Affinage

SFI1

Protein SFI1 homolog · UniProt A8K8P3

Round 2 corrected
Length
1242 aa
Mass
147.7 kDa
Annotated
2026-04-28
58 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SFI1 is a conserved centrin-binding scaffold protein that organizes centrosome/spindle pole body (SPB) architecture and licenses centrosome duplication across eukaryotes. Its multiple internal repeats each bind one molecule of centrin (Cdc31/CETN2) in a 1:1 stoichiometry, forming elongated arrays that constitute the SPB half-bridge in yeast and the distal centriolar ring in human cells; Cdk1 phosphorylation of the Sfi1 C-terminus drives bridge dimerization and SPB separation, while the phosphatase Cdc14 opposes this to reset duplication licensing, and CK2 phosphorylation of centrin negatively regulates centrin–Sfi1 binding (PMID:14504268, PMID:25340401, PMID:24918055). In budding yeast, the Sfi1 N-terminus recruits SPB components Spc29 and Spc42 to initiate daughter SPB assembly, with Cdc31 binding promoting Spc29 recruitment (PMID:33523111). In mammalian cells, SFI1 localizes to the centriole distal end where it recruits USP9X to deubiquitylate and stabilize STIL for centriole duplication during S phase, and the SFI1/Centrin complex is dispensable for duplication per se but essential for centriolar architecture, CEP164 positioning, and CP110 removal during ciliogenesis (PMID:31197030, PMID:36125182).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1999 Medium

    Establishing that SFI1 is an essential gene required for progression through mitosis resolved its role beyond its original identification as a suppressor of cAMP pathway deficiency, placing it in the cell division machinery.

    Evidence Conditional sfi1 mutants in budding yeast arrest with undivided nuclei and no mitotic spindles

    PMID:10455233

    Open questions at the time
    • Molecular target of Sfi1 unknown at this stage
    • No mechanism for spindle assembly failure identified
  2. 2003 High

    Identification of Sfi1p as a multi-centrin scaffold at the SPB half-bridge established the molecular basis by which centrin is organized into functional arrays and explained why Sfi1 is required for SPB duplication.

    Evidence Centrin pull-down, localization to the SPB half-bridge, temperature-sensitive mutant phenotypes, and genetic interaction with cdc31-1 in budding yeast; conservation confirmed with human Sfi1 repeat–centrin binding

    PMID:14504268

    Open questions at the time
    • No structural information on the repeat–centrin interface
    • Mechanism of SPB duplication initiation not resolved
  3. 2007 Medium

    Demonstrating that the C-terminal domain of Sfi1 controls SPB separation (bridge splitting) rather than initial duplication revealed functionally distinct roles for different Sfi1 domains in the centrosome cycle.

    Evidence C-terminal sfi1 alleles from a mad1 synthetic-lethal screen yield duplicated but unseparated SPBs by light and electron microscopy

    PMID:17392514

    Open questions at the time
    • Identity of the C-terminal binding partner mediating splitting unknown
    • Regulation of the splitting step not addressed
  4. 2014 High

    Showing that Cdk1 phosphorylation of Sfi1 licenses once-per-cycle SPB duplication, counteracted by Cdc14 dephosphorylation, established a phospho-regulatory switch ensuring centrosome copy-number control.

    Evidence Phosphomimetic and phospho-null Sfi1 mutants in budding yeast combined with mass spectrometry and live-cell imaging

    PMID:25340401

    Open questions at the time
    • How phosphorylation physically blocks or permits C-terminal dimerization not structurally resolved
    • Contribution of additional kinases not excluded
  5. 2014 High

    Identification that conserved tryptophan residues in Sfi1 repeats are essential for proper Sfi1 partitioning between daughter SPBs linked Sfi1 stoichiometry to spindle bipolarity in fission yeast.

    Evidence Trp-to-Arg mutagenesis with live-cell imaging and EM in S. pombe

    PMID:25031431

    Open questions at the time
    • Whether the tryptophans mediate centrin binding or intra-Sfi1 contacts not distinguished
    • Mechanism of asymmetric partitioning unclear
  6. 2014 High

    CK2 phosphorylation of centrin at T138/S158 was shown to abolish centrin–Sfi1 binding, revealing an additional kinase-mediated layer of regulation of the Sfi1–centrin array independent of Cdk1.

    Evidence In vitro CK2 kinase assay and isothermal titration calorimetry with phosphomimetic human centrin 2

    PMID:24918055

    Open questions at the time
    • In vivo relevance of CK2-mediated centrin phosphorylation for centrosome biology not demonstrated
    • Whether CK2 regulation is cell-cycle dependent is unknown
  7. 2015 High

    Characterization of Kar1 as a direct binding partner of the Sfi1 C-terminus that tethers the bridge to the nuclear envelope, combined with evidence that C-terminal Sfi1 dimerization in G1 is the licensing step for SPB duplication, provided a structural model of bridge formation.

    Evidence Super-resolution PALM imaging, direct binding assays between Kar1 and Sfi1 C-terminal fragments, and bridge morphology in kar1Δ cells in budding yeast

    PMID:26076691

    Open questions at the time
    • Atomic-resolution structure of the Sfi1 C-terminal dimer interface lacking
    • How Cdk1 phosphorylation physically disrupts the dimer not determined
  8. 2015 High

    Demonstrating that Cdc31 phosphorylation on S15 promotes Sfi1 dissociation from the bridge in fission yeast established that centrin phosphorylation actively regulates bridge dynamics and timing of SPB segregation.

    Evidence Phosphomimetic/phospho-null Cdc31 S15 mutagenesis with quantitative live-cell fluorescence and mass spectrometry in S. pombe

    PMID:25736294

    Open questions at the time
    • Whether mammalian centrin phosphorylation plays an equivalent role at the centriole unknown
    • Relationship between CK2-mediated (T138) and Cdk-mediated (S15) phosphorylation not integrated
  9. 2019 High

    Discovery that mammalian SFI1 recruits the deubiquitylase USP9X to the centrosome to stabilize STIL extended Sfi1's function beyond structural scaffolding to active regulation of centriole duplication via ubiquitin signaling.

    Evidence Reciprocal co-immunoprecipitation, deubiquitylation assays, patient cell analysis, and RNAi knockdown in human cells

    PMID:31197030

    Open questions at the time
    • Domain of SFI1 that binds USP9X not mapped
    • Whether the SFI1–USP9X axis operates in non-neural tissues not tested
  10. 2021 High

    Identification of the Sfi1 N-terminus as the direct binding partner of SPB core components Spc29 and Spc42 resolved how Sfi1–Cdc31 arrays nucleate the earliest step of daughter SPB biogenesis (satellite formation), with N-terminal phosphorylation acting as an inhibitory timer.

    Evidence Yeast two-hybrid, co-immunoprecipitation, in vivo localization, and phosphomutant analysis in budding yeast

    PMID:33523111

    Open questions at the time
    • Identity of the kinase responsible for inhibitory N-terminal phosphorylation not fully resolved
    • Stoichiometry of the N-Sfi1/Spc29/Spc42 assembly not quantified
  11. 2022 High

    Super-resolution mapping of human SFI1 to the centriole distal end, and demonstration that its depletion disrupts centriolar architecture, CEP164 positioning, and ciliogenesis without blocking duplication, defined a mammalian structural role for SFI1/Centrin distinct from its duplication-licensing function.

    Evidence Expansion microscopy, siRNA depletion, and ciliogenesis assays in human cells

    PMID:36125182

    Open questions at the time
    • How SFI1/Centrin loss specifically impairs CP110 removal is mechanistically unclear
    • Whether SFI1's structural and USP9X-recruiting functions are separable not tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key open questions include how SFI1's structural scaffold role at the centriole distal end relates to its S-phase role in USP9X recruitment, what the atomic structure of the SFI1–centrin array looks like in situ, and whether mammalian SFI1 phosphoregulation mirrors the yeast Cdk1/Cdc14 licensing switch.
  • No in situ or high-resolution structure of the full-length SFI1–centrin array
  • Mammalian phosphoregulation of SFI1 during the centrosome cycle uncharacterized
  • Relationship between centriole distal-end architecture and ciliogenesis signaling not mechanistically resolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 4 GO:0060090 molecular adaptor activity 2
Localization
GO:0005815 microtubule organizing center 8
Pathway
R-HSA-1640170 Cell Cycle 4 R-HSA-1852241 Organelle biogenesis and maintenance 4
Partners
CDC31CEP164CETN2KAR1SPC29SPC42STILUSP9X
Complex memberships
Sfi1-centrin (Sfi1-Cdc31) half-bridge/bridge array

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 Yeast Sfi1p localizes to the half-bridge of the spindle pole body (SPB) and contains multiple internal repeats that each bind one molecule of the centrin Cdc31p in a 1:1 ratio, such that a single Sfi1p molecule binds multiple centrin molecules. Temperature-sensitive sfi1 mutants show a defect in SPB duplication and genetic interactions with cdc31-1, establishing Sfi1p as an essential component required for SPB duplication. Human proteins containing Sfi1 repeats also bind centrin, demonstrating conservation of this centrin-binding motif. Centrin pull-down experiments, temperature-sensitive mutant analysis, immunofluorescence localization, genetic interaction with cdc31-1 The Journal of cell biology High 14504268
1999 SFI1 is an essential yeast gene required for cell cycle progression through G2-M transition. Conditional sfi1 mutants arrest as doublets of undivided mother-daughter cells with a single nucleus and no mitotic spindles, indicating a role in mitotic spindle assembly. SFI1 was originally identified as a suppressor of cAMP pathway deficiency (fil1 mutant) but acts independently of the cAMP pathway. Conditional expression (galactose-inducible promoter), cell cycle arrest phenotype analysis, genetic epistasis with cAMP pathway mutants Yeast (Chichester, England) Medium 10455233
2007 Novel sfi1 alleles in the C-terminal domain of Sfi1p (identified via mad1 synthetic lethal screen) cause duplicated SPBs that fail to separate (SPBs <0.3 µm apart), suggesting a role for the Sfi1p C-terminal domain in SPB splitting/bridge dissolution distinct from the earlier duplication step. Genetic screen (mad1 synthetic lethal), light and electron microscopy of SPB morphology Molecular biology of the cell Medium 17392514
2014 Cdk1 phosphorylation of Sfi1 licenses yeast centrosome (SPB) duplication to occur only once per cell cycle. Reducing Cdk1 phosphorylation by changing Sfi1 phosphorylation sites to non-phosphorylatable residues causes defects in SPB separation and inappropriate SPB reduplication during mitosis, with bipolar spindle assembly and chromosome segregation defects. The phosphatase Cdc14 opposes Cdk1 by dephosphorylating Sfi1 to activate duplication licensing. Phosphomimetic/phospho-null mutagenesis of Sfi1 phosphorylation sites, live-cell imaging, quantitative mass spectrometry of phosphorylation sites PLoS genetics High 25340401
2014 In fission yeast, Sfi1 is gradually recruited to SPBs throughout the cell cycle (not abruptly at duplication onset). Conserved tryptophan residues in the internal repeats are functionally essential: the Trp-to-Arg mutant (sfi1-M46) forms monopolar spindles, causes mitosis and cytokinesis defects, and associates preferentially with one daughter SPB during mitosis, resulting in failure of new SPB assembly in the SPB receiving insufficient Sfi1. These tryptophans are required for proper Sfi1 partitioning between daughter SPBs. Live-cell fluorescence microscopy (Sfi1-GFP), tryptophan-to-arginine mutagenesis, spindle assembly assays, electron microscopy Molecular biology of the cell High 25031431
2015 In fission yeast, Sfi1 and Cdc31 form the SPB half-bridge that duplicates to promote new SPB biogenesis. Sfi1 accumulates in two distinct cell-cycle phases. Cdc31 phosphorylation on serine 15 (a Cdk1/Cdc2 consensus site) is required for dissociation of a significant pool of Sfi1 from the bridge and for timely SPB segregation at mitotic onset, indicating that Cdc31 N-terminus modulates the stability of Sfi1-Cdc31 arrays and timing of spindle bipolarity. Phosphomimetic/phospho-null mutagenesis of Cdc31 S15, quantitative live-cell fluorescence microscopy, mass spectrometry (phosphoproteomics) Journal of cell science High 25736294
2015 Kar1 (membrane-anchored SPB component) directly binds the C-terminal region of Sfi1 and localizes to the bridge center. Kar1 tethers the Sfi1-containing bridge to the nuclear envelope. In kar1Δ cells the bridge adopts an arched conformation. Sfi1 C-terminal dimerization in G1 is the licensing step for SPB duplication (bridge formation), and Cdc31 and Kar1 provide cross-links that stabilize the bridge and ensure timely SPB separation. Photo-activated localization microscopy (PALM), direct binding assays between Kar1 and Sfi1 C-terminal fragments, binding free energy calculations The Journal of cell biology High 26076691
2014 CK2 phosphorylates human centrin 1 at T138 and human centrin 2 at T138 and S158. These phosphorylation events reduce or abolish centrin binding to Sfi1 (as well as to XPC and transducin β), as demonstrated by phosphomimetic centrin 2 (T138D-S158D) which completely abrogates Sfi1 binding. This places CK2 as a writer that negatively regulates centrin-Sfi1 interaction. In vitro CK2 phosphorylation assay, isothermal titration calorimetry (ITC) binding measurements, phosphomimetic mutagenesis FEBS open bio High 24918055
2019 Mammalian SFI1 localizes to the centrosome during S phase and interacts with the deubiquitylase USP9X. SFI1 recruits USP9X to the centrosome, where USP9X deubiquitylates STIL (a critical regulator of centriole duplication), protecting it from proteasomal degradation. Loss of USP9X (from patient mutations) reduces STIL levels. This SFI1→USP9X→STIL axis promotes centriole duplication and underlies roles of both SFI1 and USP9X in human neurodevelopment. Co-immunoprecipitation, centrosome localization experiments, ubiquitylation/deubiquitylation assays, patient cell analysis, RNAi knockdown with phenotypic readout The Journal of cell biology High 31197030
2021 The N-terminus of Sfi1 (N-Sfi1), including the first three Cdc31-binding sites, directly interacts with SPB components Spc29 and Spc42 to trigger daughter SPB (dSPB) assembly. Cdc31 binding to N-Sfi1 promotes Spc29 recruitment and is essential for satellite formation (earliest step of dSPB biogenesis). Phosphorylation of N-Sfi1 has an inhibitory effect, delaying dSPB biogenesis until G1. Yeast two-hybrid, co-immunoprecipitation, in vivo localization, phosphomutant analysis The Journal of cell biology High 33523111
2022 Human SFI1 is a centriolar protein that localizes to the distal end of the centriole, where it associates with a pool of Centrin. Both SFI1 and Centrin are recruited early during procentriole assembly. Depletion of SFI1 causes loss of the distal Centrin pool without altering centriole duplication per se; instead, the SFI1/Centrin complex is essential for centriolar architecture, CEP164 distribution, and CP110 removal during ciliogenesis. Expansion microscopy (ExM), siRNA depletion, fluorescence localization, ciliogenesis assays The EMBO journal High 36125182
2025 C2CD3 depletion in human centrioles destabilizes a luminal ring network composed of C2CD3/SFI1/centrin-2/CEP135/NA14, revealing that SFI1 is a structural component of the luminal ring at the distal centriole. This network connects the centriolar lumen, distal microtubule cap, and appendages in an 'in-to-out' molecular hub. Ultrastructure Expansion Microscopy (U-ExM), iterative U-ExM, in situ cryo-electron tomography, siRNA depletion bioRxivpreprint Medium bio_10.1101_2025.06.17.660204

Source papers

Stage 0 corpus · 58 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 Towards a proteome-scale map of the human protein-protein interaction network. Nature 2090 16189514
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2005 Chromosome-wide mapping of estrogen receptor binding reveals long-range regulation requiring the forkhead protein FoxA1. Cell 1126 16009131
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2014 A proteome-scale map of the human interactome network. Cell 977 25416956
2003 Complete sequencing and characterization of 21,243 full-length human cDNAs. Nature genetics 754 14702039
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
1995 Cell cycle regulation of the activity and subcellular localization of Plk1, a human protein kinase implicated in mitotic spindle function. The Journal of cell biology 427 7790358
2005 Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes. Genome research 409 16344560
2021 A proximity-dependent biotinylation map of a human cell. Nature 339 34079125
2009 Docking motif-guided mapping of the interactome of protein phosphatase-1. Chemistry & biology 269 19389623
2003 Polo-like kinase 1 regulates Nlp, a centrosome protein involved in microtubule nucleation. Developmental cell 216 12852856
2011 Next-generation sequencing to generate interactome datasets. Nature methods 200 21516116
2002 Centrosomal proteins CG-NAP and kendrin provide microtubule nucleation sites by anchoring gamma-tubulin ring complex. Molecular biology of the cell 190 12221128
2000 The centrosomal protein C-Nap1 is required for cell cycle-regulated centrosome cohesion. The Journal of cell biology 187 11076968
2000 Functional analysis of the human CDC5L complex and identification of its components by mass spectrometry. The EMBO journal 179 11101529
2003 Sfi1p has conserved centrin-binding sites and an essential function in budding yeast spindle pole body duplication. The Journal of cell biology 168 14504268
1998 Prediction of the coding sequences of unidentified human genes. IX. The complete sequences of 100 new cDNA clones from brain which can code for large proteins in vitro. DNA research : an international journal for rapid publication of reports on genes and genomes 156 9628581
2006 The PITSLRE/CDK11p58 protein kinase promotes centrosome maturation and bipolar spindle formation. EMBO reports 120 16462731
2011 A whole genome screen for HIV restriction factors. Retrovirology 111 22082156
2018 Histone Interaction Landscapes Visualized by Crosslinking Mass Spectrometry in Intact Cell Nuclei. Molecular & cellular proteomics : MCP 101 30021884
2016 Pooled-matrix protein interaction screens using Barcode Fusion Genetics. Molecular systems biology 89 27107012
2014 Genome-wide association analysis demonstrates the highly polygenic character of age-related hearing impairment. European journal of human genetics : EJHG 78 24939585
2018 Aurora B opposes PP1 function in mitosis by phosphorylating the conserved PP1-binding RVxF motif in PP1 regulatory proteins. Science signaling 68 29764992
2018 The homozygous variant c.797G>A/p.(Cys266Tyr) in PISD is associated with a Spondyloepimetaphyseal dysplasia with large epiphyses and disturbed mitochondrial function. Human mutation 61 30488656
2010 Direct interaction between hnRNP-M and CDC5L/PLRG1 proteins affects alternative splice site choice. EMBO reports 59 20467437
2019 PISD is a mitochondrial disease gene causing skeletal dysplasia, cataracts, and white matter changes. Life science alliance 57 30858161
2020 RIG-I regulates myeloid differentiation by promoting TRIM25-mediated ISGylation. Proceedings of the National Academy of Sciences of the United States of America 47 32513696
2022 NUDT21 limits CD19 levels through alternative mRNA polyadenylation in B cell acute lymphoblastic leukemia. Nature immunology 46 36138187
2014 Regulation of spindle pole body assembly and cytokinesis by the centrin-binding protein Sfi1 in fission yeast. Molecular biology of the cell 33 25031431
2014 Licensing of yeast centrosome duplication requires phosphoregulation of sfi1. PLoS genetics 33 25340401
2015 Cell cycle control of spindle pole body duplication and splitting by Sfi1 and Cdc31 in fission yeast. Journal of cell science 27 25736294
2007 Novel sfi1 alleles uncover additional functions for Sfi1p in bipolar spindle assembly and function. Molecular biology of the cell 26 17392514
2022 Human SFI1 and Centrin form a complex critical for centriole architecture and ciliogenesis. The EMBO journal 25 36125182
2015 The insecticidal spider toxin SFI1 is a knottin peptide that blocks the pore of insect voltage-gated sodium channels via a large β-hairpin loop. The FEBS journal 22 25559770
2019 SFI1 promotes centriole duplication by recruiting USP9X to stabilize the microcephaly protein STIL. The Journal of cell biology 18 31197030
2015 Kar1 binding to Sfi1 C-terminal regions anchors the SPB bridge to the nuclear envelope. The Journal of cell biology 17 26076691
2014 CK2 phosphorylation of human centrins 1 and 2 regulates their binding to the DNA repair protein XPC, the centrosomal protein Sfi1 and the phototransduction protein transducin β. FEBS open bio 15 24918055
2013 Sfr13, a member of a large family of asymmetrically localized Sfi1-repeat proteins, is important for basal body separation and stability in Tetrahymena thermophila. Journal of cell science 15 23426847
1999 Deletion of SFI1, a novel suppressor of partial Ras-cAMP pathway deficiency in the yeast Saccharomyces cerevisiae, causes G(2) arrest. Yeast (Chichester, England) 14 10455233
2004 Towards developing a protein infrared spectra databank (PISD) for proteomics research. Proteomics 12 15274125
2021 The N-terminus of Sfi1 and yeast centrin Cdc31 provide the assembly site for a new spindle pole body. The Journal of cell biology 8 33523111
2016 New insights into the interaction of centrin with Sfi1. Biochimica et biophysica acta 8 26779587
2023 An Sfi1-like centrin-interacting centriolar plaque protein affects nuclear microtubule homeostasis. PLoS pathogens 7 37130129
2022 Conformational Plasticity of Centrin 1 from Toxoplasma gondii in Binding to the Centrosomal Protein SFI1. Biomolecules 7 36009009
2020 Knockdown of TFAM in Tumor Cells Retarded Autophagic Flux through Regulating p53 Acetylation and PISD Expression. Cancers 6 32093281
2024 Fishnet mesh of centrin-Sfi1 drives ultrafast calcium-activated contraction of the giant cell Spirostomum ambiguum. bioRxiv : the preprint server for biology 5 39574644
2023 Long non-coding RNA in coronary artery disease: the role of PDXDC1-AS1 and SFI1-AS1. Functional & integrative genomics 4 37394483
2016 Sfr1, a Tetrahymena thermophila Sfi1 Repeat Protein, Modulates the Production of Cortical Row Basal Bodies. mSphere 4 27904881
2013 The E144 residue of Scherffelia dubia centrin discriminates between the DNA repair protein XPC and the centrosomal protein Sfi1. FEBS open bio 4 24371720
2024 Novel biallelic PISD missense variants cause spondyloepimetaphyseal dysplasia with disproportionate short stature and fragmented mitochondrial morphology. Clinical genetics 3 38801004
2025 Spatiotemporal control of cortical centrin patterning by regionalized Sfi1 family scaffolding proteins in Stentor coeruleus. bioRxiv : the preprint server for biology 1 40832266
2016 A chirality change in XPC- and Sfi1-derived peptides affects their affinity for centrin. Peptides 1 26923803
2025 Nano polystyrene accelerated the reproductive toxicity induced by the Tris(1,3-dichloro-2-propyl) phosphate via Nhr-69-PISD-Drp-1-mediated mitochondrial fragmentation in Caenorhabditis elegans. Environmental pollution (Barking, Essex : 1987) 0 40744371
2025 Mechanism of PISD/SPG7-mediated mPTP opening in necroptosis of inflammatory HaCaT cells induced by nano-zinc oxide. Toxicology 0 40780696