Multi-pass protein of the mitochondrial outer membrane that acts as an insertase for alpha-helical outer-membrane proteins. MTCH1 is the vertebrate paralogue of MTCH2, and both belong to a holozoan-wide clade that retains the six-transmembrane SLC25 (mitochondrial carrier) fold while having diverged from the SLC25 transporters: the clade has lost transporter elements including the interhelical salt bridges required for alternating access, and insertase activity is associated with loss of a transmembrane helix that opens a lipid-accessible hydrophilic groove. Despite the name "mitochondrial carrier homolog", no transported substrate has ever been identified for MTCH1 or MTCH2, and there is no evidence that either protein is a carrier. Insertase capability of MTCH1 itself is supported by depletion phenotypes that are additive with loss of MTCH2 in human cells, by partial rescue of MTCH2 loss in human cells, and by the ability of MTCH1 alone to substitute for the unrelated yeast Mim1/Mim2 (MIM) insertase complex, restoring growth, substrate biogenesis, TOM complex stability and mitochondrial morphology. MTCH1 was originally described as presenilin-associated protein (PSAP), a putative PDZ-like presenilin-1 interactor; that domain assignment has not been borne out. Overexpression of MTCH1 triggers cytochrome c release, caspase-3 activation and apoptosis, but the mechanism connecting this to its insertase activity is not established.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic assertion that MTCH1 acts in the mitochondrion; correct. Reason: Correct. The gene also carries the more specific mitochondrial outer membrane (GO:0005741) annotation, which better describes where MTCH1 sits. Note that MTCH1 itself (UniProtKB:Q9NZJ7) appears in the WITH/FROM list; this is expected and legitimate, since MTCH1's own experimental localisation is one of the descendant evidences the PAINT curator used to place the ancestral assertion. |
| GO:0016020 membrane | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: Root-level membrane term propagated phylogenetically. Reason: Not wrong, but uninformative when the gene already carries mitochondrial outer membrane (GO:0005741). The phylogenetic node placement is not in dispute - every member of the clade is an integral membrane protein - and the objection is purely to the granularity of the term. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: UniProtKB:Q9Y6C9 Β· MTCH2 SUPPORTS TRANSFER Human paralogue; a bona fide mitochondrial outer membrane protein, so the transfer itself is sound. MGI:MGI:1929260 Β· Mtch1 (mouse) SUPPORTS TRANSFER Mouse orthologue; same compartment. PANTHER:PTN001324730 Β· PTN001324730 SUPPORTS TRANSFER Ancestral node for the MTCH clade within PTHR10780; membrane residence is a clade-wide property. |
| GO:0043065 positive regulation of apoptotic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic propagation of the proapoptotic role, seeded in part by MTCH1's own experimental annotation and by the mouse orthologue. Reason: The underlying observation is a gain-of-function phenotype (overexpression of MTCH1/PSAP causes cytochrome c release, caspase-3 activation and apoptosis), reproducible enough that a later study had to add a pan-caspase inhibitor merely to package MTCH1 lentivirus. But no mechanism links it to the established molecular function, and the alternative reading - that disrupting outer-membrane protein biogenesis secondarily triggers apoptosis - has not been excluded. Retained as a genuine but peripheral role rather than a core function. Deliberately NOT merged with the separate MTCH2/BAX-BAK pore literature (PMID:42056306), which has not been tested on MTCH1. Supporting Evidence: PMID:12377771 The mitochondrial localization and proapoptotic activity of PSAP suggest that it is an important regulator of apoptosis. |
| GO:0005741 mitochondrial outer membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Subcellular-location mapping placing MTCH1 in the mitochondrial outer membrane. Reason: Correct and the most specific location supported by the literature; this is where the insertase acts. Supporting Evidence: PMID:36264797 which is also localized to the mitochondrial outer membrane, had an additive effect to loss of MTCH2 on biogenesis of many mitochondrial TAs |
| GO:0032977 membrane insertase activity | IMP PMID:38428433 Triaging of Ξ±-helical proteins to the mitochondrial outer me... | ACCEPT | Summary: Insertase activity of MTCH1, from CRISPRi/knockdown analysis of the machinery required for biogenesis of alpha-helical mitochondrial outer membrane proteins. Reason: Core molecular function. Three independent lines now support it for MTCH1 specifically - an additive depletion phenotype with MTCH2 in human cells (PMID:36264797), partial rescue of MTCH2 loss in human cells (PMID:42308315), and stand-alone complementation of the unrelated yeast MIM complex (PMID:40704594). The last of these is the only experiment that isolates MTCH1 from MTCH2, and it is positive. Supporting Evidence: PMID:40704594 These findings indicate that MTCH1, by itself, has insertase activity and is a functional equivalent for the MIM complex, despite the absence of any evolutionary relation between the mammalian and yeast insertases. |
| GO:7770059 alpha helical protein insertion into mitochondrial outer membrane | IMP PMID:38428433 Triaging of Ξ±-helical proteins to the mitochondrial outer me... | ACCEPT | Summary: The specific process MTCH1 carries out - insertion of alpha-helical (signal-anchored, tail-anchored and polytopic) proteins into the mitochondrial outer membrane. Reason: Core biological process, and the correct level of specificity. MTCH insertases act on alpha-helical substrates and not on beta-barrel proteins. Supporting Evidence: PMID:40704594 Furthermore, MTCH1 could restore the biogenesis of MIM substrates, translocase of the outer membrane (TOM) complex stability and morphology of mitochondria. |
| GO:0005515 protein binding | IPI PMID:40105103 Definition of the human mitochondrial TOM interactome reveal... | REMOVE | Summary: Bare protein binding recorded from a TOM-interactome study (interactor MUL1/MAPL, UniProtKB:Q969V5). Reason: Carries no functional information. The underlying interaction is worth keeping in UniProt SUBUNIT, but as a GO molecular function this term says nothing about what MTCH1 does. No more informative molecular function is supportable from this evidence, so the row is removed rather than rewritten. Removal does not imply the reported interaction is false. |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: High-throughput proteomic assignment of MTCH1 to the mitochondrion. Reason: Correct. The gene also carries the more specific mitochondrial outer membrane (GO:0005741) annotation, which better describes where MTCH1 sits. |
| GO:0032977 membrane insertase activity | IDA PMID:36264797 MTCH2 is a mitochondrial outer membrane protein insertase. | ACCEPT | Summary: Insertase activity assigned to MTCH1 alongside MTCH2 in the study that established the MTCH insertase class. Reason: Core molecular function, and correct - but the evidence code is generous for this particular paper. The reconstitution with purified protein in liposomes was done for MTCH2; for MTCH1 this study shows an additive depletion phenotype and then proposes the class assignment ("We therefore propose that MTCH1/2 are the founding members of a unique class of membrane protein insertases"). The conclusion has since been confirmed directly for MTCH1 by yeast MIM complementation (PMID:40704594) and by rescue of MTCH2 loss in human cells (PMID:42308315), so the annotation stands; the note is recorded rather than acted on. Supporting Evidence: PMID:36264797 We therefore propose that MTCH1/2 are the founding members of a unique class of membrane protein insertases that exploit the SLC25 transporter fold |
| GO:0045040 protein insertion into mitochondrial outer membrane | IDA PMID:36264797 MTCH2 is a mitochondrial outer membrane protein insertase. | ACCEPT | Summary: MTCH1 participates in insertion of proteins into the mitochondrial outer membrane. Reason: Core biological process. The companion term GO:7770059 states the alpha-helical restriction explicitly and is more informative, but this term is correct as written. Supporting Evidence: PMID:42308315 we observed that MTCH1 could partially rescue loss of MTCH2 for several Ξ±-helical OM substrates |
| GO:0005515 protein binding | IPI PMID:10551805 Identification of a novel PSD-95/Dlg/ZO-1 (PDZ)-like protein... | REMOVE | Summary: Bare protein binding from the original yeast two-hybrid identification of MTCH1/PSAP as a presenilin-1 (UniProtKB:P49768) interactor. Reason: Carries no functional information. The interaction itself is retained in UniProt SUBUNIT; as a molecular function this term is uninformative. No more informative molecular function is supportable from this evidence, so the row is removed rather than rewritten. Removal does not imply the reported interaction is false. |
| GO:0005739 mitochondrion | IMP PMID:12377771 The novel presenilin-1-associated protein is a proapoptotic ... | ACCEPT | Summary: Mitochondrial localisation of PSAP/MTCH1 by fractionation and immunofluorescence. Reason: Correct. The gene also carries the more specific mitochondrial outer membrane (GO:0005741) annotation, which better describes where MTCH1 sits. Supporting Evidence: PMID:12377771 PSAP was detected in a mitochondria-enriched fraction, and PSAP immunofluorescence was present in a punctate pattern that colocalized with a mitochondrial marker. |
| GO:0009966 regulation of signal transduction | NAS PMID:10551805 Identification of a novel PSD-95/Dlg/ZO-1 (PDZ)-like protein... | REMOVE | Summary: Non-traceable author statement derived from a speculative closing sentence of the 1999 presenilin two-hybrid paper. Reason: This is not an experimental result. The paper's only basis is the speculation that followed its assignment of a PDZ-like domain to PSAP: "may participate in receptor or channel clustering and intracellular signaling events in the brain". That domain assignment has not been borne out - the current UniProt entry annotates no PDZ domain, only two SOLCAR repeats and six transmembrane helices - and MTCH1 is a multi-pass mitochondrial outer-membrane protein rather than a cytosolic scaffold. No subsequent study has assigned MTCH1 a signalling function. Removing a speculative NAS, not an experimental annotation. Supporting Evidence: PMID:10551805 These data suggest that PS-1 may associate with a PDZ-like domain-containing protein in vivo and thus may participate in receptor or channel clustering and intracellular signaling events in the brain. |
| GO:0043065 positive regulation of apoptotic process | IEP PMID:12377771 The novel presenilin-1-associated protein is a proapoptotic ... | KEEP AS NON CORE | Summary: Overexpression of PSAP/MTCH1 causes apoptosis with cytochrome c release and caspase-3 activation. Reason: A real and reproducible gain-of-function phenotype - a 2026 study had to add a pan-caspase inhibitor simply to generate MTCH1-expressing lentivirus - but it is an overexpression readout with no mechanistic link to the insertase activity, and a secondary consequence of perturbed outer-membrane protein biogenesis has not been excluded. Peripheral rather than core. The distinct MTCH2 role in BAX/BAK self-assembly (PMID:42056306) is not transferred here. Supporting Evidence: PMID:12377771 overexpression of PSAP caused apoptotic death PMID:42308315 For generating lentivirus with any MTCH1-encoding plasmids, the pan-caspase inhibitor Q-VD-OPh (MedChemExpress) was added to a final concentration of 25 ΞΌM at the time of transfection and 24 after transfection to enable lentivirus generation by preventing apoptosis. |
| GO:0045161 neuronal ion channel clustering | NAS PMID:10551805 Identification of a novel PSD-95/Dlg/ZO-1 (PDZ)-like protein... | REMOVE | Summary: Non-traceable author statement from the same speculative sentence of the 1999 paper. Reason: The only support is the phrase "may participate in receptor or channel clustering", offered as a consequence of the PDZ-like domain assignment. No PDZ domain is annotated in the current UniProt entry, no ion-channel clustering has ever been measured for MTCH1, and the protein resides in the mitochondrial outer membrane, which is not where neuronal ion channels are clustered. This is the most clearly incorrect annotation on the gene. Supporting Evidence: PMID:10551805 These data suggest that PS-1 may associate with a PDZ-like domain-containing protein in vivo and thus may participate in receptor or channel clustering and intracellular signaling events in the brain. |
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Download this section (compressed HTML)Q: MTCH1 and MTCH2 retain the SLC25 fold but no transported substrate has ever been reported for either. Is the carrier activity genuinely lost, or has it simply never been assayed? The UniProt entry still carries the "Transport" keyword and the protein name asserts a carrier function; should both be retired?
Suggested experts: Voorhees RM, Guna A
Q: Why does MTCH1, but not MTCH2, complement the yeast MIM complex even after MTCH2 is redirected to mitochondria by an MTCH1 N-terminal fusion? Is this substrate recognition, helix packing, or lipid-environment compatibility - and does it imply that MTCH1 and MTCH2 have non-identical substrate ranges in human cells?
Suggested experts: Rapaport D, Dimogkioka AR
Q: Is the apoptosis induced by MTCH1 overexpression a consequence of its insertase activity (for example mis-insertion or saturation of outer-membrane protein biogenesis), or a separate activity? Does an insertase-dead MTCH1 groove mutant still kill cells?
Suggested experts: Voorhees RM
Q: Do MTCH1 and MTCH2 have distinct physiological substrate sets, and does MTCH1 loss produce a phenotype that MTCH2 overexpression cannot rescue?
Experiment: Reconstitute purified MTCH1 into proteoliposomes and screen for transport of the standard SLC25 substrate panel (nucleotides, carboxylates, amino acids, carnitine, phosphate) under the same conditions used for canonical carriers, alongside a positive-control SLC25 carrier and the already-validated MTCH1 insertion assay as an activity control. A negative result with a demonstrably active preparation would be publishable evidence for loss of transport.
Hypothesis: MTCH1 has no transport activity and the SLC25-derived "carrier" assignment should be formally retired.
Experiment: Express wild-type MTCH1 and groove mutants (using the residue positions shown to modulate MTCH insertase activity) at matched levels, and compare insertion of a split-GFP outer-membrane reporter against cytochrome c release, caspase-3 activation and viability. Dissociation of the two readouts would establish a second, insertase-independent activity.
Hypothesis: MTCH1-induced apoptosis requires an intact insertase groove.
Experiment: Perform substrate-resolved insertion profiling (split-GFP reporters or proximity labelling across a panel of signal-anchored, tail-anchored and polytopic outer-membrane proteins) in single MTCH1 and MTCH2 knockdowns and in the double knockdown, and test cross-rescue by overexpressing each paralogue in the other's background.
Hypothesis: MTCH1 and MTCH2 act on overlapping but non-identical substrate sets.
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