Affinage

IFT74

Intraflagellar transport protein 74 homolog · UniProt Q96LB3

Length
600 aa
Mass
69.2 kDa
Annotated
2026-04-28
22 papers in source corpus 9 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

IFT74 is a core subunit of the intraflagellar transport complex B (IFT-B) that is essential for cilium assembly, maintenance, and cargo trafficking. It heterodimerizes with IFT81 via coiled-coil domains to form a tetrameric (IFT81)₂(IFT74)₂ scaffold that nucleates IFT-B core assembly; the IFT74–IFT81 coiled-coil additionally acts as an unconventional GTPase-activating protein (GAP) for RabL2, controlling IFT train initiation at the ciliary base (PMID:15955805, PMID:37606072). Distinct IFT74 domains serve separable functions: the N-terminal basic region (aa 1–130) binds tubulin and is preferentially required for motile cilia that have high tubulin transport demands, an internal coiled-coil segment (aa 131–196) mediates IFT-A/IFT-B association at the ciliary base, and the C-terminal region binds the IFT25–IFT27 dimer to coordinate BBSome-dependent export of ciliary membrane proteins (PMID:26051893, PMID:37315079, PMID:34888642). Loss-of-function and hypomorphic variants in IFT74 cause a spectrum of ciliopathies including Joubert syndrome, Bardet–Biedl syndrome, skeletal ciliopathy with motile cilia dysfunction, and isolated male infertility with sperm flagellar defects (PMID:33531668, PMID:34888642, PMID:33689014).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2005 High

    Establishing IFT74 as a core IFT-B scaffold subunit resolved how the ~500-kDa IFT-B core is organized and showed that IFT74 and IFT81 form the central oligomeric backbone.

    Evidence High-ionic-strength fractionation, chemical cross-linking, and yeast two-/three-hybrid assays using Chlamydomonas and vertebrate IFT-B subunits

    PMID:15955805

    Open questions at the time
    • The functional significance of IFT74 domains beyond the coiled-coil was unknown
    • No in vivo loss-of-function data for IFT74 at this stage
    • Cargo-binding activities of the IFT74–IFT81 dimer were uncharacterized
  2. 2015 High

    Domain-resolution rescue mapping of IFT74 in a null mutant separated three functional regions: aa 197–641 for IFT-B stabilization, aa 131–196 for IFT-A/IFT-B coupling at the ciliary base, and aa 1–130 for tubulin import into flagella.

    Evidence Chlamydomonas ift74-null rescue with serial truncation constructs and fluorescence imaging of IFT train dynamics

    PMID:26051893

    Open questions at the time
    • Whether tubulin binding by the N-terminus is direct or requires co-factors was not resolved
    • The mechanism linking the 131–196 region to IFT-A association was unclear
  3. 2021 Medium

    Identification of IFT74 variants in Joubert syndrome patients, combined with ciliogenesis and Hedgehog signaling defects in patient fibroblasts, established IFT74 as a Joubert syndrome gene and connected its loss to ciliary membrane protein mislocalization.

    Evidence Zebrafish ift74 morphant rescue with patient variant p.Q179E, patient fibroblast ciliary assays, and immunofluorescence for ARL13B/INPP5E/GPR161

    PMID:33531668

    Open questions at the time
    • Only a single missense variant tested in zebrafish rescue
    • Precise structural basis for how Q179E disrupts IFT-B integrity was not determined
  4. 2021 Medium

    Zebrafish ift74 mutants revealed that IFT74 is required not just for ciliogenesis but also for cilium maintenance, as photoreceptor connecting cilia formed but progressively degenerated with slow opsin transport—distinguishing IFT74 from other IFT-B subunits.

    Evidence Zebrafish ift74 mutant analysis with opsin immunofluorescence and live cilia imaging

    PMID:34502236

    Open questions at the time
    • Mechanism underlying the milder phenotype compared with other IFT-B subunit mutants was not explained
    • Whether this reflects partial redundancy with IFT81 or cargo selectivity was untested
  5. 2021 Medium

    Discovery of an IFT74 missense variant affecting splicing and flagellar localization in infertile males extended the disease spectrum to non-syndromic male infertility (MMAF), implicating IFT74 in sperm flagellum biogenesis.

    Evidence Exome sequencing, RT-PCR splicing analysis, immunofluorescence in patient sperm

    PMID:33689014

    Open questions at the time
    • Single family study; independent replication in additional MMAF cohorts not reported
    • Quantitative impact on IFT-B assembly was not assessed biochemically
  6. 2022 High

    Mapping the IFT25–IFT27 binding site to the IFT74–IFT81 C-terminal region, and showing that BBS-causing variants in IFT74 or IFT27 disrupt this interaction, provided a molecular mechanism linking the IFT-B core to BBSome-dependent ciliary membrane protein export.

    Evidence Co-immunoprecipitation, IFT74-KO and IFT27-KO cell rescue, ciliary BBSome export assays

    PMID:34888642

    Open questions at the time
    • Structural details of the IFT74–IFT25/27 interface were not resolved
    • Whether all BBS-associated ciliary cargo is equally affected was not tested
  7. 2023 High

    Demonstrating that the IFT81–IFT74 coiled-coil acts as a GAP for RabL2 provided a mechanistic explanation for how IFT trains are released from the ciliary base after assembly, linking IFT-B core architecture to train initiation control.

    Evidence In vitro reconstituted pentameric IFT complex GTPase assay, 70-aa coiled-coil domain mapping, cross-species validation

    PMID:37606072

    Open questions at the time
    • In vivo validation of GAP-dead IFT74/81 mutants on IFT train dynamics is lacking
    • Structural basis of the unconventional GAP mechanism is unresolved
  8. 2023 High

    Mouse knock-in and patient studies of an IFT74 exon-2 deletion (Δaa 1–40) showed that the extreme N-terminal tubulin-binding segment is selectively required for motile cilia function over primary cilia, explaining tissue-selective ciliopathy phenotypes.

    Evidence Mouse knock-in models, patient nasal epithelial cells, in vitro tubulin binding, AP-MS of truncated IFT74, electron microscopy

    PMID:37315079 PMID:37555648

    Open questions at the time
    • How tubulin binding by 40 aa is mechanistically coupled to axonemal assembly remains unclear
    • Whether other tubulin-binding IFT subunits partially compensate in primary cilia is untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • No high-resolution structure of the full-length IFT74–IFT81 heterodimer or its interfaces with IFT25–IFT27 and RabL2 exists, and the in vivo consequences of selectively ablating the GAP activity versus tubulin binding versus IFT25/27 binding have not been dissected in a single genetic system.
  • Full-length atomic structure of IFT74–IFT81 is unavailable
  • Separation-of-function alleles addressing GAP vs. tubulin vs. IFT25/27 binding in one model organism are needed
  • Whether IFT74 has additional non-ciliary functions has not been addressed

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 2 GO:0098772 molecular function regulator activity 1
Localization
GO:0005929 cilium 4 GO:0005829 cytosol 2
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 5 R-HSA-5653656 Vesicle-mediated transport 2
Partners
IFT25IFT27IFT46IFT52IFT81IFT88RABL2
Complex memberships
IFT-B complexIFT74-IFT81 heterotetramer

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 IFT74/72 and IFT81 directly interact to form a higher-order oligomer (tetrameric complex (IFT81)2(IFT74/72)2) that serves as a scaffold for IFT complex B assembly; IFT complex B has a 500-kDa core containing IFT88, IFT81, IFT74/72, IFT52, IFT46, and IFT27, with IFT172, IFT80, IFT57, and IFT20 as peripheral subunits. High-ionic-strength fractionation of Chlamydomonas IFT complex B, chemical cross-linking, yeast two-hybrid and three-hybrid analyses, conservation confirmed with vertebrate homologues The Journal of biological chemistry High 15955805
2015 IFT74 is required to stabilize IFT-B complex in vivo; aa 197-641 are sufficient for IFT-B stabilization. The N-terminal charged region (aa 1-130) contributes to but is not strictly required for tubulin entry into flagella, whereas aa 131-196 (part of coiled-coil 1) are required for IFT-A/IFT-B association at the ciliary base and for flagellar import of IFT-A. Chlamydomonas ift74 null mutant rescue experiments with truncated IFT74 constructs, fluorescence microscopy of IFT train assembly and movement Current biology : CB High 26051893
2022 The IFT25-IFT27 dimer binds the C-terminal region of the IFT74-IFT81 dimer; Bardet-Biedl syndrome (BBS) variants of IFT74 delete this IFT25-IFT27-binding region, and BBS variants of IFT27 are impaired in IFT74-IFT81 binding, demonstrating that impaired IFT74-IFT81/IFT25-IFT27 interaction causes BBS-associated ciliary defects. Co-immunoprecipitation, IFT74-knockout and IFT27-knockout cell rescue assays, ciliary phenotype analysis (BBSome export defects) Human molecular genetics High 34888642
2023 The IFT81-IFT74 complex acts as an unconventional GAP for the small GTPase RabL2: a reconstituted pentameric IFT complex containing IFT81/74 enhances RabL2 GTP hydrolysis, with the activity mapped to a 70-aa coiled-coil region of IFT81/74. This provides a molecular mechanism for RabL2 dissociation from anterograde IFT trains after departure from the ciliary base. In vitro reconstitution and purification of RabL2-IFT complexes, GTPase activity assays, structural modeling validated in vitro and in cellulo, Chlamydomonas IFT81/74 tested with human RabL2 The EMBO journal High 37606072
2023 The first 40 amino acids of IFT74 (encoded by exon 2) are dispensable for binding to other IFT-B subunits but are important for tubulin binding; deletion of these residues preferentially impairs motile cilia function (mucociliary clearance) over primary cilia assembly, consistent with higher tubulin transport demands in motile cilia. In vitro binding assays with truncated IFT74, mouse knock-in alleles (exon 2 deletion and null), human patient fibroblast/cell analysis, electron microscopy of cilia PLoS genetics High 37315079
2021 IFT74 variants cause Joubert syndrome; patient-derived fibroblasts with IFT74 variants show attenuated ciliogenesis, altered distribution of IFT proteins, mislocalisation of ciliary membrane proteins ARL13B, INPP5E, and GPR161, and disrupted hedgehog signaling. Zebrafish ift74 morphant rescue with human variant IFT74 (p.Q179E), patient fibroblast ciliogenesis assays, immunofluorescence for ciliary protein distribution, hedgehog signaling assays Genetics in medicine : official journal of the American College of Medical Genetics Medium 33531668
2021 A missense variant in IFT74 (c.256G>A; p.Gly86Ser) affects mRNA splicing and produces mutant IFT74 proteins with abnormal subcellular localization along the sperm flagellum, causing male infertility with multiple morphological abnormalities of the sperm flagellum (MMAF) without syndromic features. Exome sequencing, RT-PCR/splicing analysis, immunofluorescence localization of mutant IFT74 along sperm flagellum Human genetics Medium 33689014
2023 An IFT74 exon-2 deletion (removing the first 40 aa) produces truncated IFT74 that still interacts as part of the IFT-B complex but with reduced interaction levels and not with all usual IFT-B partners, as assessed by affinity purification mass spectrometry. Affinity purification mass spectrometry of exon-2-deleted IFT74, patient nasal epithelial cell analysis, electron microscopy Human molecular genetics Medium 37555648
2021 Loss of Ift74 in zebrafish causes ciliogenesis defects; the connecting cilia of photoreceptors initially form but fail to maintain, resulting in slow opsin transport and gradual photoreceptor degeneration, distinct from the rapid degeneration seen in other ift-b mutants. Zebrafish ift74 mutant analysis, opsin immunofluorescence, live imaging of cilia International journal of molecular sciences Medium 34502236

Source papers

Stage 0 corpus · 22 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 Characterization of the intraflagellar transport complex B core: direct interaction of the IFT81 and IFT74/72 subunits. The Journal of biological chemistry 154 15955805
2006 Analysis of IFT74 as a candidate gene for chromosome 9p-linked ALS-FTD. BMC neurology 67 17166276
2000 Analysis of genes under the downstream control of the t(8;21) fusion protein AML1-MTG8: overexpression of the TIS11b (ERF-1, cMG1) gene induces myeloid cell proliferation in response to G-CSF. Blood 66 10887131
2015 Assembly of IFT trains at the ciliary base depends on IFT74. Current biology : CB 62 26051893
2001 Expression of cmg1, an exo-beta-1,3-glucanase gene from Coniothyrium minitans, increases during sclerotial parasitism. Applied and environmental microbiology 38 11157256
2021 Disrupted intraflagellar transport due to IFT74 variants causes Joubert syndrome. Genetics in medicine : official journal of the American College of Medical Genetics 33 33531668
2022 Impaired cooperation between IFT74/BBS22-IFT81 and IFT25-IFT27/BBS19 causes Bardet-Biedl syndrome. Human molecular genetics 31 34888642
2021 A missense mutation in IFT74, encoding for an essential component for intraflagellar transport of Tubulin, causes asthenozoospermia and male infertility without clinical signs of Bardet-Biedl syndrome. Human genetics 25 33689014
1992 Mitogen-induced expression of the primary response gene cMG1 in a rat intestinal epithelial cell-line (RIE-1). FEBS letters 21 1628738
2023 IFT74 variants cause skeletal ciliopathy and motile cilia defects in mice and humans. PLoS genetics 19 37315079
1995 Insulin and insulin-like growth factor I stimulate expression of the primary response gene cMG1/TIS11b by a wortmannin-sensitive pathway in RIE-1 cells. FEBS letters 19 7615073
2020 Second case of Bardet-Biedl syndrome caused by biallelic variants in IFT74. European journal of human genetics : EJHG 18 32144365
2021 Third case of Bardet-Biedl syndrome caused by a biallelic variant predicted to affect splicing of IFT74. Clinical genetics 11 33748949
2006 Capillary morphogenesis gene (CMG)-1 is among the genes differentially expressed in mouse male germ line stem cells and embryonic stem cells. Molecular reproduction and development 11 16705683
2021 Loss of Ift74 Leads to Slow Photoreceptor Degeneration and Ciliogenesis Defects in Zebrafish. International journal of molecular sciences 10 34502236
2023 The IFT81-IFT74 complex acts as an unconventional RabL2 GTPase-activating protein during intraflagellar transport. The EMBO journal 9 37606072
2021 Case Report: Second Report of Joubert Syndrome Caused by Biallelic Variants in IFT74. Frontiers in genetics 9 34539760
2023 Defective airway intraflagellar transport underlies a combined motile and primary ciliopathy syndrome caused by IFT74 mutations. Human molecular genetics 8 37555648
1999 Hypertrophic stimuli augment expression of cMG1/ERF-1, a putative zinc-finger motif transcription factor, in rat cardiomyocytes. FEBS letters 4 10601634
1995 Identification of a functional promoter element in the 5'-flanking region of the rat cMG1/TIS11b gene. The Biochemical journal 4 7575462
2010 Novel role for the intraflagellar transport protein CMG-1 in regulating the transcription of cyclin-D2, E-cadherin and integrin-alpha family genes in mouse spermatocyte-derived cells. Genes to cells : devoted to molecular & cellular mechanisms 2 20545763
2023 IFT74 variants cause skeletal ciliopathy and motile cilia defects in mice and humans. medRxiv : the preprint server for health sciences 0 36865301