mxaJ

Summary: KEEP_AS_NON_CORE. MxaJ is required for biogenesis of active methanol dehydrogenase and is a co-regulated component of the methanol-oxidation (mxa) system, so participation in methanol metabolism is well supported, but this broad term is subsumed by the more specific methanol catabolic process (GO:0046170) used as the core process term.

Reason: Recent structural work establishes MxaJ as an MDH assembly chaperone that promotes PQQ incorporation into the catalytic MxaF subunit, placing it firmly within methanol metabolism. This broader term is correct but less informative than methanol catabolic process (GO:0046170), which is the more specific catabolism term and is retained as the core process; GO:0015945 is therefore kept as non-core.

Summary: ACCEPT. MxaJ is an exported precursor protein that functions in the periplasm, where PQQ-dependent MDH assembles.

Reason: Periplasmic localization is supported by the UniProt signal peptide and SUBCELLULAR LOCATION annotation and by literature describing mxaJ as encoding a periplasmic precursor. The export pathway (Tat vs Sec) is not experimentally resolved for AM1 MxaJ.

Summary: ACCEPT. This is the most specific applicable process term: MxaJ enables catabolism of methanol by maturing the periplasmic MDH that performs the first oxidation step.

Reason: MxaJ is an accessory factor in the periplasmic methanol oxidation module; its chaperone role in producing active MxaFI directly supports methanol catabolism. This term is preferred over the broader GO:0015945.

Summary: NEW (best-available MF; imperfect fit). Replaces the uninformative root term binding (GO:0005488) with a chaperone-class molecular function. MxaJ is an assembly/maturation chaperone: it binds the ALREADY-FOLDED MxaF client and promotes PQQ-cofactor incorporation during MDH maturation. It does NOT fold MxaF, so GO:0044183 is used only as the closest existing MF term pending a more precise one.

Reason: Generic binding (GO:0005488) provides no functional information. Zhou et al. 2025 show that MxaJ binds the folded catalytic subunit MxaF, forms an MxaF/MxaJ intermediate, and promotes incorporation of the PQQ cofactor, then is released upon MxaI engagement. IMPORTANT CAVEAT: GO:0044183 (protein folding chaperone) is an IMPERFECT fit. Its definition and curator note specify a chaperone that "binds an unfolded protein to fold it"; MxaJ instead acts on the already-folded MxaF and is an ASSEMBLY/MATURATION (cofactor-incorporation) chaperone, not a folding chaperone. An OLS survey of MF chaperone terms found no better existing term: metallochaperone activity (GO:0016530) is restricted to metal-ion delivery (PQQ is an organic cofactor, not a metal), unfolded protein holdase activity (GO:0140309) requires an unfolded client, and no generic "assembly chaperone" or "cofactor-incorporation chaperone" MF term exists. GO:0044183 is therefore retained as the best available chaperone-class MF descriptor pending a more precise term; the assembly process itself is captured by chaperone-mediated protein complex assembly (GO:0051131). This MF should be revisited if/when a more specific assembly/maturation chaperone MF term is added to GO.

Summary: NEW. Captures the biological process MxaJ performs: it chaperones assembly of the mature MxaF/MxaI methanol dehydrogenase complex by promoting PQQ incorporation, then is released and is not part of the finished complex.

Reason: Zhou et al. 2025 show MxaJ binds MxaF, promotes PQQ entry, and is displaced upon MxaI engagement to yield mature PQQ-loaded MxaF/MxaI. This matches the definition of chaperone-mediated protein complex assembly (assembly mediated by chaperone molecules that do not form part of the finished complex) and is more mechanistically precise than the broad methanol-metabolism process terms alone.