coiled-coil protein that, despite its name, is not a transcription
  factor. It functions as a negative regulator of the ciliary trafficking of the BBSome, the
  eight-subunit Bardet-Biedl syndrome protein complex that delivers membrane cargo to and from
  the primary cilium. LZTFL1 binds the BBSome in the cytoplasm through the BBSome subunit BBS9
  and restrains BBSome entry into (or promotes its retrieval from) the cilium; only a subset of
  the cellular LZTFL1 pool is BBSome-associated and it is not a constitutive structural subunit.
  Through its control of BBSome ciliary localization, LZTFL1 regulates the ciliary trafficking of
  the Hedgehog signal transducer Smoothened (SMO) and thereby contributes to Sonic hedgehog
  pathway responsiveness. LZTFL1 self-associates into homo-oligomers. It is broadly expressed,
  including in testis, where the rodent ortholog has been localized to the spermatid
  manchette/sperm cell body. Loss-of-function mutations in LZTFL1 cause Bardet-Biedl syndrome
  type 17, characterized by retinopathy, obesity, polydactyly (often mesoaxial), renal anomalies,
  and sometimes situs inversus.
alternative_products:
- name: '1'
  id: Q9NQ48-1
- name: '2'
  id: Q9NQ48-2
  sequence_note: VSP_053429
- name: '3'
  id: Q9NQ48-3
  sequence_note: VSP_053428, VSP_053430
existing_annotations:
- term:
    id: GO:0005929
    label: cilium
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Phylogenetic (IBA) localization to cilium. The primary functional study explicitly found
      that LZTFL1 is cytoplasmic and is NOT enriched in cilia or basal bodies; it acts on the
      BBSome in the cytoplasm to regulate ciliary entry. LZTFL1 acts upon ciliary trafficking
      but is not itself a ciliary-resident protein, so "is_active_in cilium" overstates its
      localization.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      PMID:22072986 directly shows LZTFL1 is cytoplasmic without ciliary/centriolar enrichment,
      and that the LZTFL1-BBSome interaction occurs in the cytoplasm. The cytosol/cytoplasm
      annotations better capture where it acts.
- term:
    id: GO:0030317
    label: flagellated sperm motility
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic inference of a role in flagellated sperm motility. LZTFL1 is highly expressed
      in testis, the mouse ortholog localizes to the sperm flagellum/manchette region, and BBS
      proteins are required for sperm flagella; a contribution to sperm function is plausible but
      is a peripheral, tissue-specific role rather than the core molecular activity of the protein.
      Falcon deep research summarizes mouse knockout data (Huang 2021) in which Lztfl1-null males
      have reduced fertility with low sperm motility and abnormal sperm (astheno-teratozoospermia),
      consistent with this process annotation (in the rodent ortholog).
    action: KEEP_AS_NON_CORE
    reason: >-
      Consistent with testis expression and the BBS/ciliopathy context, and corroborated by the
      mouse-ortholog knockout sperm-motility phenotype summarized in the falcon deep research, but
      this is a downstream/tissue-specific process, not the core BBSome-trafficking-regulator
      function. Retain as non-core.
    supported_by:
    - reference_id: file:human/LZTFL1/LZTFL1-deep-research-falcon.md
      supporting_text: >-
        Lztfl1-knockout male mice exhibit significantly reduced fertility associated with low
        sperm motility and high levels of abnormal sperm, a condition termed
        astheno-teratozoospermia
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Phylogenetic localization to cytoplasm, consistent with direct experimental evidence that
      LZTFL1 is a cytoplasmic protein that binds and regulates the BBSome in the cytoplasm.
    action: ACCEPT
    reason: >-
      Strongly supported by PMID:22072986 (cytoplasmic localization) and UniProt subcellular
      location (Cytoplasm).
    supported_by:
    - reference_id: PMID:22072986
      supporting_text: >-
        LZTFL1 was detected throughout the cytoplasm
- term:
    id: GO:1903565
    label: negative regulation of protein localization to cilium
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic inference of the core function: LZTFL1 negatively regulates localization of
      the BBSome (and its cargo) to the cilium. Captures the central biological role and is
      corroborated by direct experimental (IMP) evidence in human cells. Falcon deep research adds
      a mechanistic link: LZTFL1 physically interacts with IFT27 (an IFT-B subunit), connecting
      it to the IFT-B/BBSome axis that controls BBSome ciliary entry/export (Huang 2021).
    action: ACCEPT
    reason: >-
      Core function. Supported by IBA and by IMP (PMID:22072986): LZTFL1 depletion increases,
      and overexpression decreases, BBSome ciliary localization. The LZTFL1-IFT27 interaction
      summarized in the falcon deep research provides a candidate molecular coupling to the IFT
      machinery (note: GPCR-export and Hedgehog effects are largely whole-pathway behaviors of
      the IFT27/BBSome axis rather than demonstrated LZTFL1-protein activities, so they are not
      annotated to LZTFL1 here).
    supported_by:
    - reference_id: PMID:22072986
      supporting_text: >-
        LZTFL1 is a specific regulator of BBSome ciliary trafficking but not general IFT
    - reference_id: file:human/LZTFL1/LZTFL1-deep-research-falcon.md
      supporting_text: >-
        LZTFL1 physically interacts with IFT27, a component of the IFT-B complex, as demonstrated
        by yeast two-hybrid screening, co-immunoprecipitation, colocalization studies, and
        luciferase complementation assays
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: >-
      Electronic (IEA) cytoplasm localization, consistent with the IBA and experimental cytosol
      annotations.
    action: ACCEPT
    reason: Consistent with experimentally established cytoplasmic localization (PMID:22072986).
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:22072986
  qualifier: enables
  review:
    summary: >-
      Generic protein binding (IPI) from interaction with BBS9 (Q3SYG4). The underlying
      interaction is real and biologically central, but the bare "protein binding" term is
      uninformative; the BBSome-binding activity is better captured by protein-containing complex
      binding.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Per curation guidelines, avoid uninformative "protein binding". The BBS9/BBSome interaction
      is better represented by GO:0044877 (protein-containing complex binding), already annotated.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: >-
      Generic protein binding from a large-scale interactome screen (partners include SDCBP).
      Uninformative term.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative "protein binding"; high-throughput interactome data without specific functional meaning.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:27173435
  qualifier: enables
  review:
    summary: Generic protein binding (interaction with BBS9, Q3SYG4) from an organelle proteome map. Uninformative term.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative "protein binding"; better captured by protein-containing complex binding for the BBSome.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  qualifier: enables
  review:
    summary: Generic protein binding (BBS9, Q3SYG4) from a large-scale interactome study. Uninformative term.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative "protein binding"; high-throughput interactome data.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31515488
  qualifier: enables
  review:
    summary: Generic protein binding (NTAQ1, Q96HA8) from a population variant interactome study. Uninformative term.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative "protein binding"; high-throughput interactome data.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: >-
      Generic protein binding from the HuRI reference binary interactome (partners include
      proteasome subunits PSMA1/PSMB1, MOB1A, PELI2, PICK1, TRIM68, EHHADH). Uninformative term.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative "protein binding"; high-throughput binary interactome data.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: Generic protein binding (BBS9, Q3SYG4) from the BioPlex interactome. Uninformative term.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative "protein binding"; high-throughput interactome data.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:22072986
  qualifier: enables
  review:
    summary: >-
      Self/identical protein binding (Q9NQ48 with Q9NQ48). Strongly supported by directed
      experiments showing LZTFL1 forms homo-oligomers (co-purification of endogenous LZTFL1,
      co-IP, and in vitro crosslinking).
    action: ACCEPT
    reason: >-
      PMID:22072986 demonstrates homo-oligomerization. Informative, experimentally grounded
      self-association activity.
    supported_by:
    - reference_id: PMID:22072986
      supporting_text: >-
        indicating that LZTFL1 forms homo-oligomers
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: Self-binding (Q9NQ48 homodimer) from a large-scale interactome screen, corroborating the experimentally established homo-oligomerization.
    action: ACCEPT
    reason: Consistent with directed homo-oligomerization data (PMID:22072986).
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:27107012
  qualifier: enables
  review:
    summary: Self-binding (Q9NQ48 homodimer) from a barcode-fusion-genetics interaction screen, corroborating homo-oligomerization.
    action: ACCEPT
    reason: Consistent with directed homo-oligomerization data (PMID:22072986).
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: Self-binding (Q9NQ48 homodimer) from the HuRI reference binary interactome, corroborating homo-oligomerization.
    action: ACCEPT
    reason: Consistent with directed homo-oligomerization data (PMID:22072986).
- term:
    id: GO:0002177
    label: manchette
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Electronic, mouse-orthology-based (ECO:0000265, from mouse Q9JHQ5) localization to the
      manchette, the transient spermatid microtubule structure. Plausible given strong testis
      expression and reported sperm-body localization of the rodent ortholog, but supported only
      by automated orthology transfer for the human protein. Falcon deep research corroborates
      the orthologous source observation: during mouse spermiogenesis the protein localizes to
      the developing flagellum and near the manchette at the elongated spermatid stage.
    action: KEEP_AS_NON_CORE
    reason: >-
      Tissue/stage-specific localization inferred from the mouse ortholog; consistent with testis
      expression but not the core function and not directly demonstrated for human LZTFL1. The
      manchette-proximal localization is reported for the rodent ortholog (Huang 2021, summarized
      in the falcon deep research); kept non-core pending direct human evidence.
    supported_by:
    - reference_id: file:human/LZTFL1/LZTFL1-deep-research-falcon.md
      supporting_text: >-
        LZTFL1 localizes to the developing flagellum and appears near the manchette, a transient
        microtubule structure involved in sperm head shaping
- term:
    id: GO:0005929
    label: cilium
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Electronic, mouse-orthology-based localization to cilium. As with the IBA cilium
      annotation, the primary human study found LZTFL1 is cytoplasmic and NOT enriched in cilia.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Contradicted for the human protein by direct evidence of cytoplasmic, non-ciliary
      localization (PMID:22072986). Orthology transfer overstates ciliary residence.
- term:
    id: GO:0044877
    label: protein-containing complex binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: enables
  review:
    summary: >-
      Electronic, mouse-orthology-based protein-containing complex binding, capturing the
      BBSome-binding activity. Well aligned with the experimentally established LZTFL1-BBSome
      interaction.
    action: ACCEPT
    reason: >-
      Captures the biologically central BBSome-binding activity; corroborated by IDA
      (PMID:24550735) and the BBS9/BBSome co-purification in PMID:22072986.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: >-
      Direct immunofluorescence (HPA) localization to cytosol, consistent with the experimentally
      established cytoplasmic distribution of LZTFL1.
    action: ACCEPT
    reason: Supported by HPA IDA and by PMID:22072986 (cytoplasmic localization).
- term:
    id: GO:1903565
    label: negative regulation of protein localization to cilium
  evidence_type: IMP
  original_reference_id: PMID:22072986
  qualifier: involved_in
  review:
    summary: >-
      Direct mutant-phenotype evidence for the core function: LZTFL1 negatively regulates BBSome
      (BBS9/BBS4/BBS8) localization to the cilium. LZTFL1 depletion increases, and overexpression
      decreases, ciliary BBSome; effect is specific to the BBSome and not general IFT.
    action: ACCEPT
    reason: >-
      Core function, directly demonstrated by loss/gain-of-function in PMID:22072986.
    supported_by:
    - reference_id: PMID:22072986
      supporting_text: >-
        over-expression of wild-type LZTFL1 inhibited ciliary localization of BBS9
- term:
    id: GO:1903568
    label: negative regulation of protein localization to ciliary membrane
  evidence_type: IMP
  original_reference_id: PMID:22072986
  qualifier: involved_in
  review:
    summary: >-
      Direct mutant-phenotype evidence that LZTFL1 negatively regulates trafficking of membrane
      cargo (e.g. Smoothened) to the ciliary membrane via control of the BBSome. More specific
      sibling of the cilium term and captures the SMO/ciliary-membrane aspect.
    action: ACCEPT
    reason: >-
      Supported by PMID:22072986: LZTFL1 suppresses SMO ciliary (membrane) localization. Core
      function.
    supported_by:
    - reference_id: PMID:22072986
      supporting_text: >-
        LZTFL1 suppresses SMO localization to cilia
- term:
    id: GO:0044877
    label: protein-containing complex binding
  evidence_type: IDA
  original_reference_id: PMID:24550735
  qualifier: enables
  review:
    summary: >-
      Direct experimental evidence for binding a protein-containing complex (the BBSome).
      Although this paper's title/abstract concern AZI1/CEP131, LZTFL1 was assayed as a
      BBSome-associated protein; the curator (UniProt) read the full text. This captures the
      central BBSome-binding activity of LZTFL1.
    action: ACCEPT
    reason: >-
      Informative molecular function representing the experimentally established LZTFL1-BBSome
      (via BBS9) interaction; do not overrule an IDA on the basis of the abstract focus.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-5624129
  qualifier: located_in
  review:
    summary: >-
      Traceable-author (Reactome) cytosol localization, consistent with the experimentally
      established cytoplasmic/cytosolic distribution of LZTFL1.
    action: ACCEPT
    reason: Consistent with HPA IDA cytosol and PMID:22072986 cytoplasmic localization.
core_functions:
- description: >-
    Negative regulator of BBSome ciliary trafficking: LZTFL1 binds the BBSome in the cytoplasm
    and restrains its entry into (or promotes its retrieval from) the cilium, thereby controlling
    BBSome ciliary localization.
  supported_by:
  - reference_id: PMID:22072986
    supporting_text: >-
      over-expression of wild-type LZTFL1 inhibited ciliary localization of BBS9
  - reference_id: PMID:22072986
    supporting_text: >-
      LZTFL1 is a specific regulator of BBSome ciliary trafficking but not general IFT
  molecular_function:
    id: GO:0044877
    label: protein-containing complex binding
  directly_involved_in:
  - id: GO:1903565
    label: negative regulation of protein localization to cilium
- description: >-
    Regulation of ciliary trafficking of the Hedgehog transducer Smoothened (and hence Sonic
    hedgehog pathway responsiveness) through control of the BBSome, restraining SMO localization
    to the ciliary membrane.
  supported_by:
  - reference_id: PMID:22072986
    supporting_text: >-
      LZTFL1 suppresses SMO localization to cilia
  directly_involved_in:
  - id: GO:1903568
    label: negative regulation of protein localization to ciliary membrane
- description: >-
    Self-association into homo-oligomers, which is part of how LZTFL1 assembles to engage the
    BBSome (via the subunit BBS9).
  supported_by:
  - reference_id: PMID:22072986
    supporting_text: >-
      indicating that LZTFL1 forms homo-oligomers
  molecular_function:
    id: GO:0042802
    label: identical protein binding
proposed_new_terms: []
suggested_questions:
- question: >-
    Does LZTFL1 act primarily by blocking BBSome ciliary entry, by promoting BBSome ciliary exit
    (retrieval), or both, and what is the molecular trigger that releases this inhibition?
- question: >-
    Is the rodent manchette / sperm-flagellum localization of LZTFL1 conserved in humans, and does
    LZTFL1 have a BBSome-independent role in spermatogenesis relevant to its testis enrichment?
- question: >-
    Are the high-throughput interactions with non-BBSome partners (e.g. SDCBP/syntenin, proteasome
    subunits, MOB1A, PICK1) biologically meaningful for LZTFL1 function or trafficking turnover?
- question: >-
    Does LZTFL1 have a BBSome-independent clathrin-adaptor role? A primary study (Promchan & Natarajan
    2020, PLoS ONE e0226298, summarized in the falcon deep research) reports direct LZTFL1 binding to
    AP-1 (beta1) and AP-2 (beta2) via a conserved DxxFxxLxxxR motif and selective regulation of
    transferrin receptor (TfR1) surface levels/endocytosis. If confirmed and curated, this would
    warrant clathrin-adaptor / AP-complex-binding molecular-function and TGN/endosomal-trafficking
    process annotations distinct from the BBSome ciliary role (not yet in GOA; primary paper not in
    the cache, so not annotated here).
suggested_experiments:
- description: >-
    Live-cell imaging of tagged BBSome subunits with acute LZTFL1 degradation (e.g. auxin-inducible
    degron) to distinguish whether LZTFL1 controls ciliary entry vs. retrieval/exit kinetics.
- description: >-
    Structural/biochemical mapping of the LZTFL1 N-terminal regulatory region (including the
    conserved K24/R25 basic motif whose mutation is dominant-negative) to identify the effector
    that links BBSome binding to inhibition of ciliary entry.
- description: >-
    Generate LZTFL1-null vs. BBS17 patient-variant (e.g. L87P) knock-in cells/organoids and quantify
    BBSome and SMO ciliary dynamics plus SHH target-gene output to relate molecular defect to disease.
references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  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:22072986
  title: A novel protein LZTFL1 regulates ciliary trafficking of the BBSome and Smoothened.
  findings:
  - statement: >-
      LZTFL1 is a cytoplasmic protein (not enriched in cilia/basal body) that binds the BBSome
      via BBS9, self-associates into homo-oligomers, and negatively regulates BBSome and
      Smoothened ciliary trafficking; it acts specifically on the BBSome, not general IFT.
    reference_section_type: RESULTS
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Full text available and read; foundational functional paper establishing LZTFL1 as a
      cytoplasmic negative regulator of BBSome/SMO ciliary trafficking and as a BBS9-binding
      homo-oligomer. Directly supports the core annotations.
- id: PMID:24550735
  title: The centriolar satellite protein AZI1 interacts with BBS4 and regulates ciliary
    trafficking of the BBSome.
  findings:
  - statement: >-
      Study of AZI1/CEP131 as a BBSome-trafficking regulator in which LZTFL1 was assayed as a
      BBSome-associated protein, supporting the IDA protein-containing complex binding annotation.
    reference_section_type: RESULTS
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Abstract only in cache (full text unavailable); title/abstract concern AZI1/CEP131 but the
      UniProt-assigned IDA on LZTFL1 (GO:0044877) reflects LZTFL1 assayed as a BBSome-associated
      protein. Defer to curator; do not remove on incomplete evidence.
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome (Rolland et al.); supports self-binding and generic protein-binding annotations.
- id: PMID:27107012
  title: Pooled-matrix protein interaction screens using Barcode Fusion Genetics.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interaction screen; supports LZTFL1 self-binding (identical protein binding).
- id: PMID:27173435
  title: An organelle-specific protein landscape identifies novel diseases and molecular
    mechanisms.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Organelle proteome map; source of a generic protein-binding (BBS9) annotation.
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome; source of a generic protein-binding (BBS9) annotation.
- id: PMID:31515488
  title: Extensive disruption of protein interactions by genetic variants across the
    allele frequency spectrum in human populations.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Variant interactome study; source of a generic protein-binding (NTAQ1) annotation.
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: HuRI reference binary interactome; supports self-binding and multiple generic protein-binding annotations.
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: BioPlex interactome; source of a generic protein-binding (BBS9) annotation.
- id: Reactome:R-HSA-5624129
  title: LZTFL1 binds the BBSome and prevents its traffic to the cilium
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Reactome reaction matching the established mechanism (LZTFL1 binds BBSome and prevents
      ciliary trafficking); supports the cytosol localization and BBSome-binding annotations.
- id: file:human/LZTFL1/LZTFL1-deep-research-falcon.md
  title: Falcon deep research report for LZTFL1
  findings:
  - statement: >-
      LZTFL1-specific findings: physical interaction with IFT27 (yeast two-hybrid, co-IP,
      colocalization, luciferase complementation; Huang 2021); direct binding to AP-1 (beta1)
      and AP-2 (beta2) via a conserved DxxFxxLxxxR motif with participation in TfR1 trafficking
      (Promchan 2020); and stage-specific testis localization to the developing flagellum and
      near the manchette during spermiogenesis (Huang 2021).
    reference_section_type: RESULTS
  reference_review:
    relevance: MEDIUM
    correctness: UNVERIFIED
    review_notes: >-
      LLM-generated synthesis (Edison/Falcon); citations not independently re-verified, so kept
      UNVERIFIED. LZTFL1-SPECIFIC, well-anchored claims usable for this review: (1) direct
      IFT27 interaction and a role linking the BBSome to the IFT-B machinery (Huang 2021,
      ydbio 2021); (2) direct AP-1/AP-2 binding via a DxxFxxLxxxR motif and selective effect on
      transferrin receptor (TfR1) cell-surface levels/endocytosis, an LZTFL1-specific clathrin-
      adaptor trafficking role distinct from the BBSome (Promchan 2020, PLoS ONE e0226298);
      (3) testis/spermatid localization to developing flagellum and manchette region (Huang
      2021), corroborating the orthology-based manchette and sperm-motility annotations.
      CAUTIONS: the report states LZTFL1 "also localizes to primary cilia" and attributes
      BBSome/IFT-B/Hedgehog/GPCR-export functions broadly — much of that is whole-BBSome/IFT
      pathway behavior inferred onto LZTFL1, and the ciliary-localization claim CONTRADICTS the
      primary functional study (PMID:22072986: LZTFL1 is cytoplasmic and NOT enriched in cilia),
      so it is NOT used to support ciliary residence here. The COVID-19 3p21.31 association is a
      REGULATORY-LOCUS / eQTL effect (rs17713054 enhancer altering LZTFL1 expression in lung
      epithelium) and an EMT phenotype, NOT a demonstrated molecular function of the LZTFL1
      protein; it is excluded from molecular-function/process annotations.

Category	Finding	Details	Key experimental evidence	Citations
Primary molecular function/activity	Trafficking adaptor/regulator, not an enzyme	LZTFL1 functions as a regulatory trafficking protein rather than a catalyst; current evidence supports roles in ciliary/BBSome trafficking and clathrin adaptor-mediated membrane trafficking	Reviews place LZTFL1/BBS17 among BBSome regulators; primary studies show direct protein-protein interactions and trafficking phenotypes rather than enzymatic activity (wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2, promchan2020leucinezippertranscription pages 7-9)	(wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2, promchan2020leucinezippertranscription pages 7-9)
Primary molecular function/activity	Negative regulator of BBSome ciliary entry / regulator of BBSome export dynamics	LZTFL1 regulates BBSome behavior in cilia and is required for proper coupling of BBSome-dependent export with IFT machinery	Reviews summarize that LZTFL1 loss causes BBSome accumulation in cilia; RABL2(Q80L) or IFT27 defects phenocopy abnormal ciliary accumulation of LZTFL1/BBSome and impaired GPCR export (wingfield2018traffickingofciliary pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5)	(wingfield2018traffickingofciliary pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5)
Primary molecular function/activity	Accessory factor for AP-1/AP-2-mediated trafficking	LZTFL1 directly binds adaptor complexes AP-1 and AP-2 and helps regulate specific cargo trafficking, especially transferrin receptor 1 (TfR1)	In vitro pull-down and co-immunoprecipitation showed direct binding to AP-1/AP-2 and functional effects on TfR1 surface levels and endocytosis (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9, promchan2020leucinezippertranscription pages 14-17)	(promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9, promchan2020leucinezippertranscription pages 14-17)
Direct binding partners	IFT27	LZTFL1 physically associates with IFT27, linking it functionally to the IFT-B/BBSome axis	Identified by yeast two-hybrid; confirmed by co-immunoprecipitation, colocalization, and luciferase complementation assays (huang2021leucinezippertranscription pages 7-11, huang2021leucinezippertranscription pages 11-15)	(huang2021leucinezippertranscription pages 7-11, huang2021leucinezippertranscription pages 11-15)
Direct binding partners	AP-1 β1 subunit	Direct binding to AP-1 β1 supports a role in AP-1-dependent membrane trafficking	Purified-protein pull-down assays demonstrated direct interaction with AP-1 β1 but not all AP-1 subunits (promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9)	(promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9)
Direct binding partners	AP-2 β2 subunit	Direct binding to AP-2 β2 suggests participation in endocytic adaptor pathways	Purified-protein pull-down assays showed direct interaction dependent on an AP-binding motif in LZTFL1 (promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9)	(promchan2020leucinezippertranscription pages 2-4, promchan2020leucinezippertranscription pages 7-9)
Direct binding partners	TfR1 is an indirect partner/cargo-associated protein	LZTFL1 co-immunoprecipitates with TfR1, but available evidence indicates the interaction is indirect, likely via AP-1/AP-2 complexes	Co-IP detected association, whereas purified-protein assays did not show direct LZTFL1-TfR1 binding; DxxFxxLxxxR motif was required for the association in cells (promchan2020leucinezippertranscription pages 14-17, promchan2020leucinezippertranscription pages 11-14)	(promchan2020leucinezippertranscription pages 14-17, promchan2020leucinezippertranscription pages 11-14)
Subcellular localization	Cytoplasm	LZTFL1 is predominantly cytoplasmic in transfected cells and endogenous contexts	CHO-cell localization showed cytoplasmic LZTFL1; review/primary literature describe it as a cytoplasmic and ciliary protein (promchan2020leucinezippertranscription pages 1-2, huang2021leucinezippertranscription pages 11-15)	(promchan2020leucinezippertranscription pages 1-2, huang2021leucinezippertranscription pages 11-15)
Subcellular localization	Perinuclear region / trans-Golgi network-associated compartment	LZTFL1 colocalizes with AP-1 in the perinuclear region encompassing TGN and peripheral endosomal compartments	Immunofluorescence, BFA washout, and AP-1 knockdown experiments showed Arf-dependent PNR localization and AP-1 dependence of PNR accumulation (promchan2020leucinezippertranscription pages 11-14)	(promchan2020leucinezippertranscription pages 11-14)
Subcellular localization	Primary cilium	LZTFL1 localizes to cilia and participates in ciliary protein trafficking and signaling organization	Cilia-focused reviews and IFT/BBSome studies place LZTFL1 within the ciliary trafficking system; ciliary accumulation occurs in trafficking-defective states (wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5)	(wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5)
Subcellular localization	Spermatid cytoplasm, developing flagellum, and manchette-proximal region	In germ cells, LZTFL1 shows a vesicular cytoplasmic pattern in round spermatids and later localizes to developing flagella and near the manchette	Testis immunofluorescence during spermiogenesis documented stage-specific localization (huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 11-15)	(huang2021leucinezippertranscription pages 1-7, huang2021leucinezippertranscription pages 11-15)
Major biological pathways	Intraflagellar transport/BBSome pathway	LZTFL1 acts in the IFT-B/BBSome system that controls ciliary membrane protein trafficking, especially export/removal of selected cargos from cilia	Reviews and mechanistic studies connect LZTFL1 with IFT27/IFT25 and BBSome trafficking; defects cause BBSome/LZTFL1 accumulation and GPCR export failure (wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2)	(wingfield2018traffickingofciliary pages 1-2, nakayama2018ciliaryproteintrafficking pages 1-2, zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2)
Major biological pathways	Hedgehog signaling	Through its role in ciliary trafficking, LZTFL1 is linked to Hedgehog pathway organization, including trafficking of Smoothened/GPR161-related machinery and tip localization of signaling proteins	IFT27/BBSome pathway studies show defects in ciliary trafficking of Smo/GPR161 and Gli/Kif7/SuFu localization when this axis is perturbed (zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5)	(zhou2022cep19–rabl2–iftbaxiscontrols pages 1-2, eguether2018intraflagellartransportis pages 1-5)
Major biological pathways	Clathrin-mediated endocytosis and recycling	LZTFL1 contributes to AP-1/AP-2-dependent trafficking of TfR1, affecting transferrin uptake, efflux, and internalization	LZTFL1 knockout reduced TfR1 surface abundance and endocytosis/internalization kinetics without broadly affecting all AP-1 cargos tested (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 14-17, promchan2020leucinezippertranscription pages 11-14)	(promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 14-17, promchan2020leucinezippertranscription pages 11-14)
Major biological pathways	Epithelial-mesenchymal transition (EMT) / epithelial differentiation	LZTFL1 is implicated as an EMT-suppressive factor in epithelial cells and cancer contexts; increased LZTFL1 expression is linked to reduced EMT, while suppression promotes invasion/metastasis	COVID-19 risk-locus work highlighted LZTFL1 as an EMT-regulating effector in pulmonary epithelium; breast-cancer study identified LZTFL1 as a miR-21 target whose loss promotes EMT and metastasis (downes2021identificationoflztfl1 pages 1-2, wang2019microrna21promotesbreast pages 1-2, downes2021identificationoflztfl1 pages 3-4)	(downes2021identificationoflztfl1 pages 1-2, wang2019microrna21promotesbreast pages 1-2, downes2021identificationoflztfl1 pages 3-4)
Major biological pathways	Immune synapse formation	Earlier work cited in primary trafficking study places LZTFL1 in immune synapse biology in activated T cells	Introductory synthesis in the AP-1/AP-2 paper cites immune synapse participation as an established function (promchan2020leucinezippertranscription pages 1-2)	(promchan2020leucinezippertranscription pages 1-2)
Key experimental evidence	Motif/domain requirement for adaptor binding	The DxxFxxLxxxR motif is essential for AP-1/AP-2 binding and for indirect association with TfR1	Mutagenesis in cell-based and in vitro assays abolished AP-1/AP-2 interaction and disrupted TfR1-associated behavior (promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 7-9, promchan2020leucinezippertranscription pages 14-17)	(promchan2020leucinezippertranscription pages 1-2, promchan2020leucinezippertranscription pages 7-9, promchan2020leucinezippertranscription pages 14-17)
Key experimental evidence	Trafficking specificity for TfR1	LZTFL1 loss reduced TfR1 cell-surface abundance by roughly 40-50%, but did not similarly alter EGFR or CI-MPR in the same assay system	Surface biotinylation and uptake/internalization assays in WT versus LZTFL1-knockout HeLa cells (promchan2020leucinezippertranscription pages 14-17)	(promchan2020leucinezippertranscription pages 14-17)
Key experimental evidence	Reproductive/ciliopathy phenotype in vivo	Lztfl1 deficiency causes reduced male fertility, low sperm motility, abnormal sperm morphology, and is linked to BBS phenotypes such as obesity and retinal degeneration	Knockout mouse analyses plus human BBS genetics support a physiological role in cilia/flagella biology (huang2021leucinezippertranscription pages 1-7, melluso2023bardetbiedlsyndromecurrent pages 6-8, huang2021leucinezippertranscription pages 7-11)	(huang2021leucinezippertranscription pages 1-7, melluso2023bardetbiedlsyndromecurrent pages 6-8, huang2021leucinezippertranscription pages 7-11)
Key experimental evidence	Human disease genetics and recent clinical relevance	Homozygous loss-of-function variants cause Bardet-Biedl syndrome (BBS17/LZTFL1); regulatory upregulation of LZTFL1 at 3p21.31 is implicated in severe COVID-19 risk in pulmonary epithelial cells	Recent consensus/review literature recognizes BBS17/LZTFL1; multi-omics fine-mapping identified LZTFL1 as the likely effector gene at the COVID-19 risk locus (downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4, melluso2023bardetbiedlsyndromecurrent pages 6-8)	(downes2021identificationoflztfl1 pages 1-2, downes2021identificationoflztfl1 pages 3-4, melluso2023bardetbiedlsyndromecurrent pages 6-8)

LZTFL1

Gene Description

Existing Annotations Review

Core Functions

Negative regulator of BBSome ciliary trafficking: LZTFL1 binds the BBSome in the cytoplasm and restrains its entry into (or promotes its retrieval from) the cilium, thereby controlling BBSome ciliary localization.

Regulation of ciliary trafficking of the Hedgehog transducer Smoothened (and hence Sonic hedgehog pathway responsiveness) through control of the BBSome, restraining SMO localization to the ciliary membrane.

Self-association into homo-oligomers, which is part of how LZTFL1 assembles to engage the BBSome (via the subunit BBS9).

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Comprehensive Research Report: LZTFL1 (Leucine Zipper Transcription Factor-Like Protein 1)

Gene Identity and Overview

Primary Molecular Function

Ciliary BBSome Regulation

Clathrin Adaptor-Mediated Trafficking

Subcellular Localization

Biological Pathways and Signaling Networks

Intraflagellar Transport and Ciliogenesis

Hedgehog Signaling Pathway

Epithelial-Mesenchymal Transition and Cancer

Other Biological Roles

Structural Features and Functional Domains

Disease Associations

Summary

Artifacts

Citations

📚 Additional Documentation

Notes

LZTFL1 (BBS17) — Gene Review Notes

Summary of function

Key evidence

PMID:22072986 (Seo et al. 2011, PLoS Genet) — the foundational functional paper (full text available)

PMID:22510444 (Marion et al. 2012, J Med Genet) — disease/BBS17 (abstract/UniProt only)

PMID:23692385 (Schaefer et al. 2014) — mesoaxial polydactyly major feature in BBS17; variant L87P.

PMID:24550735 (Chamling et al. 2014, PLoS Genet) — AZI1/CEP131 paper (abstract only; full_text_available: false)

Protein-interaction (IPI) annotations

Localization

Tumor-suppressor / other (NOT in GOA being reviewed)

Core function synthesis

📄 View Raw YAML