fmc1 (Formation of Mitochondrial Complexes protein 1; systematic name SPAC1486.11) is a small (104-residue) mitochondrial protein of fission yeast belonging to the FMC1 family (InterPro IPR039196; PANTHER PTHR28015), a group within the LYR-motif protein (LYRM / Complex1_LYR_2, Pfam PF13233) superfamily of mitochondrial accessory and assembly factors. It carries a predicted N-terminal mitochondrial targeting sequence and is imported into the mitochondrion. By orthology to the well-characterized Saccharomyces cerevisiae Fmc1p, it is inferred to be a soluble matrix protein that acts as an accessory assembly factor for the F1 sector (the catalytic alpha3beta3 head) of the mitochondrial F1Fo-ATP synthase (Complex V), most plausibly by assisting the folding, stability or function of the dedicated F1 assembly chaperone Atp12 (human ATPAF2). In budding yeast this requirement is conditional, becoming critical at elevated temperature, where loss of Fmc1p causes the newly imported alpha-F1 and beta-F1 subunits to aggregate in the matrix instead of assembling into functional F1. The fission-yeast protein itself has not been functionally characterized; its specific molecular activity, partners and loss-of-function phenotype remain undetermined.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005759 mitochondrial matrix | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Matrix localization is well supported at the family level: the characterized S. cerevisiae ortholog is a soluble matrix protein, and the matrix is the compartment where the F1 alpha3beta3 head is assembled. fmc1 carries a predicted mitochondrial transit peptide. Kept as a correct, informative localization, but treated as non-core because it has not been shown experimentally for the pombe protein. Reason: IBA propagated from SGD:S000001360; consistent with the founding paper showing Fmc1p is a soluble matrix protein, and with the predicted N-terminal transit peptide. Correct and specific, but the localization of the pombe protein is inferred, not experimentally demonstrated. Supporting Evidence: PMID:11096112 Fmc1p is a soluble protein located in the mitochondrial matrix. |
| GO:0033615 mitochondrial proton-transporting ATP synthase complex assembly | IBA GO_REF:0000033 | ACCEPT | Summary: This is the best-supported functional statement for fmc1 and represents its core biological role: participation in assembly of the mitochondrial proton-transporting ATP synthase (Complex V). The term is directly supported by the family-defining function established for the S. cerevisiae ortholog and by the InterPro/PANTHER family assignment. Retained as core. Reason: Family-defining biological process, propagated by phylogeny (IBA from SGD:S000001360) and independently supported by the InterPro Fmc1 signature. Matches the founding paper, in which Fmc1p is required for assembly/stability of the F1 sector of ATP synthase. Supporting Evidence: PMID:11096112 We have identified a yeast nuclear gene (FMC1) that is required at elevated temperatures (37 degrees C) for the formation/stability of the F(1) sector of the mitochondrial ATP synthase. |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Correct but general parent term derived from the UniProt Subcellular Location mapping (SL-0173, Mitochondrion). It is subsumed by the more specific mitochondrial matrix annotation, so it is kept as non-core. Reason: Accurate compartment assignment consistent with the predicted transit peptide, but less informative than GO:0005759 (mitochondrial matrix); redundant parent. |
| GO:0033615 mitochondrial proton-transporting ATP synthase complex assembly | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO annotation from the Fmc1 signature (IPR039196), giving the same ATP-synthase-assembly process as the IBA annotation. It corroborates the core biological process from an independent (domain-based) line of evidence. Reason: Domain-based support (InterPro IPR039196 -> GO:0033615) that is concordant with the phylogenetic (IBA) annotation and with the family function; a well-founded electronic annotation to the core process. |
| GO:0003674 molecular_function | ND GO_REF:0000015 | KEEP AS NON CORE | Summary: Root molecular_function annotation with the ND (No biological Data) evidence code, correctly flagging that no specific molecular activity has been determined for fmc1. This honestly reflects the state of knowledge: the molecular function is genuinely dark. See knowledge_gaps and core_functions for the orthology-based inference of a chaperone-like assembly-factor activity. Reason: Legitimate ND placeholder; the specific molecular function of fmc1 is undetermined. It should not be removed, as it accurately records that the MF aspect is uncurated/unknown rather than annotated to a specific activity. |
| GO:0044183 protein folding chaperone | ISS PMID:11096112 Identification of a nuclear gene (FMC1) required for the ass... | NEW | Summary: Proposed molecular function inferred by orthology (not present in the current GOA). The characterized S. cerevisiae ortholog assists the folding/stability or function of the F1 assembly chaperone Atp12p, a non-catalytic chaperone-like activity that fits the FMC1/LYR-motif family (no catalytic domain). Offered as the most defensible specific MF to replace the ND placeholder, pending experimental confirmation in fission yeast. Reason: fmc1 has no annotated specific molecular function (MF is ND). A protein-folding chaperone activity is the best-supported inference from the family-defining function of the S. cerevisiae ortholog and from the domain architecture; not ATP-dependent (no ATPase), so GO:0044183 rather than GO:0140662. Marked ISS and non-verified for the pombe protein. Note this is a second-order inference: the founding data show Fmc1p acts on the F1 assembly chaperone Atp12p, so a competing hypothesis is that fmc1 is not itself the folding chaperone but an adaptor/stabilizer of a partner chaperone (e.g. GO:0051087 protein-folding chaperone binding); the two cannot be distinguished without direct assays (see knowledge_gaps). Supporting Evidence: PMID:11096112 We propose that Fmc1p is required for the proper folding/stability or functioning of Atp12p in heat stress conditions. |
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Download this section (compressed HTML)Q: Does S. pombe fmc1 physically interact with a fission-yeast Atp12/ATPAF2 ortholog and with the F1 alpha/beta subunits, and is its requirement for ATP synthase assembly conditional (e.g. heat-stress specific) as in budding yeast?
Experiment: Construct an fmc1-null strain and assess respiratory competence and growth on a non-fermentable carbon source at normal and elevated temperature; quantify assembled F1Fo-ATP synthase (blue-native PAGE / activity assays) and test for accumulation/aggregation of unassembled alpha-F1 and beta-F1 subunits in the matrix. Complement with tagged-protein pulldowns to identify the pombe Atp12 ortholog and F1 subunits as interaction partners.
Hypothesis: fmc1 is required for assembly of the F1 sector of mitochondrial ATP synthase in S. pombe, acting through the Atp12/ATPAF2 assembly chaperone.
Type: genetics and biochemistry
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The specific molecular activity of the fission-yeast fmc1 protein is undetermined. Whether it acts as a protein-folding chaperone in its own right, as an adaptor that stabilizes a partner chaperone (an Atp12/ATPAF2 ortholog), or in some other capacity has not been shown; the GO molecular_function is ND.
OPEN BIOLOGY MF_DARK
What is known: The protein is confidently placed in the FMC1 family (InterPro IPR039196, PANTHER PTHR28015) and carries a single LYR-motif (Complex1_LYR_2) module and a predicted mitochondrial transit peptide, implying a non-catalytic accessory role in ATP synthase assembly. The founding S. cerevisiae study established that the ortholog assists folding/stability or function of the F1 assembly chaperone Atp12p.
Significance: Pinning down the molecular activity would convert an orthology-based inference into an experimentally grounded function and clarify how the LYR-motif fold of FMC1-family proteins contributes to Complex V biogenesis.
What would resolve it: Biochemical characterization of the pombe protein (e.g. interaction/complex assays with the pombe Atp12/ATPAF2 ortholog and F1 subunits; in-organello F1 assembly assays in an fmc1-null background).
Provenance (the field's own admissions):
Gap: It is not known whether the F1-ATP-synthase-assembly role attributed to fmc1 is demonstrated in S. pombe or is purely inferred by orthology. All fission-yeast GO annotations are electronic or phylogenetic (IBA/IEA); none are experimental.
OPEN BIOLOGYCURATION MF_DARK
What is known: In S. cerevisiae the assembly role is experimentally established, including the aggregation of alpha/beta-F1 subunits on loss of Fmc1p and rescue by Atp12p overexpression. UniProt records the pombe protein only at transcript level (Evidence at transcript level, PE 2).
Significance: Distinguishing demonstrated from inferred function prevents over-reading the IBA/IEA annotations as direct evidence and identifies the pombe protein as a target for experimental validation.
Provenance (the field's own admissions):
Gap: No loss-of-function phenotype has been reported for S. pombe fmc1, and it is unknown whether (as in budding yeast) its requirement is conditional (heat-stress specific) or broader, and whether a functional Atp12/ATPAF2 partner exists and is engaged in fission yeast.
OPEN BIOLOGY BP_DARK
What is known: In S. cerevisiae, Fmc1p is dispensable at normal growth temperature (28-30 C) but required at 37 C, and its loss is compensated by Atp12p overexpression; no equivalent conditional-phenotype or partner data exist for the pombe gene.
Significance: A conditional (stress-dependent) versus constitutive requirement changes how the gene should be annotated for biological process and regulation, and whether an ATP-synthase-assembly defect is the primary phenotype.
Provenance (the field's own admissions):
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