Tim10 is a small Tim family protein that functions as a subunit of the heterohexameric Tim9-Tim10 chaperone complex (3:3 stoichiometry) in the mitochondrial intermembrane space (IMS). The complex acts as an ATP-independent chaperone that binds hydrophobic precursor proteins, particularly mitochondrial carrier family proteins (SLC25/ADP-ATP carrier type), as they emerge from the TOM complex in the outer membrane and escorts them to the TIM22 translocase for insertion into the inner membrane. Tim10 contains a characteristic twin CX3C motif that forms two intramolecular disulfide bonds in the oxidizing IMS environment. The Tim9-Tim10 hexamer adopts a six-bladed alpha-propeller structure with tentacle-like helices that engage hydrophobic client proteins. Function inferred from highly conserved small Tim biology across fungi and metazoans [PMID:16387659, Tim10-deep-research-falcon.md].
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0042721 TIM22 mitochondrial import inner membrane insertion complex | IBA GO_REF:0000033 | MODIFY | Summary: This annotation places Tim10 as part of the TIM22 complex. While Tim9-Tim10 does transiently associate with TIM22 to deliver substrates, the soluble Tim9-Tim10 hexamer is primarily localized in the IMS as a distinct chaperone complex, not as a permanent subunit of TIM22. The GO term GO:0042719 (mitochondrial intermembrane space chaperone complex) more accurately describes the primary location of Tim10. The TIM22 complex definition explicitly mentions Tim9-Tim10-Tim12 as peripheral components, so this annotation is technically defensible but may be misleading about the primary localization [PMID:16387659, PMID:14726512, Tim10-deep-research-falcon.md]. Reason: Tim10 is primarily a component of the soluble Tim9-Tim10 IMS chaperone complex, not the membrane-embedded TIM22 complex. While there is transient association with TIM22 during substrate handoff, GO:0042719 (mitochondrial intermembrane space chaperone complex) is more accurate for describing Tim10's primary localization. Proposed replacements: mitochondrial intermembrane space chaperone complex Supporting Evidence: PMID:16387659 They coassemble into a hexamer, TIM9.10, which captures and chaperones precursors of inner membrane metabolite carriers as they exit the TOM channel in the outer membrane. PMID:14726512 Tim9, Tim10a, and Tim10b are members of the family of small Tim proteins located in the intermembrane space of mammalian mitochondria. file:SCHPO/tim10/tim10-deep-research-falcon.md [Tim10 forms a heterohexamer with Tim9 in the IMS to chaperone hydrophobic precursors] |
| GO:0032977 membrane insertase activity | IBA GO_REF:0000033 | MODIFY | Summary: This annotation attributes membrane insertase activity to Tim10. However, Tim10 as part of the soluble Tim9-Tim10 complex functions as a chaperone that delivers substrates to TIM22, which contains the actual insertase (Tim22 protein). Tim9-Tim10 does not directly insert proteins into membranes; it protects hydrophobic precursors from aggregation and delivers them to the insertion machinery [PMID:16387659, Tim10-deep-research-falcon.md]. Reason: Tim10 functions as a chaperone, not an insertase. The Tim9-Tim10 complex binds and escorts hydrophobic precursors but does not directly mediate membrane insertion. GO:0140318 (protein transporter activity) would be more appropriate - it explicitly mentions Tim9-Tim10 as an example in its definition. Proposed replacements: protein transporter activity Supporting Evidence: PMID:16387659 The propeller blades are reminiscent of "tentacles" in chaperones Skp and prefoldin. file:SCHPO/tim10/tim10-deep-research-falcon.md [Tim9-Tim10 complex acts as an ATP-independent chaperone for hydrophobic precursors] |
| GO:0045039 protein insertion into mitochondrial inner membrane | IBA GO_REF:0000033 | ACCEPT | Summary: This biological process annotation is appropriate. Tim10 as part of the Tim9-Tim10 complex is directly involved in the pathway leading to protein insertion into the mitochondrial inner membrane. While Tim10 itself does not perform the insertion, it is an essential component of the TIM22 import pathway that delivers carrier protein precursors for insertion [PMID:16387659, PMID:14726512, Tim10-deep-research-falcon.md]. Reason: Tim10 participates in the protein insertion pathway by chaperoning precursors to TIM22. This is a core function of the Tim9-Tim10 complex and is well-documented across eukaryotes. Supporting Evidence: PMID:16387659 Import of proteins into mitochondria occurs by coordinated actions of preprotein translocases in the outer and inner membranes. PMID:14726512 In yeast, members of this family act along the TIM22 import pathway during import of metabolite carriers and other integral inner membrane proteins. file:SCHPO/tim10/tim10-deep-research-falcon.md [Tim10 participates in the TIM22 carrier translocase pathway] |
| GO:0005743 mitochondrial inner membrane | IEA GO_REF:0000044 | MODIFY | Summary: This annotation from UniProt subcellular location mapping is partially accurate but potentially misleading. Tim10 is primarily a soluble IMS protein, though it does associate peripherally with the inner membrane as part of its function [PMID:16387659, PMID:14726512, Tim10-deep-research-falcon.md]. Reason: Tim10 is primarily localized in the mitochondrial intermembrane space as a soluble protein. While it associates peripherally with the inner membrane during substrate handoff to TIM22, its primary localization is the IMS. GO:0005758 (mitochondrial intermembrane space) would be more accurate. Proposed replacements: mitochondrial intermembrane space Supporting Evidence: PMID:16387659 Tim9 and Tim10 are translocase components of the intermembrane space, related to deafness-dystonia peptide 1 (DDP1). PMID:14726512 Tim9, Tim10a, and Tim10b are members of the family of small Tim proteins located in the intermembrane space of mammalian mitochondria. file:SCHPO/tim10/tim10-deep-research-falcon.md [Small Tims are soluble IMS proteins] |
| GO:0015031 protein transport | IEA GO_REF:0000043 | ACCEPT | Summary: This is a correct but overly broad annotation derived from UniProt keyword mapping. Tim10 is indeed involved in protein transport, specifically in chaperoning mitochondrial carrier proteins through the IMS to TIM22 [PMID:16387659, Tim10-deep-research-falcon.md]. Reason: While overly general, this annotation is correct. The more specific GO:0045039 is already present and captures the precise biological process. This IEA annotation can be retained as a broader categorization. Supporting Evidence: PMID:16387659 They coassemble into a hexamer, TIM9.10, which captures and chaperones precursors of inner membrane metabolite carriers as they exit the TOM channel in the outer membrane. file:SCHPO/tim10/tim10-deep-research-falcon.md [Tim9-Tim10 complex delivers hydrophobic precursors to TIM22] |
| GO:0045039 protein insertion into mitochondrial inner membrane | IEA GO_REF:0000117 | ACCEPT | Summary: This is a duplicate of the IBA annotation for the same term (GO:0045039). The ARBA machine learning annotation agrees with the phylogenetic inference, providing independent computational support for Tim10's role in protein insertion into the mitochondrial inner membrane [Tim10-deep-research-falcon.md]. Reason: Duplicate annotation with different evidence source (ARBA vs IBA). Both support the same correct biological process annotation. Retaining both is acceptable as they represent independent computational evidence. Supporting Evidence: PMID:16387659 Import of proteins into mitochondria occurs by coordinated actions of preprotein translocases in the outer and inner membranes. file:SCHPO/tim10/tim10-deep-research-falcon.md [Tim10 is involved in mitochondrial protein import] |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: This annotation reflects the zinc-binding capability of small Tim proteins via their twin CX3C motif. However, in the mature, functional state within the oxidizing IMS environment, the cysteine residues form disulfide bonds rather than coordinating zinc. Zinc binding may occur transiently during cytoplasmic transit before import [PMID:10552927, PMID:16387659, Tim10-deep-research-falcon.md]. Reason: Zinc binding is not the primary function of Tim10. The twin CX3C motif forms disulfide bonds in the mature IMS-localized protein. Zinc coordination may occur transiently during import from the cytoplasm but is not the functional state. Supporting Evidence: PMID:10552927 It bears a strong resemblance to a recently characterized set of zinc-binding yeast proteins (Tim8p, Tim9p, Tim10p, Tim12p, and Tim13p) that are implicated in the import of a class of transmembrane carrier proteins from the cytoplasm to the mitochondrial inner membrane. PMID:16387659 In each TIM9.10 subunit, a signature "twin CX3C" motif forms two intramolecular disulfides. file:SCHPO/tim10/tim10-deep-research-falcon.md [The conserved twin CX3C motif forms disulfide bonds in the IMS] |
| GO:0140309 unfolded protein carrier activity | ISO GO_REF:0000024 | ACCEPT | Summary: This ISO annotation from SGD ortholog transfer accurately captures Tim10's chaperone function. The Tim9-Tim10 complex binds unfolded/partially folded hydrophobic precursor proteins and carries them through the IMS to TIM22 [PMID:16387659, PMID:14726512, Tim10-deep-research-falcon.md]. Reason: This accurately describes Tim10's role in the Tim9-Tim10 chaperone complex. The complex binds hydrophobic precursors in an unfolded state and transports them to TIM22. This is well-supported by structural and biochemical studies. Supporting Evidence: PMID:16387659 There is no obvious binding pocket for precursors, which we suggest employ the chaperone-like tentacles of TIM9.10 as surrogate lipid contacts. PMID:14726512 During import, the small Tim complexes directly interact with human adenine nucleotide translocator (ANT) in transit in a metal-dependent manner. file:SCHPO/tim10/tim10-deep-research-falcon.md [Tim9-Tim10 complex binds and carries unfolded hydrophobic precursors] |
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Download this section (compressed HTML)Q: Is there direct experimental evidence for Tim10 function in S. pombe, or is all functional annotation based on inference from S. cerevisiae and other organisms? The deep research and literature review found no S. pombe-specific experimental studies on Tim10. All functional understanding is inferred from conserved small Tim biology in other organisms.
Q: Does S. pombe Tim10 have additional functions beyond carrier protein chaperoning, such as roles in respiratory complex assembly as seen for some human small TIMs? Recent work (Anderson et al. 2023) showed human Tim8a/8b/13 have roles in Complex IV assembly. It would be interesting to know if S. pombe small Tims have similar expanded functions.
Experiment: Generate S. pombe tim10 deletion or temperature-sensitive mutants to assess essentiality and phenotypes in fission yeast. Tim9 and Tim10 are essential in S. cerevisiae but this has not been directly demonstrated in S. pombe. Mutants are expected to be lethal or show severe mitochondrial carrier protein import defects.
Hypothesis: Tim10 is essential for viability in S. pombe due to its conserved role in mitochondrial carrier protein import.
Experiment: Immunoprecipitation and mass spectrometry of S. pombe Tim10 to identify interaction partners and client proteins. This would confirm Tim9-Tim10 complex formation and identify specific substrates in S. pombe. Expected to co-purify with Tim9 and mitochondrial carrier proteins.
Hypothesis: S. pombe Tim10 forms a conserved hexameric complex with Tim9 and interacts with mitochondrial carrier family proteins as clients.
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