| Feature | Annotation / evidence |
|---|---|
| Target identity | **mxaF / moxF**, UniProt **P16027**, locus **MexAM1_META1p4538**; encodes the large subunit of the canonical methanol dehydrogenase in *Methylorubrum extorquens* AM1. Roszczenko-Jasińska et al. explicitly map **mxaF = MexAM1_META1p4538** in AM1. (pqac-00000009) |
| Enzyme name / EC | Methanol dehydrogenase [cytochrome c] large subunit **MxaF**; part of **MxaFI-type MeDH**; EC **1.1.2.7** per UniProt target definition. Literature describes MxaFI as the classical Ca²⁺-dependent methanol dehydrogenase of Gram-negative methylotrophs. (pqac-00000006, pqac-00000017) |
| Primary reaction | Catalyzes **methanol oxidation to formaldehyde** in methylotrophy; in AM1, when lanthanides are absent, **MxaFI is the sole methanol oxidizer**. (pqac-00000006, pqac-00000009, pqac-00000013) |
| Cofactors | **PQQ-dependent** quinoprotein with **Ca²⁺** in the active site for MxaFI-type enzymes; contrasts with XoxF enzymes, which use lanthanides instead of Ca²⁺. (pqac-00000005, pqac-00000006, pqac-00000007, pqac-00000017) |
| Subunit composition | MxaFI is an **α2β2 heterotetramer** composed of large subunit **MxaF** and small subunit **MxaI**. (pqac-00000005, pqac-00000017) |
| Cellular localization | MxaFI-type MDH is a **soluble periplasmic** enzyme; methanol oxidation in AM1 occurs in the **periplasm**. (pqac-00000005, pqac-00000006, pqac-00000013) |
| Electron acceptor | The mxa operon includes **mxaG**, encoding the associated **cytochrome cL electron acceptor**; methylotrophic PQQ-ADHs in AM1 pair with cytochrome cL homologs. (pqac-00000006, pqac-00000009, pqac-00000013) |
| Operon / accessory partners | The AM1 **mxa operon** is reported as **mxaFJGIRSACKLDEHB**; associated factors include **mxaI** (small subunit), **mxaG** (cytochrome cL), **mxaJ** (periplasmic binding/chaperone-like factor), and proteins for **Ca²⁺ insertion / MxaFI maturation** (e.g., **mxaACKL**). Regulation involves **MxcQE**, **MxbDM**, and **MxaB**. (pqac-00000006, pqac-00000009) |
| Relationship to XoxF / lanthanide switch | AM1 contains one **MxaFI-type** MDH and two **XoxF-type** MDHs. In the absence of lanthanides, MxaFI supports methanol growth; in the presence of lanthanides, the **“lanthanide switch”** represses mxa genes and induces xox genes, shifting oxidation toward XoxF. XoxF1/XoxF2 also contribute to expression/regulation of the Ca²⁺-dependent MxaFI system. (pqac-00000005, pqac-00000006, pqac-00000009, pqac-00000017) |
| Promoter-reporter response to La³⁺ | In AM1 promoter fusions, **mxa** promoter signal fell from **~323 ± 63 RFU/OD600** in MeOH-only medium to **~61 ± 10** with **2 μM La³⁺**, while **xox1** rose from **~44 ± 3** to **~206 ± 11**, directly illustrating the lanthanide switch. (pqac-00000011) |
| Growth phenotypes with La³⁺ | In MeOH + La³⁺, **wild type** and **ΔmxaF** both grew at **0.16 ± 0.01 h⁻¹**; **ΔxoxF1** dropped to **0.07 ± 0.00 h⁻¹** after a **6–9 h lag**; **ΔxoxF1 ΔxoxF2** and **ΔmxaF ΔxoxF1 ΔxoxF2** grew only at **~0.04 h⁻¹** with a **6 h lag**, showing that under La³⁺ conditions XoxF, not MxaF, is the major MDH system. (pqac-00000012, pqac-00000024) |
| System-level effect of lanthanides on methanol growth | During lanthanide-dependent growth of AM1, growth on methanol is reported to be **15–22% faster** with **10–12.5% higher yield** than calcium-dependent growth, indicating more efficient Ln-supported methylotrophy overall; these gains are attributed mainly to XoxF1/ExaF rather than MxaF itself. (pqac-00000003) |
| Functional interpretation for annotation | **MxaF** is the catalytic large subunit of the **classical Ca²⁺/PQQ-dependent, periplasmic methanol dehydrogenase** that oxidizes methanol to formaldehyde and transfers electrons to **cytochrome cL (MxaG)**. It is the principal methanol oxidation system **without lanthanides**, but is transcriptionally and physiologically downshifted when **La³⁺/other lanthanides** trigger use of **XoxF**-type enzymes. (pqac-00000005, pqac-00000006, pqac-00000009, pqac-00000011, pqac-00000012) |


*Table: This table summarizes the core functional annotation for Methylorubrum extorquens AM1 mxaF/moxF (UniProt P16027), including biochemical role, localization, partners, and quantitative evidence for lanthanide-dependent regulation. It is useful as a compact evidence-backed reference for gene function and pathway context.*