mxaI encodes the small subunit (Ξ²) of the calcium-dependent methanol dehydrogenase (MxaFI-MDH), a heterotetrameric (Ξ±βΞ²β) enzyme. MxaI is a small protein of approximately 69 amino acids (~8.5 kDa) that tightly wraps around the MxaF large subunit, forming an essentially inseparable complex. While the precise function of MxaI remains unclear, it is not required for catalytic activity per se, as active MxaF enzymes lacking MxaI have been purified. MxaI likely plays structural, stability, or assembly roles rather than direct participation in catalysis. The small subunit can only efficiently associate with MxaF after PQQ incorporation, suggesting it may stabilize the properly configured active site. MxaI is unique to MxaFI-type calcium-dependent methanol dehydrogenases and is not found in XoxF-type lanthanide-dependent enzymes or other quinoproteins.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004022 alcohol dehydrogenase (NAD+) activity | IEA GO_REF:0000002 | REMOVE | Summary: Incorrect - MxaI is a non-catalytic structural subunit that does not possess enzymatic activity, and the catalytic activity resides entirely in MxaF [file:METEA/mxaI/mxaI-claude-deep-research.md, "MxaI does not directly participate in substrate binding or catalysis"]. Additionally, this InterPro-derived term is doubly wrong because the MxaFI methanol dehydrogenase is a PQQ/Ca2+-dependent quinoprotein that donates electrons to cytochrome c(L), not an NAD+-dependent alcohol dehydrogenase (UniProt EC 1.1.2.7). Falcon deep research confirms MxaI contributes structurally rather than forming the catalytic active site. |
| GO:0015945 methanol metabolic process | IEA GO_REF:0000043 | ACCEPT | Summary: Correct - MxaI is the small (beta) structural subunit of the MxaFI methanol dehydrogenase complex and therefore participates in methanol metabolism, albeit in a non-catalytic role. Falcon deep research independently confirms MxaI as the structural/auxiliary subunit required for the functional periplasmic MxaFI methanol dehydrogenase that enables the organism's canonical methanol oxidation capacity. Supporting Evidence: file:METEA/mxaI/mxaI-claude-deep-research.md this enzyme consists of the MxaF and MxaI proteins, which make up the large and small subunits of this heterotetrameric enzyme file:METEA/mxaI/mxaI-deep-research-falcon.md MxaI is the small **Ξ²** subunit of the canonical **MxaFI** methanol dehydrogenase |
| GO:0015946 methanol oxidation | IEA GO_REF:0000002 | ACCEPT | Summary: Correct - MxaI is a structural subunit of the MxaFI enzyme complex that oxidizes methanol to formaldehyde in the periplasm. Falcon deep research confirms that the MxaFI holoenzyme catalyzes the oxidation of methanol to formaldehyde, with MxaI contributing structurally rather than forming the catalytic active site itself. Supporting Evidence: file:METEA/mxaI/mxaI-claude-deep-research.md the first step in methylotrophic growth is the oxidation of methanol to formaldehyde in the periplasm by methanol dehydrogenase file:METEA/mxaI/mxaI-deep-research-falcon.md MxaI contributes structurally to this enzyme complex rather than forming the catalytic active site itself |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000043 | REMOVE | Summary: Incorrect - MxaI is a structural subunit without catalytic activity. The oxidoreductase (methanol-oxidizing) activity resides entirely in the MxaF large subunit, which carries the PQQ prosthetic group and active-site Ca2+ [file:METEA/mxaI/mxaI-claude-deep-research.md, "MxaI does not directly participate in substrate binding or catalysis"]. Falcon deep research likewise places the catalytic chemistry on the MxaFI holoenzyme via MxaF, with MxaI contributing structurally rather than forming the active site. |
| GO:0042597 periplasmic space | IEA GO_REF:0000044 | ACCEPT | Summary: Correct - MxaI is part of the MxaFI methanol dehydrogenase complex located in the periplasmic space. The UniProt record assigns a cleaved signal peptide (residues 1-22) consistent with Sec-dependent periplasmic export. Falcon deep research describes MxaI as functioning as part of a periplasm-localized MxaFI enzyme complex, although it notes that direct MxaI-specific signal-peptide/processing evidence was not located in the retrieved corpus, so periplasmic localization of MxaI is inferred from its role as a subunit of the periplasmic MxaFI complex. Supporting Evidence: file:METEA/mxaI/mxaI-deep-research-falcon.md MxaI functions as part of a periplasm-localized MxaFI enzyme complex |
| GO:0052933 alcohol dehydrogenase (cytochrome c(L)) activity | IEA GO_REF:0000120 | REMOVE | Summary: Incorrect - MxaI has no catalytic activity. The EC 1.1.2.7 cytochrome c(L)-coupled alcohol dehydrogenase activity is carried out exclusively by the MxaF large subunit, which houses the PQQ prosthetic group and active-site Ca2+ [file:METEA/mxaI/mxaI-claude-deep-research.md, "The large subunit contains the active-site residues and the PQQ prosthetic group, which is coordinated to a calcium ion in the active site"]. MxaI itself does not contribute the active site [file:METEA/mxaI/mxaI-claude-deep-research.md, "MxaI does not directly participate in substrate binding or catalysis"]. Falcon deep research independently states that MxaI contributes structurally rather than forming the catalytic active site. This activity should be retained on MxaF, not the beta subunit. |
| GO:0005198 structural molecule activity | NAS | NEW | Summary: MxaI is the small (beta) structural subunit of the MxaFI methanol dehydrogenase; it contributes to the structural integrity of the alpha2 beta2 heterotetrameric complex (GO:0005198, "The action of a molecule that contributes to the structural integrity of a complex") rather than contributing catalytic residues. Literature and local deep research both support MxaI's structural/auxiliary role, not a catalytic active-site role. Reason: PMID:21873495 describes MxaI as the small subunit of the heterotetrameric methanol dehydrogenase enzyme. Structural molecule activity is the correct molecular-function replacement for the removed catalytic MF terms inherited from InterPro/EC mapping. Supporting Evidence: PMID:21873495 In most organisms studied to date, this enzyme consists of the MxaF and MxaI proteins, which make up the large and small subunits of this heterotetrameric enzyme. file:METEA/mxaI/mxaI-claude-deep-research.md forms an integral structural component of the heterotetrameric file:METEA/mxaI/mxaI-deep-research-falcon.md MxaI contributes structurally to this enzyme complex rather than forming the catalytic active site itself |
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