Lanthanide-dependent methanol dehydrogenase (EC 1.1.2.10) that catalyzes the oxidation of methanol to formaldehyde in the periplasm. Unlike the calcium-dependent MxaFI enzyme, XoxF1 specifically requires lanthanide ions (La³⁺, Nd³⁺, Ce³⁺, Pr³⁺) as cofactors and uses pyrroloquinoline quinone (PQQ) as its prosthetic group. Forms a homodimer and transfers electrons to XoxG (cytochrome cL). Essential for lanthanide-dependent methylotrophy and is highly upregulated in the presence of lanthanides. Lanthanide ions in the active site act as Lewis acids that facilitate hydride transfer to PQQ during alcohol oxidation, and XoxF1 also contributes to the lanthanide-sensing transcriptional switch that coordinates xox and mxa operon expression.
Definition: Binding to a lanthanide (rare-earth) ion, for example La(3+), Ce(3+), Pr(3+) or Nd(3+). GO currently provides only the general parent term metal ion binding (GO:0046872), which cannot capture the lanthanide-specific cofactor requirement that distinguishes XoxF-type methanol dehydrogenases from calcium-dependent MxaFI enzymes.
Justification: XoxF1 and related XoxF-type methanol dehydrogenases specifically require lanthanides, not calcium, and a dedicated molecular function term would allow accurate annotation distinct from generic metal ion binding.
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: Correct but uninformative parent term. XoxF1 is an enzyme with well-characterized catalytic activity for methanol oxidation. This is a general root-level term subsumed by the more specific molecular function annotations (GO:0016614, GO:0052933) that should be retained as the core function. Supporting Evidence: PMID:23209751 The purified MDH had a specific activity of 10.0 U/mg of protein file:METEA/xoxF1/xoxF1-deep-research-falcon.md XoxF-type MDHs (including XoxF1) are active when Ln(III) (e.g., La(III), Ce(III), Pr(III), Nd(III)) are available and oxidize methanol → formaldehyde |
| GO:0005509 calcium ion binding | IEA GO_REF:0000120 | REMOVE | Summary: INCORRECT. XoxF1 binds LANTHANIDES (La³⁺, Nd³⁺, Ce³⁺, Pr³⁺), not calcium. When calcium is bound in the absence of lanthanides, the enzyme is inactive. This is a fundamental misannotation - likely from automated annotation that failed to recognize lanthanide specificity. XoxF1 has a diagnostic aspartate residue (Asp320) unique to lanthanide-dependent methanol dehydrogenases that is essential for lanthanide but not calcium coordination. Falcon deep research confirms XoxF purified from lanthanide-grown cells incorporated lanthanide and lacked Ca. Supporting Evidence: PMID:23209751 The purified enzyme contained 0.91 atoms of La3+ and 0.39 atoms of Ca2+ per dimer. After treatment with 50 mM EDTA, the La3+ and Ca2+ contents in the enzyme were shown to be 1.24 and 0.10 per dimer, respectively, suggesting that the La3+ is tightly bound to the enzyme PMID:32366463 XoxF1 and XoxF1 D320A, when produced in the absence of La3+, coordinated Ca2+ but exhibited little or no catalytic activity file:METEA/xoxF1/xoxF1-deep-research-falcon.md XoxF purified from lanthanide-grown cells incorporated ~1.24 atoms of La and lacked Ca |
| GO:0015945 methanol metabolic process | IEA GO_REF:0000043 | ACCEPT | Summary: CORRECT - CORE FUNCTION. XoxF1 catalyzes the first committed step in methanol metabolism by oxidizing methanol to formaldehyde. Genetic studies show deletion of both xoxF paralogs prevents methanol utilization under lanthanide-rich conditions. This is the primary biological role of the enzyme and represents essential function for lanthanide-dependent methylotrophy. Falcon deep research documents that loss of xoxF1 reduces methanol-growth performance under lanthanides and double loss of xoxF1/xoxF2 causes a stronger defect. Supporting Evidence: PMID:23209751 methanol is first oxidized to formaldehyde via methanol dehydrogenase (MDH) in the periplasm file:METEA/xoxF1/xoxF1-deep-research-falcon.md XoxF-type MDHs (including XoxF1) are active when Ln(III) (e.g., La(III), Ce(III), Pr(III), Nd(III)) are available and oxidize methanol → formaldehyde file:METEA/xoxF1/xoxF1-deep-research-falcon.md loss of either phenocopies loss of xoxF1/xoxF2 for Ln-dependent methanol growth |
| GO:0016020 membrane | IEA GO_REF:0000002 | REMOVE | Summary: INCORRECT. XoxF1 is a periplasmic protein, not membrane-bound. The N-terminal signal peptide directs the protein to the periplasm via the Sec pathway, where it is cleaved. While it may loosely associate with the membrane surface, the proper cellular component annotation is "periplasmic space" (GO:0042597), not membrane. Falcon deep research consistently describes XoxF1 as periplasmic. Supporting Evidence: PMID:23209751 XoxF1 is predicted to be a PQQ-dependent periplasmic MDH...XoxF1 may have a signal peptide for periplasmic localization file:METEA/xoxF1/xoxF1-deep-research-falcon.md AM1 xoxF1 is repeatedly described/annotated as periplasmic, consistent with the general statement that methylotrophic PQQ-ADHs are periplasmic enzymes |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: Correct but a general parent term. XoxF1 is an oxidoreductase that catalyzes the oxidation of methanol to formaldehyde, transferring electrons to XoxG (cytochrome cL). This term is subsumed by the more specific GO:0016614 and GO:0052933 which better capture the chemistry and electron acceptor; mark as non-core in favor of those. Supporting Evidence: PMID:23209751 The purified MDH had a specific activity of 10.0 U/mg of protein file:METEA/xoxF1/xoxF1-deep-research-falcon.md lanthanides in the active site act as Lewis acids that facilitate hydride transfer to PQQ during alcohol oxidation |
| GO:0016614 oxidoreductase activity, acting on CH-OH group of donors | IEA GO_REF:0000002 | ACCEPT | Summary: CORRECT - CORE FUNCTION. This is a specific molecular function term for XoxF1. The enzyme specifically oxidizes the CH-OH group of methanol (primary alcohol) to formaldehyde (aldehyde). This term accurately captures the specific chemistry of the catalytic reaction, although the even more specific GO:0052933 (alcohol dehydrogenase, cytochrome c(L) activity) best captures the electron acceptor. Supporting Evidence: PMID:23209751 methanol is first oxidized to formaldehyde via methanol dehydrogenase (MDH) file:METEA/xoxF1/xoxF1-deep-research-falcon.md are active when Ln(III) (e.g., La(III), Ce(III), Pr(III), Nd(III)) are available and oxidize methanol → formaldehyde |
| GO:0030288 outer membrane-bounded periplasmic space | IEA GO_REF:0000002 | ACCEPT | Summary: CORRECT. Accurate description of the periplasmic localization in Gram-negative bacteria. The N-terminal signal peptide (residues 1-21) directs XoxF1 to the periplasm, where it functions between the inner and outer membranes. Supporting Evidence: PMID:23209751 XoxF1 is predicted to be a PQQ-dependent periplasmic MDH file:METEA/xoxF1/xoxF1-deep-research-falcon.md A schematic model explicitly places XoxF1 in the periplasm catalyzing methanol oxidation in the presence of lanthanum |
| GO:0042597 periplasmic space | IEA GO_REF:0000044 | ACCEPT | Summary: CORRECT - PRIMARY LOCALIZATION. This is the most accurate and specific cellular component term for XoxF1. Signal peptide analysis, N-terminal sequencing of mature protein (beginning at residue 22), and immunoelectron microscopy all confirm periplasmic localization. Essential for enzyme function as methanol enters the periplasm before oxidation. Falcon deep research independently confirms periplasmic localization including a schematic model placing XoxF1 in the periplasm. Supporting Evidence: PMID:23209751 The N-terminal amino acid sequence of the MDH protein was NESVLKGVANPAEQVLQTVD, which was completely identical to 22–41 amino acid residues of the deduced amino acid sequence of the xoxF1 ORF...XoxF1 may have a signal peptide for periplasmic localization file:METEA/xoxF1/xoxF1-deep-research-falcon.md AM1 xoxF1 is repeatedly described/annotated as periplasmic, consistent with the general statement that methylotrophic PQQ-ADHs are periplasmic enzymes |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | ACCEPT | Summary: CORRECT but IMPRECISE. XoxF1 binds metal ions - specifically lanthanides (La³⁺, Nd³⁺, Ce³⁺, Pr³⁺). ICP-MS shows ~0.91-1.24 lanthanide atom per dimer. Crystal structure reveals a lanthanide coordination site with the diagnostic Asp320 residue unique to XoxF-type enzymes. This term is technically correct but not specific enough - GO currently lacks specific "lanthanide ion binding" terms. Accept as best available term, but note that a more specific lanthanide binding term should be proposed (see proposed_new_terms). Supporting Evidence: PMID:23209751 The purified enzyme contained 0.91 atoms of La3+ and 0.39 atoms of Ca2+ per dimer PMID:32366463 We report two crystal structures of XoxF1, one with and another without PQQ, both with La3+ bound in the active-site region and coordinated by Asp320 file:METEA/xoxF1/xoxF1-deep-research-falcon.md XoxF1 is a PQQ-dependent dehydrogenase whose active site requires Ln(III) rather than Ca(II), distinguishing it from Ca-dependent MxaFI |
| GO:0070968 pyrroloquinoline quinone binding | IEA GO_REF:0000117 | ACCEPT | Summary: CORRECT - ESSENTIAL COFACTOR. PQQ is the prosthetic group essential for XoxF1 catalytic activity. Crystal structure shows PQQ coordinated in the active site with multiple hydrogen bonding interactions. The PQQ quinone functionality serves as the actual redox center mediating methanol oxidation. Binds 1 PQQ per subunit (homodimer contains 2 PQQ molecules total). Falcon deep research confirms a dual requirement for PQQ and lanthanide. Supporting Evidence: PMID:23209751 XoxF1 is predicted to be a PQQ-dependent periplasmic MDH PMID:32366463 We report two crystal structures of XoxF1, one with and another without PQQ file:METEA/xoxF1/xoxF1-deep-research-falcon.md XoxF1 is a PQQ-dependent dehydrogenase whose active site requires Ln(III) rather than Ca(II), distinguishing it from Ca-dependent MxaFI |
| GO:0052933 alcohol dehydrogenase (cytochrome c(L)) activity | IDA PMID:23209751 A catalytic role of XoxF1 as La3+-dependent methanol dehydro... | NEW | Summary: NEW - CORE FUNCTION. This term is more specific than the general "oxidoreductase activity, acting on CH-OH group of donors" (GO:0016614) and accurately captures XoxF1's electron acceptor specificity. XoxF1 transfers electrons to XoxG, which is cytochrome cL. The GO definition "Catalysis of the reaction: 2 [Fe(III)cytochrome cL] + a primary alcohol = 2 [Fe(II)cytochrome cL] + an aldehyde + 2 H+" precisely describes XoxF1's mechanism - oxidizing methanol (primary alcohol) to formaldehyde (aldehyde) while reducing cytochrome cL. Supporting Evidence: PMID:23209751 XoxF1 also functions as an MDH and is La(3+)-dependent |
| GO:0042803 protein homodimerization activity | IDA PMID:23209751 A catalytic role of XoxF1 as La3+-dependent methanol dehydro... | NEW | Summary: NEW - STRUCTURAL PROPERTY. XoxF1 functions as a homodimer (α2) with a native molecular weight of ~117 kDa. Each subunit is ~61 kDa. This is in contrast to the heterotetrameric (α2β2) structure of the calcium-dependent MxaFI methanol dehydrogenase. Homodimerization appears essential for catalytic function, as both lanthanide and PQQ binding sites are present in each subunit of the functional dimer. Supporting Evidence: PMID:23209751 These results indicated that the purified MDH is a homodimer of only the α subunit...the native molecular weight of the purified protein was estimated to be ca. 117 kDa |
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Download this section (compressed HTML)Q: Does XoxF1 form a stable physical complex with XoxG (cytochrome cL) and XoxJ in the periplasm, and what is the stoichiometry of this electron-transfer assembly?
Q: To what extent does XoxF1 act as a lanthanide-sensory module influencing transcription of the mxa and xox1 operons, and is this regulatory role separable from its catalytic activity?
Experiment: Reconstitute purified XoxF1 with XoxG in vitro and measure cytochrome cL reduction kinetics across the light lanthanide series (La, Ce, Pr, Nd) to determine electron-acceptor specificity tuning.
Experiment: Use a catalytically inactive Asp320 variant in vivo to test whether XoxF1 retains its regulatory (lanthanide-switch) function independently of methanol oxidation activity.
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