mxaG

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005506 iron ion binding	IEA GO_REF:0000002	ACCEPT	Summary: Correct - MxaG binds iron in the heme prosthetic group [file:METEA/mxaG/mxaG-uniprot.txt, "Binds 1 heme c group covalently per subunit" and "Iron" in keywords]. The UniProt feature table specifies the axial iron-coordinating histidine (residue 94, ligand Fe), consistent with iron ion binding in a c-type cytochrome heme. Reason: The heme c iron is the redox-active center of cytochrome c_L; iron ion binding is a correct molecular function supported by the UniProt covalent heme c binding sites and the Fe axial-binding residue.
GO:0009055 electron transfer activity	IEA GO_REF:0000002	ACCEPT	Summary: Correct and core - MxaG (cytochrome c_L) functions as the dedicated electron acceptor for periplasmic PQQ-dependent methanol dehydrogenase, accepting electrons from reduced MxaFI and transferring them onward to additional cytochromes in the respiratory electron transport chain [file:METEA/mxaG/mxaG-uniprot.txt, "Electron acceptor for MDH. Acts in methanol oxidation"]. Reason: This is the primary molecular function of the gene product. Multiple authoritative sources name MxaG as the cytochrome c_L electron-transfer partner of methanol dehydrogenase, transferring electrons from PQQ to downstream cytochromes. Supporting Evidence: file:METEA/mxaG/mxaG-deep-research-falcon.md All methylotrophic PQQ-ADHs are periplasmic enzymes associated with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons from PQQ to additional cytochromes in the electron transport chain file:METEA/mxaG/mxaG-deep-research-falcon.md the specific cytochrome c that accepts electrons from methanol dehydrogenase file:METEA/mxaG/mxaG-deep-research-falcon.md reduced PQQ is reoxidized by transferring electrons to the heme of cytochrome cL, which is then oxidized by downstream cytochromes
GO:0015945 methanol metabolic process	IEA GO_REF:0000043	ACCEPT	Summary: Correct and core - MxaG participates in methanol metabolism as the electron acceptor in the calcium-dependent methanol oxidation pathway, feeding electrons from periplasmic methanol oxidation into respiration [file:METEA/mxaG/mxaG-uniprot.txt, "Acts in methanol oxidation" and "Methanol utilization" in keywords]. Reason: MxaG is genetically part of the mxa methanol dehydrogenase cluster and functionally required for methanol oxidation by accepting electrons from the MDH PQQ cofactor; the deep research confirms its role in the periplasmic methanol-oxidation electron-transfer module. Supporting Evidence: file:METEA/mxaG/mxaG-deep-research-falcon.md methanol oxidation occurs in the periplasm via PQQ-dependent ADHs file:METEA/mxaG/mxaG-deep-research-falcon.md Electrons are transferred from PQQ to cytochrome cL and then to additional cytochromes/respiratory chain components, coupling methanol oxidation to energy generation
GO:0020037 heme binding	IEA GO_REF:0000002	ACCEPT	Summary: Correct - MxaG contains one heme c group covalently bound per subunit [file:METEA/mxaG/mxaG-uniprot.txt, "Binds 1 heme c group covalently per subunit"]. The covalent heme c is the redox cofactor through which MxaG accepts and donates electrons. Reason: Covalent heme c binding is documented in UniProt (CXXCH-type c-type cytochrome with covalent thioether attachment at residues 90 and 93 and Fe axial coordination at residue 94); the heme is essential to its electron-transfer function.
GO:0042597 periplasmic space	IEA GO_REF:0000120	ACCEPT	Summary: Correct and core - MxaG is localized to the periplasm where it accepts electrons from periplasmic MxaFI [file:METEA/mxaG/mxaG-uniprot.txt, "SUBCELLULAR LOCATION: Periplasm"]. It bears an N-terminal signal peptide (residues 1-25) consistent with periplasmic export. Reason: UniProt assigns periplasmic localization and a cleaved signal peptide; the deep research independently places cytochrome c_L in the periplasmic methanol-oxidation electron-transfer chain alongside the periplasmic PQQ-dependent dehydrogenases. Supporting Evidence: file:METEA/mxaG/mxaG-deep-research-falcon.md All methylotrophic PQQ-ADHs are periplasmic enzymes associated with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons from PQQ to additional cytochromes in the electron transport chain
GO:0046872 metal ion binding	IEA GO_REF:0000043	KEEP AS NON CORE	Summary: Correct but general - MxaG binds iron in the heme group. The more specific terms GO:0005506 (iron ion binding) and GO:0020037 (heme binding) better capture this function. Reason: This is a redundant generic parent of the iron ion binding annotation already present; it is retained as non-core because the specific iron ion binding and heme binding terms convey the actual molecular context.

Core Functions

MxaG functions as the dedicated electron acceptor (cytochrome c_L) for the calcium-dependent methanol dehydrogenase MxaFI system. The c-type cytochrome accepts electrons from reduced MxaFI following methanol oxidation to formaldehyde, transferring them via its covalent heme c to downstream respiratory chain components. MxaG itself does not catalyze methanol oxidation; rather, it mediates electron transfer from the MDH redox cofactor PQQ to additional periplasmic cytochromes. MxaG exhibits a redox potential of +256 mV at pH 7.0, which is optimized for efficient electron transfer from the calcium-dependent methanol dehydrogenase system. This is notably higher than the +172 mV potential of XoxG, the analogous cytochrome serving the lanthanide-dependent XoxF system, reflecting the different biochemical properties of the two methanol oxidation pathways.

Molecular Function:

electron transfer activity

Directly Involved In:

methanol metabolic process

Cellular Locations:

periplasmic space

Supporting Evidence:

file:METEA/mxaG/mxaG-uniprot.txt
Electron acceptor for MDH. Acts in methanol oxidation...Redox potential: E(0) is about +256 mV... SUBCELLULAR LOCATION: Periplasm...Binds 1 heme c group covalently per subunit
file:METEA/mxaG/mxaG-deep-research-falcon.md
All methylotrophic PQQ-ADHs are periplasmic enzymes associated with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons from PQQ to additional cytochromes in the electron transport chain
file:METEA/mxaG/mxaG-deep-research-falcon.md
MxaG itself does not catalyze methanol oxidation; rather, it

References

file:METEA/mxaG/mxaG-uniprot.txt

UniProt entry for mxaG cytochrome c_L

file:METEA/mxaG/mxaG-deep-research-falcon.md

Falcon deep research report for mxaG (cytochrome c_L) in Methylorubrum extorquens AM1

MxaG (cytochrome c_L) is the cognate periplasmic electron acceptor for methylotrophic PQQ-dependent methanol/alcohol dehydrogenases, transferring electrons from PQQ to additional cytochromes in the respiratory electron transport chain.

"All methylotrophic PQQ-ADHs are periplasmic enzymes associated with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons from PQQ to additional cytochromes in the electron transport chain"
The mxa methanol-oxidation gene cluster encodes the specific cytochrome c that accepts electrons from methanol dehydrogenase.

"the specific cytochrome c that accepts electrons from methanol dehydrogenase"
Mechanistically, reduced PQQ is reoxidized by transferring electrons to the heme of cytochrome c_L, which is in turn oxidized by downstream cytochromes.

"reduced PQQ is reoxidized by transferring electrons to the heme of cytochrome cL, which is then oxidized by downstream cytochromes"
MxaG is a shuttle, not a catalyst - it does not itself catalyze methanol oxidation but mediates electron transfer from the MDH redox cofactor PQQ to downstream respiratory components.

"MxaG itself does not catalyze methanol oxidation; rather, it"
Methanol oxidation by the PQQ-dependent dehydrogenases, and hence the cytochrome c_L electron-transfer step it feeds, occurs in the periplasm.

"methanol oxidation occurs in the periplasm via PQQ-dependent ADHs"
Electron flow proceeds from PQQ to cytochrome c_L and onward to additional cytochromes/respiratory chain components, coupling methanol oxidation to energy generation.

"Electrons are transferred from PQQ to cytochrome cL and then to additional cytochromes/respiratory chain components, coupling methanol oxidation to energy generation"

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms.

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods.

Deep Research

Falcon

(mxaG-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 15 citations 2 artifacts 2026-06-03T09:33:11.772722

Edison artifact artifact-00 (text/markdown)

## Context ID: pqac-00000006 The document contains a schematic representation of methanol oxidation in the periplasm in Figure 1 on page 5. This figure shows me (image/png)

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research report: moxG / mxaG (UniProt P14774) in Methylorubrum extorquens AM1

0) Target verification (critical identity check)

User-specified target: UniProt P14774, described as Cytochrome c-L (precursor), gene moxG with synonym mxaG, in Methylorubrum extorquens strain AM1.

Verification from retrieved literature:
- In Methylorubrum extorquens AM1, the canonical methanol oxidation gene cluster includes mxaG within the operon mxaFJGIRSACKLDEHB (a 12.5-kb cluster) (publication date: May 2003) (https://doi.org/10.1128/jb.185.10.2980-2987.2003). This anchors mxaG in the correct organism and pathway context (chistoserdova2003methylotrophyinmethylobacterium pages 4-5).
- The same 2003 genomic analysis explicitly lists mxaG (also noted as moxG) and annotates it as a cytochrome c-type protein (Table 1 in that work) (publication date: May 2003) (https://doi.org/10.1128/jb.185.10.2980-2987.2003) (chistoserdova2003methylotrophyinmethylobacterium pages 2-3).
- Multiple sources explicitly identify MxaG as cytochrome cL, the cognate electron acceptor for periplasmic PQQ-dependent methanol dehydrogenases (MDH/PQQ-ADHs) in Methylorubrum extorquens AM1 or its historical name (Methylobacterium extorquens) (roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4, purves2019understandingtheimpacts pages 24-28).

Limitations of the retrieved corpus: the full UniProt accession P14774 is not explicitly mentioned in the retrieved papers; thus the accession-level mapping is not directly evidenced here, but the gene-symbol crosswalk mxaG ↔ moxG in M. extorquens AM1 is supported (chistoserdova2003methylotrophyinmethylobacterium pages 2-3).

1) Key concepts and definitions (current understanding)

1.1 What is cytochrome cL (MxaG/MoxG)?

Cytochrome cL is a c-type cytochrome that functions as the physiological electron acceptor for periplasmic, PQQ-dependent alcohol/methanol dehydrogenases used in methylotrophy (roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4, purves2019understandingtheimpacts pages 24-28). In Methylorubrum extorquens AM1, MxaG is specifically named as the cytochrome cL partner associated with methylotrophic PQQ-ADHs (roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4).

1.2 PQQ-dependent methanol oxidation and electron transfer

In periplasmic methanol oxidation, methanol dehydrogenase (MDH) oxidizes methanol to formaldehyde and reduces the prosthetic group PQQ. The reduced PQQ is then reoxidized by transferring electrons to the heme of cytochrome cL, which passes electrons further into the electron transport chain (roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4, rojas2021elucidationofthe pages 19-23, rojas2021elucidationofthea pages 19-23).

1.3 “MOX/mxa” gene cluster and operon organization

A foundational genomic analysis of M. extorquens AM1 describes a 12.5-kb cluster containing 14 mxa genes (mxaFJGIRSACKLDEHB) transcribed in the same direction; these genes encode methanol dehydrogenase structural polypeptides and the specific cytochrome c that accepts electrons from methanol dehydrogenase, along with other essential methanol oxidation proteins (https://doi.org/10.1128/jb.185.10.2980-2987.2003; publication date May 2003) (chistoserdova2003methylotrophyinmethylobacterium pages 4-5).

2) Functional annotation of moxG/mxaG: molecular function, pathway role, and localization

2.1 Primary molecular function

Best-supported function: moxG/mxaG encodes cytochrome cL (MxaG), which accepts electrons derived from MDH/PQQ chemistry and transfers them onward to additional cytochromes in the electron transport chain.

Evidence:
- “All methylotrophic PQQ-ADHs are periplasmic enzymes associated with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons from PQQ to additional cytochromes in the electron transport chain.” (publication date Jul 2020, Scientific Reports, https://doi.org/10.1038/s41598-020-69401-4) (roszczenkojasinska2020geneproductsand pages 1-4).
- The AM1 genome analysis states that the 14-gene mxa cluster encodes MDH structural polypeptides and “the specific cytochrome c that accepts electrons from methanol dehydrogenase” (publication date May 2003, Journal of Bacteriology, https://doi.org/10.1128/jb.185.10.2980-2987.2003) (chistoserdova2003methylotrophyinmethylobacterium pages 4-5).
- Mechanistically, reduced PQQ is reoxidized by transferring electrons to the heme of cytochrome cL, which is then oxidized by downstream cytochromes (rojas2021elucidationofthe pages 19-23, rojas2021elucidationofthea pages 19-23).

Reaction context (what MxaG enables rather than catalyzes): MxaG itself does not catalyze methanol oxidation; rather, it mediates electron transfer from the MDH redox cofactor (PQQ) to downstream respiratory components (roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4, rojas2021elucidationofthe pages 19-23, rojas2021elucidationofthea pages 19-23).

2.2 Biological process and pathway placement

moxG/mxaG is part of aerobic methylotrophic methanol utilization, specifically the periplasmic methanol-oxidation module that feeds electrons into respiration.

Methanol oxidation is described as occurring in the periplasm via PQQ-dependent ADHs in M. extorquens AM1, and these enzymes are associated with cytochrome cL (roszczenkojasinska2020geneproductsand pages 1-4).
Electrons are transferred from PQQ to cytochrome cL and then to additional cytochromes/respiratory chain components, coupling methanol oxidation to energy generation (roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4, rojas2021elucidationofthe pages 19-23, rojas2021elucidationofthea pages 19-23).

2.3 Subcellular localization

The strongest localization inference supported by the retrieved evidence is periplasmic association:
- Methylotrophic PQQ-ADHs are explicitly described as periplasmic and associated with cytochrome cL (roszczenkojasinska2020geneproductsand pages 1-4). This supports that cytochrome cL (MxaG) functions in the periplasmic electron-transfer chain (roszczenkojasinska2020geneproductsand pages 1-4).
- A schematic figure from Roszczenko-Jasińska et al. depicts methanol oxidation in the periplasm by MxaFI and XoxF enzymes (Figure 1; publication date Jul 2020, https://doi.org/10.1038/s41598-020-69401-4) (roszczenkojasinska2020geneproductsand media 5e588001).

3) Recent developments and latest research (emphasis 2023–2024)

3.1 2023: rare-earth element (REE/lanthanide) “switch” and relationship to cytochrome partners

A 2023 review focused on rare earth element utilization summarizes the division of labor between Ca-dependent MxaFI MDH systems and lanthanide-dependent XoxF MDH systems and explicitly places mxaG as encoding the cognate physiological electron acceptor (cytochrome cL) for methanol oxidation (xie2023molecularmechanismsof pages 13-18). It also describes a widely reported regulatory phenomenon: in the presence of lanthanides, expression of MxaF-type systems is suppressed while XoxF-type systems are induced (xie2023molecularmechanismsof pages 13-18).

Interpretation for moxG/mxaG: in organisms/conditions where the XoxF system dominates, cytochrome XoxG (a cytochrome cL analog) may be the primary periplasmic electron acceptor for lanthanide-dependent MDH, while MxaG remains the canonical partner for the Ca-dependent MxaFI MDH (roszczenkojasinska2020geneproductsand pages 1-4, xie2023molecularmechanismsof pages 13-18).

3.2 2024: ecosystem-scale framing of lanthanide methylotrophy (limited mxaG-specific detail)

Although a 2024 source was retrieved related to widespread bacterial use of lanthanides, the accessible evidence in this run did not provide mxaG-specific mechanistic or quantitative updates suitable for citation about MxaG itself.

4) Current applications and real-world implementations

4.1 Engineering and “C1-bioeconomy” context

The methylotroph Methylorubrum extorquens AM1 is repeatedly framed in the literature as a platform organism for methanol-based biotechnology. In this context, methanol oxidation (and therefore functional electron transfer via cytochrome partners such as MxaG) is central to growth and productivity on methanol (purves2019understandingtheimpacts pages 24-28). While this run’s strongest application-specific citation is general rather than mechanistically focused, it supports that AM1 has been used for bioproduction in applied settings (purves2019understandingtheimpacts pages 24-28).

4.2 Metal/lanthanide-relevant applications (contextual)

A major applied motivation discussed for M. extorquens AM1 is the capacity of methylotrophs to sense/transport lanthanides, with potential relevance to sustainable recovery of lanthanides; however, this run’s strongest lanthanide-focused evidence addresses transport/storage and XoxF function more than MxaG itself (roszczenkojasinska2020geneproductsand pages 1-4).

5) Expert opinions / authoritative synthesis from high-citation sources

Chistoserdova et al. (2003, Journal of Bacteriology) provides a highly cited genomic synthesis of methylotrophy modules in AM1, emphasizing that the mxa cluster encodes MDH structural polypeptides and the specific cytochrome c electron acceptor, supporting the canonical view of mxaG/moxG as part of the methanol oxidation module (https://doi.org/10.1128/jb.185.10.2980-2987.2003; publication date May 2003) (chistoserdova2003methylotrophyinmethylobacterium pages 4-5).
Roszczenko-Jasińska et al. (2020, Scientific Reports) provides an authoritative summary for AM1 that explicitly identifies cytochrome cL partners (MxaG/XoxG/ExaG) and their role transferring electrons from PQQ to the electron transport chain, reinforcing the accepted functional definition (https://doi.org/10.1038/s41598-020-69401-4; publication date Jul 2020) (roszczenkojasinska2020geneproductsand pages 1-4).

6) Statistics and data points from retrieved studies (recent where possible)

The retrieved corpus contained limited directly mxaG-specific quantitative biochemistry (e.g., redox potentials, kcat/KM) suitable for extraction. However, two quantitative/structured datapoints relevant to confidence in methylotrophy network assignment include:
- In a transposon mutagenesis study in AM1 focused on lanthanide-dependent methanol metabolism, the authors screened >600 transposon mutants and followed up genes identified independently four or more times (28 genes), with some mutants showing ≥30% reductions in growth rate; this supports the utility of genetic approaches in mapping methanol oxidation accessory functions, though it is not a direct measurement of MxaG activity (roszczenkojasinska2020geneproductsand pages 5-6).
- The 2003 genomic work defines the mxa cluster size (12.5 kb) and gene count (14 mxa genes) as a structured genomic feature of the AM1 methanol oxidation module (chistoserdova2003methylotrophyinmethylobacterium pages 4-5).

7) Summary of supported annotation (concise)

Gene / protein: moxG (syn. mxaG) encodes cytochrome cL in Methylorubrum extorquens AM1 (roszczenkojasinska2020geneproductsand pages 1-4, purves2019understandingtheimpacts pages 24-28, chistoserdova2003methylotrophyinmethylobacterium pages 2-3).
Primary role: electron acceptor/shuttle for methanol oxidation via PQQ-dependent MDH/PQQ-ADHs; transfers electrons onward to additional cytochromes/respiration (roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4, rojas2021elucidationofthe pages 19-23, rojas2021elucidationofthea pages 19-23).
Localization: functionally associated with periplasmic methanol oxidation enzyme systems (roszczenkojasinska2020geneproductsand pages 1-4, roszczenkojasinska2020geneproductsand media 5e588001).
Genomic context: part of the mxa operon (mxaFJGIRSACKLDEHB) that encodes MDH components and the specific cytochrome c electron acceptor (chistoserdova2003methylotrophyinmethylobacterium pages 4-5).

Evidence map

Claim (function/localization/pathway)	Evidence summary	Organism/strain context	Source (with year, journal, URL)	Citation id
mxaG encodes cytochrome cL, the cognate electron acceptor associated with methanol dehydrogenase	Review text explicitly states that methylotrophic PQQ-dependent alcohol dehydrogenases are associated with cytochrome cL and names MxaG as the cytochrome cL partner; another source states that mxaG encodes cytochrome cL and identifies it as the primary electron acceptor in the MDH system.	Methylorubrum extorquens AM1 / historical Methylobacterium extorquens context	Roszczenko-Jasińska et al., 2020, Scientific Reports, https://doi.org/10.1038/s41598-020-69401-4; Purves, 2019, unknown journal, URL not available in retrieved record	(roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4, purves2019understandingtheimpacts pages 24-28)
Cytochrome cL functions in the periplasmic methanol-oxidation electron transfer chain	Evidence states methanol oxidation occurs in the periplasm via PQQ-dependent ADHs/MDH, and that the associated cytochrome cL transfers electrons from reduced PQQ to additional cytochromes in the electron transport chain.	Methylorubrum extorquens AM1	Roszczenko-Jasińska et al., 2020, Scientific Reports, https://doi.org/10.1038/s41598-020-69401-4	(roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4)
In Methylobacterium/Methylorubrum extorquens, mxaG is genetically part of the mxa methanol dehydrogenase cluster	The mxa operon is described as mxaFJGIRSACKLDEHB, placing mxaG within the canonical methanol dehydrogenase gene cluster and supporting its dedicated role in MDH function.	Methylorubrum extorquens AM1	Roszczenko-Jasińska et al., 2020, Scientific Reports, https://doi.org/10.1038/s41598-020-69401-4	(roszczenkojasinska2020geneproductsand pages 4-5)
Electron flow proceeds from MDH-reduced PQQ to cytochrome cL	A source describes that methanol oxidation by periplasmic MDH reduces PQQ, and the reduced PQQ is then reoxidized by transfer of two electrons to the heme of cytochrome cL.	Historical naming: Methylobacterium extorquens (same species complex as Methylorubrum extorquens)	Rojas, 2021, unknown journal, URL not available in retrieved record	(rojas2021elucidationofthe pages 19-23, rojas2021elucidationofthea pages 19-23)
Cytochrome cL passes electrons onward to downstream cytochromes/respiratory components	One source states cytochrome cL transfers electrons from PQQ to additional cytochromes in the electron transport chain; another states cytochrome cL is oxidized by cytochrome cH, linking methanol oxidation to respiration and energy conservation.	Methylorubrum extorquens AM1 / historical Methylobacterium extorquens context	Roszczenko-Jasińska et al., 2020, Scientific Reports, https://doi.org/10.1038/s41598-020-69401-4; Rojas, 2021, unknown journal, URL not available in retrieved record	(roszczenkojasinska2020geneproductsand pages 4-5, rojas2021elucidationofthe pages 19-23, rojas2021elucidationofthea pages 19-23)
Methanol oxidation enzymes and their cytochrome cL partner are localized in the periplasm	The evidence states that methylotrophic PQQ-ADHs are periplasmic and associated with cytochrome cL; a figure-based summary also depicts methanol oxidation in the periplasm by MxaFI/XoxF enzymes.	Methylorubrum extorquens AM1	Roszczenko-Jasińska et al., 2020, Scientific Reports, https://doi.org/10.1038/s41598-020-69401-4	(roszczenkojasinska2020geneproductsand pages 1-4, roszczenkojasinska2020geneproductsand media 5e588001)
The gathered literature supports mxaG as the relevant symbol; explicit use of the synonym moxG was not found in the retrieved evidence	Across the directly gathered evidence, the gene is referred to as mxaG encoding cytochrome cL; the retrieved texts did not explicitly mention the synonym moxG or UniProt P14774.	Methylorubrum extorquens AM1 / historical Methylobacterium extorquens context	Roszczenko-Jasińska et al., 2020, Scientific Reports, https://doi.org/10.1038/s41598-020-69401-4; Rojas, 2021, unknown journal, URL not available in retrieved record; Purves, 2019, unknown journal, URL not available in retrieved record	(roszczenkojasinska2020geneproductsand pages 4-5, roszczenkojasinska2020geneproductsand pages 1-4, rojas2021elucidationofthe pages 19-23, rojas2021elucidationofthea pages 19-23, purves2019understandingtheimpacts pages 24-28)

Table: This table summarizes directly supported functional annotation claims for Methylorubrum extorquens AM1 moxG/mxaG (cytochrome cL), including function, localization, and pathway role. It is useful as a traceable evidence map restricted to the gathered sources and context IDs.

References

(chistoserdova2003methylotrophyinmethylobacterium pages 4-5): Ludmila Chistoserdova, Sung-Wei Chen, Alla Lapidus, and Mary E. Lidstrom. Methylotrophy in methylobacterium extorquens am1 from a genomic point of view. Journal of Bacteriology, 185:2980-2987, May 2003. URL: https://doi.org/10.1128/jb.185.10.2980-2987.2003, doi:10.1128/jb.185.10.2980-2987.2003. This article has 402 citations and is from a peer-reviewed journal.
(chistoserdova2003methylotrophyinmethylobacterium pages 2-3): Ludmila Chistoserdova, Sung-Wei Chen, Alla Lapidus, and Mary E. Lidstrom. Methylotrophy in methylobacterium extorquens am1 from a genomic point of view. Journal of Bacteriology, 185:2980-2987, May 2003. URL: https://doi.org/10.1128/jb.185.10.2980-2987.2003, doi:10.1128/jb.185.10.2980-2987.2003. This article has 402 citations and is from a peer-reviewed journal.
(roszczenkojasinska2020geneproductsand pages 4-5): Paula Roszczenko-Jasińska, Huong N. Vu, Gabriel A. Subuyuj, Ralph Valentine Crisostomo, James Cai, Nicholas F. Lien, Erik J. Clippard, Elena M. Ayala, Richard T. Ngo, Fauna Yarza, Justin P. Wingett, Charumathi Raghuraman, Caitlin A. Hoeber, Norma C. Martinez-Gomez, and Elizabeth Skovran. Gene products and processes contributing to lanthanide homeostasis and methanol metabolism in methylorubrum extorquens am1. Scientific Reports, Jul 2020. URL: https://doi.org/10.1038/s41598-020-69401-4, doi:10.1038/s41598-020-69401-4. This article has 98 citations and is from a peer-reviewed journal.
(roszczenkojasinska2020geneproductsand pages 1-4): Paula Roszczenko-Jasińska, Huong N. Vu, Gabriel A. Subuyuj, Ralph Valentine Crisostomo, James Cai, Nicholas F. Lien, Erik J. Clippard, Elena M. Ayala, Richard T. Ngo, Fauna Yarza, Justin P. Wingett, Charumathi Raghuraman, Caitlin A. Hoeber, Norma C. Martinez-Gomez, and Elizabeth Skovran. Gene products and processes contributing to lanthanide homeostasis and methanol metabolism in methylorubrum extorquens am1. Scientific Reports, Jul 2020. URL: https://doi.org/10.1038/s41598-020-69401-4, doi:10.1038/s41598-020-69401-4. This article has 98 citations and is from a peer-reviewed journal.
(purves2019understandingtheimpacts pages 24-28): K Purves. Understanding the impacts of viruses on microbial methanol utilisation in seawater. Unknown journal, 2019.
(rojas2021elucidationofthe pages 19-23): J Rojas. Elucidation of the plant growth–promoting effect of hartmannibacter diazotrophicus on tolerance of barley to salt stress. Unknown journal, 2021.
(rojas2021elucidationofthea pages 19-23): J Rojas. Elucidation of the plant growth–promoting effect of hartmannibacter diazotrophicus on tolerance of barley to salt stress. Unknown journal, 2021.
(roszczenkojasinska2020geneproductsand media 5e588001): Paula Roszczenko-Jasińska, Huong N. Vu, Gabriel A. Subuyuj, Ralph Valentine Crisostomo, James Cai, Nicholas F. Lien, Erik J. Clippard, Elena M. Ayala, Richard T. Ngo, Fauna Yarza, Justin P. Wingett, Charumathi Raghuraman, Caitlin A. Hoeber, Norma C. Martinez-Gomez, and Elizabeth Skovran. Gene products and processes contributing to lanthanide homeostasis and methanol metabolism in methylorubrum extorquens am1. Scientific Reports, Jul 2020. URL: https://doi.org/10.1038/s41598-020-69401-4, doi:10.1038/s41598-020-69401-4. This article has 98 citations and is from a peer-reviewed journal.
(xie2023molecularmechanismsof pages 13-18): R Xie. Molecular mechanisms of rare earth element utilization by methane-oxidizing bacteria and protease-producing bacteria. Unknown journal, 2023.
(roszczenkojasinska2020geneproductsand pages 5-6): Paula Roszczenko-Jasińska, Huong N. Vu, Gabriel A. Subuyuj, Ralph Valentine Crisostomo, James Cai, Nicholas F. Lien, Erik J. Clippard, Elena M. Ayala, Richard T. Ngo, Fauna Yarza, Justin P. Wingett, Charumathi Raghuraman, Caitlin A. Hoeber, Norma C. Martinez-Gomez, and Elizabeth Skovran. Gene products and processes contributing to lanthanide homeostasis and methanol metabolism in methylorubrum extorquens am1. Scientific Reports, Jul 2020. URL: https://doi.org/10.1038/s41598-020-69401-4, doi:10.1038/s41598-020-69401-4. This article has 98 citations and is from a peer-reviewed journal.

Artifacts

Edison artifact artifact-00

Citations

chistoserdova2003methylotrophyinmethylobacterium pages 4-5
chistoserdova2003methylotrophyinmethylobacterium pages 2-3
roszczenkojasinska2020geneproductsand pages 1-4
xie2023molecularmechanismsof pages 13-18
purves2019understandingtheimpacts pages 24-28
roszczenkojasinska2020geneproductsand pages 5-6
roszczenkojasinska2020geneproductsand pages 4-5
rojas2021elucidationofthe pages 19-23
rojas2021elucidationofthea pages 19-23
https://doi.org/10.1128/jb.185.10.2980-2987.2003
https://doi.org/10.1128/jb.185.10.2980-2987.2003;
https://doi.org/10.1038/s41598-020-69401-4
https://doi.org/10.1038/s41598-020-69401-4;
https://doi.org/10.1128/jb.185.10.2980-2987.2003,
https://doi.org/10.1038/s41598-020-69401-4,

📄 View Raw YAML

id: P14774
gene_symbol: mxaG
product_type: PROTEIN
taxon:
  id: NCBITaxon:272630
  label: Methylorubrum extorquens AM1
description: 'mxaG (also known as moxG) encodes cytochrome c_L, a specialized c-type
  cytochrome that serves as the dedicated electron acceptor for the calcium-dependent
  methanol dehydrogenase MxaFI. The protein contains heme c covalently attached and
  exhibits a redox potential of +256 mV at pH 7.0, substantially higher than the analogous
  XoxG cytochrome (+172 mV) that serves the lanthanide-dependent XoxF system. Located
  in the periplasm, MxaG accepts electrons from reduced MxaFI following methanol oxidation
  and transfers them to downstream components of the respiratory electron transport
  chain. MxaG itself does not catalyze methanol oxidation; rather, it mediates electron
  transfer from the MDH redox cofactor PQQ to additional periplasmic cytochromes,
  coupling methanol oxidation to respiration and energy conservation. The gene is part
  of the mxa operon (mxaFJGIRSACKLDEHB) and is subject to the same complex regulatory
  control as mxaFI, being activated by MxbM in the absence of lanthanides and repressed
  when lanthanides are present. Crystal structure has been solved at 1.60 Å resolution
  (PDB: 2C8S), revealing the molecular architecture of this electron transfer protein.'
existing_annotations:
- term:
    id: GO:0005506
    label: iron ion binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Correct - MxaG binds iron in the heme prosthetic group [file:METEA/mxaG/mxaG-uniprot.txt,
      "Binds 1 heme c group covalently per subunit" and "Iron" in keywords]. The UniProt
      feature table specifies the axial iron-coordinating histidine (residue 94, ligand
      Fe), consistent with iron ion binding in a c-type cytochrome heme.
    action: ACCEPT
    reason: The heme c iron is the redox-active center of cytochrome c_L; iron ion binding
      is a correct molecular function supported by the UniProt covalent heme c binding
      sites and the Fe axial-binding residue.
- term:
    id: GO:0009055
    label: electron transfer activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Correct and core - MxaG (cytochrome c_L) functions as the dedicated electron
      acceptor for periplasmic PQQ-dependent methanol dehydrogenase, accepting electrons
      from reduced MxaFI and transferring them onward to additional cytochromes in
      the respiratory electron transport chain [file:METEA/mxaG/mxaG-uniprot.txt, "Electron
      acceptor for MDH. Acts in methanol oxidation"].
    action: ACCEPT
    reason: This is the primary molecular function of the gene product. Multiple authoritative
      sources name MxaG as the cytochrome c_L electron-transfer partner of methanol
      dehydrogenase, transferring electrons from PQQ to downstream cytochromes.
    supported_by:
    - reference_id: file:METEA/mxaG/mxaG-deep-research-falcon.md
      supporting_text: All methylotrophic PQQ-ADHs are periplasmic enzymes associated
        with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons
        from PQQ to additional cytochromes in the electron transport chain
      reference_section_type: OTHER
    - reference_id: file:METEA/mxaG/mxaG-deep-research-falcon.md
      supporting_text: the specific cytochrome c that accepts electrons from methanol
        dehydrogenase
      reference_section_type: OTHER
    - reference_id: file:METEA/mxaG/mxaG-deep-research-falcon.md
      supporting_text: reduced PQQ is reoxidized by transferring electrons to the heme
        of cytochrome cL, which is then oxidized by downstream cytochromes
      reference_section_type: OTHER
- term:
    id: GO:0015945
    label: methanol metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: Correct and core - MxaG participates in methanol metabolism as the electron
      acceptor in the calcium-dependent methanol oxidation pathway, feeding electrons
      from periplasmic methanol oxidation into respiration [file:METEA/mxaG/mxaG-uniprot.txt,
      "Acts in methanol oxidation" and "Methanol utilization" in keywords].
    action: ACCEPT
    reason: MxaG is genetically part of the mxa methanol dehydrogenase cluster and
      functionally required for methanol oxidation by accepting electrons from the
      MDH PQQ cofactor; the deep research confirms its role in the periplasmic methanol-oxidation
      electron-transfer module.
    supported_by:
    - reference_id: file:METEA/mxaG/mxaG-deep-research-falcon.md
      supporting_text: methanol oxidation occurs in the periplasm via PQQ-dependent
        ADHs
      reference_section_type: OTHER
    - reference_id: file:METEA/mxaG/mxaG-deep-research-falcon.md
      supporting_text: Electrons are transferred from PQQ to cytochrome cL and then
        to additional cytochromes/respiratory chain components, coupling methanol oxidation
        to energy generation
      reference_section_type: OTHER
- term:
    id: GO:0020037
    label: heme binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Correct - MxaG contains one heme c group covalently bound per subunit
      [file:METEA/mxaG/mxaG-uniprot.txt, "Binds 1 heme c group covalently per subunit"].
      The covalent heme c is the redox cofactor through which MxaG accepts and donates
      electrons.
    action: ACCEPT
    reason: Covalent heme c binding is documented in UniProt (CXXCH-type c-type cytochrome
      with covalent thioether attachment at residues 90 and 93 and Fe axial coordination
      at residue 94); the heme is essential to its electron-transfer function.
- term:
    id: GO:0042597
    label: periplasmic space
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: 'Correct and core - MxaG is localized to the periplasm where it accepts
      electrons from periplasmic MxaFI [file:METEA/mxaG/mxaG-uniprot.txt, "SUBCELLULAR
      LOCATION: Periplasm"]. It bears an N-terminal signal peptide (residues 1-25)
      consistent with periplasmic export.'
    action: ACCEPT
    reason: UniProt assigns periplasmic localization and a cleaved signal peptide;
      the deep research independently places cytochrome c_L in the periplasmic methanol-oxidation
      electron-transfer chain alongside the periplasmic PQQ-dependent dehydrogenases.
    supported_by:
    - reference_id: file:METEA/mxaG/mxaG-deep-research-falcon.md
      supporting_text: All methylotrophic PQQ-ADHs are periplasmic enzymes associated
        with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons
        from PQQ to additional cytochromes in the electron transport chain
      reference_section_type: OTHER
- term:
    id: GO:0046872
    label: metal ion binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: Correct but general - MxaG binds iron in the heme group. The more specific
      terms GO:0005506 (iron ion binding) and GO:0020037 (heme binding) better capture
      this function.
    action: KEEP_AS_NON_CORE
    reason: This is a redundant generic parent of the iron ion binding annotation already
      present; it is retained as non-core because the specific iron ion binding and
      heme binding terms convey the actual molecular context.
core_functions:
- description: MxaG functions as the dedicated electron acceptor (cytochrome c_L) for
    the calcium-dependent methanol dehydrogenase MxaFI system. The c-type cytochrome
    accepts electrons from reduced MxaFI following methanol oxidation to formaldehyde,
    transferring them via its covalent heme c to downstream respiratory chain components.
    MxaG itself does not catalyze methanol oxidation; rather, it mediates electron
    transfer from the MDH redox cofactor PQQ to additional periplasmic cytochromes.
    MxaG exhibits a redox potential of +256 mV at pH 7.0, which is optimized for efficient
    electron transfer from the calcium-dependent methanol dehydrogenase system. This
    is notably higher than the +172 mV potential of XoxG, the analogous cytochrome
    serving the lanthanide-dependent XoxF system, reflecting the different biochemical
    properties of the two methanol oxidation pathways.
  molecular_function:
    id: GO:0009055
    label: electron transfer activity
  directly_involved_in:
  - id: GO:0015945
    label: methanol metabolic process
  locations:
  - id: GO:0042597
    label: periplasmic space
  supported_by:
  - reference_id: file:METEA/mxaG/mxaG-uniprot.txt
    supporting_text: 'Electron acceptor for MDH. Acts in methanol oxidation...Redox
      potential: E(0) is about +256 mV... SUBCELLULAR LOCATION: Periplasm...Binds
      1 heme c group covalently per subunit'
  - reference_id: file:METEA/mxaG/mxaG-deep-research-falcon.md
    supporting_text: All methylotrophic PQQ-ADHs are periplasmic enzymes associated
      with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons
      from PQQ to additional cytochromes in the electron transport chain
    reference_section_type: OTHER
  - reference_id: file:METEA/mxaG/mxaG-deep-research-falcon.md
    supporting_text: MxaG itself does not catalyze methanol oxidation; rather, it
    reference_section_type: OTHER
references:
- id: file:METEA/mxaG/mxaG-uniprot.txt
  title: UniProt entry for mxaG cytochrome c_L
  findings: []
- id: file:METEA/mxaG/mxaG-deep-research-falcon.md
  title: Falcon deep research report for mxaG (cytochrome c_L) in Methylorubrum extorquens
    AM1
  findings:
  - statement: MxaG (cytochrome c_L) is the cognate periplasmic electron acceptor for
      methylotrophic PQQ-dependent methanol/alcohol dehydrogenases, transferring electrons
      from PQQ to additional cytochromes in the respiratory electron transport chain.
    supporting_text: All methylotrophic PQQ-ADHs are periplasmic enzymes associated
      with a cytochrome cL (MxaG, XoxG, and ExaG, respectively) that transfers electrons
      from PQQ to additional cytochromes in the electron transport chain
    reference_section_type: OTHER
  - statement: The mxa methanol-oxidation gene cluster encodes the specific cytochrome
      c that accepts electrons from methanol dehydrogenase.
    supporting_text: the specific cytochrome c that accepts electrons from methanol
      dehydrogenase
    reference_section_type: OTHER
  - statement: Mechanistically, reduced PQQ is reoxidized by transferring electrons
      to the heme of cytochrome c_L, which is in turn oxidized by downstream cytochromes.
    supporting_text: reduced PQQ is reoxidized by transferring electrons to the heme
      of cytochrome cL, which is then oxidized by downstream cytochromes
    reference_section_type: OTHER
  - statement: MxaG is a shuttle, not a catalyst - it does not itself catalyze methanol
      oxidation but mediates electron transfer from the MDH redox cofactor PQQ to downstream
      respiratory components.
    supporting_text: 'MxaG itself does not catalyze methanol oxidation; rather, it'
    reference_section_type: OTHER
  - statement: Methanol oxidation by the PQQ-dependent dehydrogenases, and hence the
      cytochrome c_L electron-transfer step it feeds, occurs in the periplasm.
    supporting_text: methanol oxidation occurs in the periplasm via PQQ-dependent ADHs
    reference_section_type: OTHER
  - statement: Electron flow proceeds from PQQ to cytochrome c_L and onward to additional
      cytochromes/respiratory chain components, coupling methanol oxidation to energy
      generation.
    supporting_text: Electrons are transferred from PQQ to cytochrome cL and then to
      additional cytochromes/respiratory chain components, coupling methanol oxidation
      to energy generation
    reference_section_type: OTHER
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms.
  findings: []
- id: GO_REF:0000043
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods.
  findings: []
status: COMPLETE

Gene Description

Existing Annotations Review

Core Functions

References

Deep Research

Falcon

Research report: moxG / mxaG (UniProt P14774) in Methylorubrum extorquens AM1

0) Target verification (critical identity check)

1) Key concepts and definitions (current understanding)

1.1 What is cytochrome cL (MxaG/MoxG)?

1.2 PQQ-dependent methanol oxidation and electron transfer

1.3 “MOX/mxa” gene cluster and operon organization

2) Functional annotation of moxG/mxaG: molecular function, pathway role, and localization

2.1 Primary molecular function

2.2 Biological process and pathway placement

2.3 Subcellular localization

3) Recent developments and latest research (emphasis 2023–2024)

3.1 2023: rare-earth element (REE/lanthanide) “switch” and relationship to cytochrome partners

3.2 2024: ecosystem-scale framing of lanthanide methylotrophy (limited mxaG-specific detail)

4) Current applications and real-world implementations

4.1 Engineering and “C1-bioeconomy” context

4.2 Metal/lanthanide-relevant applications (contextual)

5) Expert opinions / authoritative synthesis from high-citation sources

6) Statistics and data points from retrieved studies (recent where possible)

7) Summary of supported annotation (concise)

Evidence map

Artifacts

Citations

📄 View Raw YAML