| Aspect | Key points | Best supporting sources (with year, DOI/URL) |
|---|---|---|
| Identity | UniProt C5AQA2 corresponds to **mxaC** in **Methylorubrum extorquens AM1** (formerly *Methylobacterium extorquens* AM1). The gene is part of the canonical **mxa** methanol-oxidation cluster in this organism, supporting that the literature context matches the requested target rather than an unrelated homonym. (pqac-00000002) | Chistoserdova et al., 2003, *J. Bacteriol.* DOI: 10.1128/JB.185.10.2980-2987.2003, https://doi.org/10.1128/jb.185.10.2980-2987.2003 (pqac-00000002) |
| Domain/family | MxaC is annotated as a **von Willebrand factor A (VWA) domain-containing auxiliary protein**. Recent assembly work groups MxaC with **MxaS** and **MxaL** as VWA proteins that likely function together with the **MoxR-class AAA+ ATPase MxaR** in a **MoxR/VWA complex** during methanol dehydrogenase (MDH) biogenesis. (pqac-00000000, pqac-00000007) | Zhou et al., 2025, *Nat. Commun.* DOI: 10.1038/s41467-025-61958-w, https://doi.org/10.1038/s41467-025-61958-w (pqac-00000000, pqac-00000007) |
| Pathway role | MxaC functions in the **MxaFI PQQ-dependent methanol dehydrogenase maturation pathway**, not as the catalytic alcohol-oxidizing enzyme itself. It is one of the auxiliary factors required to assemble active MDH in the periplasmic methanol oxidation system. (pqac-00000001, pqac-00000002, pqac-00000004) | Zhou et al., 2025, *Nat. Commun.* DOI: 10.1038/s41467-025-61958-w, https://doi.org/10.1038/s41467-025-61958-w; Chistoserdova et al., 2003, *J. Bacteriol.* DOI: 10.1128/JB.185.10.2980-2987.2003, https://doi.org/10.1128/jb.185.10.2980-2987.2003 (pqac-00000001, pqac-00000002, pqac-00000004) |
| Mechanistic function | The strongest current mechanistic inference is that MxaC contributes to **Ca2+ incorporation into the catalytic center of MxaF** during assembly of holo-MDH. In the current assembly model, MxaC acts with **MxaR, MxaS, MxaA, MxaK, and MxaL** during the metal-loading/maturation stage. (pqac-00000000, pqac-00000004, pqac-00000007) | Zhou et al., 2025, *Nat. Commun.* DOI: 10.1038/s41467-025-61958-w, https://doi.org/10.1038/s41467-025-61958-w (pqac-00000000, pqac-00000004, pqac-00000007) |
| Experimental evidence | **Deletion of mxaC** produced **inactive MDH** with abnormal cofactor properties; **in vitro Ca2+ incubation at pH 9.5 restored the characteristic 345-nm absorption and enzymatic activity**, supporting a role in Ca2+ loading rather than direct PQQ attachment. MxaC was also among the genes required to reconstitute functional MDH in *E. coli*. (pqac-00000001) | Zhou et al., 2025, *Nat. Commun.* DOI: 10.1038/s41467-025-61958-w, https://doi.org/10.1038/s41467-025-61958-w (pqac-00000001) |
| Localization / cellular context | The relevant pathway is the **periplasmic PQQ-dependent MDH system** of Gram-negative methylotrophs. Because MxaC is an MDH auxiliary factor in the **mxa** cluster, its function is most plausibly tied to **periplasm-facing MDH biogenesis/activation**, although the provided contexts do not give a direct subcellular localization experiment specifically for MxaC. (pqac-00000001, pqac-00000004) | Zhou et al., 2025, *Nat. Commun.* DOI: 10.1038/s41467-025-61958-w, https://doi.org/10.1038/s41467-025-61958-w (pqac-00000001, pqac-00000004) |
| Recent understanding (2024) | Recent review-like synthesis places *M. extorquens* methanol metabolism at the intersection of **metal homeostasis, lanthanide biology, and MDH switching** between Ca2+-dependent MxaFI and lanthanide-dependent XoxF systems. The supplied 2024 context does **not** add MxaC-specific mechanistic details beyond this broader framework. (pqac-00000003) | Hamilton, 2024, review-like synthesis on metals/C1 metabolism; URL/DOI not available in provided context (pqac-00000003) |
| Applications / tooling context | *M. extorquens* AM1 is a recognized **C1/methanol biotechnology chassis** used for products including **mevalonate, α-humulene, 3-hydroxypropionate, and 1-butanol**. New synthetic-biology tools include repABC mini-chromosomes and inducible promoters; the native **PmxaF** promoter serves as a strong benchmark for methanol-responsive expression systems. (pqac-00000005, pqac-00000006) | Carrillo et al., 2019, *ACS Synth. Biol.* DOI: 10.1021/acssynbio.9b00220, https://doi.org/10.1021/acssynbio.9b00220 (pqac-00000005, pqac-00000006) |
| Quantitative tool data | In engineered expression systems for *M. extorquens* AM1, new inducible promoters spanned **6–36-fold induction**; PA1/PL-derived promoters ranged from **9% to 166% of PmxaF** activity, whereas a previous inducible promoter reached only **33% of PmxaF**. These values are useful when contextualizing the *mxa* system for practical engineering. (pqac-00000006) | Carrillo et al., 2019, *ACS Synth. Biol.* DOI: 10.1021/acssynbio.9b00220, https://doi.org/10.1021/acssynbio.9b00220 (pqac-00000006) |
| Evidence type / confidence | Confidence is **moderate for pathway assignment and metal-loading role** because recent primary data link mxaC deletion to inactive MDH rescued by Ca2+ and place MxaC in the auxiliary assembly machinery; confidence is **lower for direct biochemical activity or exact localization**, as the supplied evidence does not show purified MxaC activity or a direct localization assay. (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000003) | Zhou et al., 2025; Chistoserdova et al., 2003; Hamilton, 2024 review-like context (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000003) |


*Table: This table summarizes the best-supported functional annotation for MxaC (UniProt C5AQA2) in Methylorubrum extorquens AM1 using only the provided evidence contexts. It highlights identity verification, VWA/MoxR-related assembly role, experimental support for Ca2+-dependent MDH maturation, and biotechnology context for the host organism.*