mxbD

UniProt ID: C5B133
Organism: Methylorubrum extorquens AM1
Review Status: COMPLETE
Aliases:
MexAM1_META1p1753
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Gene Description

Sensor histidine kinase (MxbD) component of the MxbDM two-component regulatory system that controls expression of methanol oxidation genes in Methylorubrum extorquens AM1. MxbD is the sensor histidine kinase and MxbM the cognate response regulator. UniProt-annotated domain architecture comprises two transmembrane regions with HAMP, HisKA (His_kinase_dom) and HATPase_c domains, consistent with a canonical membrane-associated sensor kinase that autophosphorylates a histidine and transfers phosphate to the MxbM response regulator. Functionally, the MxbDM system is required for expression of the mxa operon (Ca-dependent methanol dehydrogenase) and for repression of the lanthanide-responsive xox1 operon in the absence of lanthanides, acting within a regulatory network with MxcQE and the orphan response regulator MxaB. This network underlies the lanthanide ("Ln") switch between Ca-dependent (mxa) and Ln-dependent (xox) methanol dehydrogenase systems. Important caveats: the direct signal sensed by MxbD in AM1, whether its regulatory effects are direct or indirect, and biochemical evidence for phosphorylation state and direct DNA binding by the response regulators remain unresolved in the primary literature; experimental membrane topology/localization in AM1 has not been demonstrated. The MxbD sensing region has been repurposed as a modular methanol-sensing input in engineered chimeric histidine kinases (E. coli biosensors).

Existing Annotations Review

GO Term Evidence Action Reason
GO:0000155 phosphorelay sensor kinase activity
IEA
GO_REF:0000002 		ACCEPT
Summary: Correct. MxbD is the sensor histidine kinase of the MxbDM two-component system; it carries the HisKA dimerization/phospho-acceptor and HATPase_c catalytic domains characteristic of phosphorelay sensor kinases and acts with the cognate response regulator MxbM. The deep-research synthesis consistently identifies MxbD as the sensor histidine kinase component of MxbDM. Note that direct biochemical demonstration of phosphotransfer in AM1 has not been reported (regulatory role is supported by genetics/reporters), but the sensor histidine kinase assignment is well supported by domain architecture and modular-sensor engineering studies.
Supporting Evidence:
file:METEA/mxbD/mxbD-deep-research-falcon.md
**mxbD/MxbD** consistently refers to the **sensor histidine kinase component** of the **MxbDM** two-component regulatory system involved in regulating methanol oxidation gene expression in AM1, with **MxbM** as the cognate response regulator
file:METEA/mxbD/mxbD-deep-research-falcon.md
(i) a **sensor histidine kinase** that autophosphorylates on a histidine residue using ATP and (ii) a **response regulator** that is phosphorylated on an aspartate residue to change gene regulation
GO:0000160 phosphorelay signal transduction system
IEA
GO_REF:0000043 		ACCEPT
Summary: Correct. MxbD and MxbM constitute the MxbDM two-component phosphorelay system. MxbDM acts within a regulatory hierarchy/network with MxcQE and the orphan response regulator MxaB to control methanol dehydrogenase gene expression: it is required for expression of the mxa operon and for repression of the xox1 operon in the absence of lanthanides. Whether the regulatory control is direct or indirect, and the phosphorylation state of the components, remain unresolved in AM1.
Supporting Evidence:
file:METEA/mxbD/mxbD-deep-research-falcon.md
**MxbDM** (MxbD sensor kinase + MxbM response regulator) and **MxcQE** (MxcQ sensor kinase + MxcE response regulator), together with the orphan response regulator **MxaB**, form a regulatory network controlling expression of methanol dehydrogenase systems
file:METEA/mxbD/mxbD-deep-research-falcon.md
the **MxbDM two-component system is required for repression of the xox1 operon in the absence of lanthanides**
GO:0004673 protein histidine kinase activity
IEA
GO_REF:0000003 		ACCEPT
Summary: Correct (EC 2.7.13.3; ATP + protein L-histidine = ADP + protein N-phospho-L-histidine). MxbD is a sensor histidine kinase with HAMP, HisKA and HATPase_c domains and two transmembrane regions. The histidine kinase assignment is reinforced by engineering work in which the MxbD sensing region is swapped into chimeric histidine kinases. Note that in vitro autophosphorylation of AM1 MxbD itself has not been directly demonstrated in the retrieved literature; the assignment rests on domain architecture and conserved two-component logic.
Supporting Evidence:
file:METEA/mxbD/mxbD-deep-research-falcon.md
MxbD is treated as a **sensor histidine kinase** whose “sensing domain” can be modularly swapped into engineered chimeric histidine kinases
GO:0007165 signal transduction
IEA
GO_REF:0000002 		ACCEPT
Summary: Correct. As the sensor kinase of the MxbDM two-component system, MxbD transduces a signal (whose precise identity in AM1 is unresolved) to control transcription of methanol oxidation genes, contributing to the lanthanide-responsive switch between the mxa and xox1 systems. The native input signal (lanthanides directly, methanol/formaldehyde, XoxF metal status, or another cue) remains an open question.
Supporting Evidence:
file:METEA/mxbD/mxbD-deep-research-falcon.md
**MxbD/MxbM** is best supported as a **regulatory (signaling) module**, not a metabolic enzyme: it is a two-component system required for proper expression and reciprocal control of methanol dehydrogenase gene clusters
file:METEA/mxbD/mxbD-deep-research-falcon.md
it is not known if the requirement for these regulators is direct or indirect or what is being sensed by these systems
GO:0016020 membrane
IEA
GO_REF:0000120 		ACCEPT
Summary: Correct (UniProt SUBCELLULAR LOCATION = Membrane; two transmembrane regions predicted). MxbD is a membrane-associated sensor kinase. Note that experimental validation of membrane topology/localization specifically in AM1 was not identified in the retrieved literature; the assignment rests on sequence/topology prediction and the canonical architecture of sensor histidine kinases.
Supporting Evidence:
file:METEA/mxbD/mxbD-deep-research-falcon.md
it is expected to function at the **cell envelope–cytosol signaling interface**, but **experimental validation of membrane topology/localization in AM1 is lacking** in the evidence retrieved here
GO:0016301 kinase activity
IEA
GO_REF:0000043 		ACCEPT
Summary: Correct but general. MxbD is a histidine (protein) kinase; the more specific terms GO:0004673 (protein histidine kinase activity) and GO:0000155 (phosphorelay sensor kinase activity) better capture its function. Retained as a true but high-level parent.
GO:0016740 transferase activity
IEA
GO_REF:0000043 		ACCEPT
Summary: Correct but very general. This is a high-level parent of the histidine kinase activity; the specific child terms (GO:0004673, GO:0000155) are the informative annotations. Retained as a true but uninformative parent.
GO:0016772 transferase activity, transferring phosphorus-containing groups
IEA
GO_REF:0000002 		ACCEPT
Summary: Correct but general. Parent of histidine kinase activity (transfers phosphate from ATP to a histidine residue, then to the MxbM response regulator). The specific MF terms GO:0004673 and GO:0000155 are preferred. Retained as a true but high-level parent.

Core Functions

Sensor histidine kinase of the MxbDM two-component system that signals to control transcription of methanol oxidation genes (mxa/xox1) in a lanthanide-responsive regulatory network

Molecular Function:
phosphorelay sensor kinase activity
Cellular Locations:
membrane
Supporting Evidence:
  • file:METEA/mxbD/mxbD-deep-research-falcon.md
    **mxbD/MxbD** consistently refers to the **sensor histidine kinase component** of the **MxbDM** two-component regulatory system involved in regulating methanol oxidation gene expression in AM1, with **MxbM** as the cognate response regulator

Histidine autokinase / phosphotransfer activity of the MxbDM two-component system controlling methanol dehydrogenase gene expression - required for mxa operon expression and repression of the xox1 operon in the absence of lanthanides, acting with MxcQE and MxaB

Molecular Function:
protein histidine kinase activity
Supporting Evidence:
  • file:METEA/mxbD/mxbD-deep-research-falcon.md
    MxbDM participates in the lanthanide-responsive transcriptional network controlling methanol oxidation systems, specifically supporting **mxa operon expression** and contributing to **repression of xox1 in lanthanide-free conditions**

References

GO_REF:0000002
Gene Ontology annotation through association of InterPro records with GO terms.
GO_REF:0000003
Gene Ontology annotation based on Enzyme Commission mapping
GO_REF:0000043
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
GO_REF:0000120
Combined Automated Annotation using Multiple IEA Methods.
file:METEA/mxbD/mxbD-deep-research-falcon.md
Falcon (Edison Scientific) deep research report: Methylorubrum extorquens AM1 mxbD (UniProt C5B133) functional annotation
  • "**mxbD/MxbD** consistently refers to the **sensor histidine kinase component** of the **MxbDM** two-component regulatory system involved in regulating methanol oxidation gene expression in AM1, with **MxbM** as the cognate response regulator"
  • "**MxbDM** (MxbD sensor kinase + MxbM response regulator) and **MxcQE** (MxcQ sensor kinase + MxcE response regulator), together with the orphan response regulator **MxaB**, form a regulatory network controlling expression of methanol dehydrogenase systems"
  • "the response regulator **MxbM** is described as **required for expression of the mxa operon**, alongside MxcQE and MxaB"
  • "the **MxbDM two-component system is required for repression of the xox1 operon in the absence of lanthanides**; the Skovran review further emphasizes that **MxbM is uniquely required for repression of xox1** in the described network"
  • "**MxbD/MxbM** is best supported as a **regulatory (signaling) module**, not a metabolic enzyme: it is a two-component system required for proper expression and reciprocal control of methanol dehydrogenase gene clusters"
  • "it is not known if the requirement for these regulators is direct or indirect or what is being sensed by these systems"
  • "neither the phosphorylation state nor direct DNA binding by these response regulators has been shown"
  • "it is expected to function at the **cell envelope–cytosol signaling interface**, but **experimental validation of membrane topology/localization in AM1 is lacking** in the evidence retrieved here"
  • "The authors fused the **“methanol-sensing domain” of MxbD** (from *M. extorquens*) with the transmitter domain of *E. coli* EnvZ to create a chimeric histidine kinase (MxbDZ)"

Deep Research

Falcon

(mxbD-deep-research-falcon.md)
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 19 citations 2 artifacts 2026-06-03T09:51:43.395029
Edison artifact artifact-00 (text/markdown)
## Context ID: pqac-00000008 Figure 8 provides a schematic hypothesis for the lanthanide-dependent regulation (Ln switch) of the *mxa* and *xox1* operons in *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: functional annotation of mxbD (UniProt C5B133) in Methylorubrum extorquens AM1

1) Identity verification and scope control (critical disambiguation)

The target described by UniProt accession C5B133 is annotated as a histidine kinase (EC 2.7.13.3) encoded by mxbD in Methylorubrum extorquens strain AM1 (a.k.a. Methylobacterium extorquens AM1). In the accessible literature corpus retrieved here, mxbD/MxbD consistently refers to the sensor histidine kinase component of the MxbDM two-component regulatory system involved in regulating methanol oxidation gene expression in AM1, with MxbM as the cognate response regulator; no conflicting “mxbD” identity from other organisms was encountered in the evidence extracted. (skovran2019lanthanidesinmethylotrophy pages 6-8, dubey2019mnosrisa pages 25-28, vu2016lanthanidedependentregulationof pages 6-9)

Limitations: the retrieved full-text sources did not contain the UniProt/InterPro domain-by-domain description needed to independently confirm the reported HAMP/HATPase/HisKA-like architecture from sequence annotations. Therefore, domain architecture is treated as UniProt-provided context rather than re-validated from primary sequence analysis in this run.

2) Key concepts and definitions (current understanding)

Two-component systems (TCS) and histidine kinases

Two-component systems typically comprise (i) a sensor histidine kinase that autophosphorylates on a histidine residue using ATP and (ii) a response regulator that is phosphorylated on an aspartate residue to change gene regulation. In AM1 methylotrophy, MxbDM (MxbD sensor kinase + MxbM response regulator) and MxcQE (MxcQ sensor kinase + MxcE response regulator), together with the orphan response regulator MxaB, form a regulatory network controlling expression of methanol dehydrogenase systems. (skovran2019lanthanidesinmethylotrophy pages 6-8, vu2016lanthanidedependentregulationof pages 6-9)

“Ln switch” (lanthanide switch) in methylotrophs

AM1 encodes methanol dehydrogenase systems whose transcription responds strongly to lanthanides (Ln). Vu et al. experimentally demonstrated that in AM1, xox1 transcriptional activation is detectable at ~2.5 nM La and reaches a maximum by ~250 nM La, while repression of the mxa promoter begins between 25–50 nM La and is fully repressed at ~250 nM La (with no further change up to 20 μM La). This defines a quantitatively steep Ln-responsive transcriptional switch between mxa and xox1. (vu2016lanthanidedependentregulationof pages 14-18)

3) Biological function and pathway placement of MxbD (AM1)

Primary functional role (best-supported)

Across AM1-focused sources, MxbD/MxbM is best supported as a regulatory (signaling) module, not a metabolic enzyme: it is a two-component system required for proper expression and reciprocal control of methanol dehydrogenase gene clusters.

  • Activation of the Ca-dependent methanol dehydrogenase system (mxa): the response regulator MxbM is described as required for expression of the mxa operon, alongside MxcQE and MxaB. (skovran2019lanthanidesinmethylotrophy pages 6-8, vu2016lanthanidedependentregulationof pages 6-9)
  • Repression of the lanthanide-responsive xox1 operon in Ln-free conditions: Vu et al. state that the MxbDM two-component system is required for repression of the xox1 operon in the absence of lanthanides; the Skovran review further emphasizes that MxbM is uniquely required for repression of xox1 in the described network. (vu2016lanthanidedependentregulationof pages 6-9, skovran2019lanthanidesinmethylotrophy pages 6-8)

Proposed regulatory model linking XoxF and MxbDM (current working hypothesis)

Vu et al. propose a model in which apo-XoxF (XoxF lacking a lanthanide cofactor) can act as a sensor for lanthanide presence by interacting (directly or indirectly) with the two-component systems MxcQE and MxbDM, such that:

  • Without lanthanides: “apo-XoxF activates expression of the mxa genes and represses expression of the xox1 genes as mediated through the two-component systems MxcQE and MxbDM.” (vu2016lanthanidedependentregulationof pages 31-40)
  • With lanthanides: XoxF binds the metal, resumes a catalytic role, and becomes unavailable (or conformationally unable) to interact with the TCSs, leading to repression of mxa and activation of xox1. (vu2016lanthanidedependentregulationof pages 31-40)

A schematic of this Ln-switch hypothesis (with MxbDM and MxcQE explicitly depicted) is provided in Vu et al. (Figure 8). (vu2016lanthanidedependentregulationof media 5459bc04)

4) Mechanism: what is known vs unknown (expert assessment)

A recurring expert assessment in both a primary study (Vu 2016) and an authoritative review (Skovran 2019) is that key mechanistic details of MxbDM remain unresolved:

  • Vu et al. explicitly state “it is not known if the requirement for these regulators is direct or indirect or what is being sensed by these systems.” (vu2016lanthanidedependentregulationof pages 6-9)
  • The Skovran review emphasizes that direct binding of these regulators to promoters has not been demonstrated, and “neither the phosphorylation state nor direct DNA binding by these response regulators has been shown” in the literature summarized there. (skovran2019lanthanidesinmethylotrophy pages 6-8)

Interpretation: While MxbD is annotated and used as a histidine kinase sensor in a canonical TCS architecture, the native input signal to MxbD in AM1 (lanthanide ions directly, methanol, formaldehyde, XoxF/metal status, or another periplasmic/cellular cue) remains an open question in the AM1 system, and regulatory connections are supported largely through genetics/reporters and network inference rather than direct biochemical reconstitution of phosphotransfer/DNA-binding.

5) Cellular localization/topology

Direct experimental localization/topology for AM1 MxbD was not identified in the retrieved full-text excerpts. However, MxbD is treated as a sensor histidine kinase whose “sensing domain” can be modularly swapped into engineered chimeric histidine kinases (see Applications below), which is consistent with (but does not prove) a typical HK architecture where an N-terminal sensor region (often membrane/periplasm-associated) is coupled to a cytosolic kinase transmitter. (selvamani2020engineeringofrecombinant pages 1-3, selvamani2020engineeringofrecombinant pages 3-5)

Accordingly, a cautious functional-annotation statement supported by literature is:
* Localization inference: MxbD is a signaling protein belonging to a two-component system regulating transcription; it is expected to function at the cell envelope–cytosol signaling interface, but experimental validation of membrane topology/localization in AM1 is lacking in the evidence retrieved here. (vu2016lanthanidedependentregulationof pages 6-9, skovran2019lanthanidesinmethylotrophy pages 6-8)

6) Recent developments and latest research (prioritizing 2023–2024)

Direct 2023–2024 primary literature specifically dissecting MxbD biochemistry in AM1 was not retrieved in this run. However, 2023 research continues to expand the broader conceptual landscape in which MxbDM operates—lanthanide-regulated methylotrophy and methanol-linked behaviors:

  • Methanol metabolism-linked chemotaxis and plant colonization (2023): In Methylobacterium aquaticum strain 22A, Tani et al. report that methylotaxis depends on multiple methyl-accepting chemotaxis proteins (MCPs) and that one MCP (MtpC) is regulated under MxbDM, linking methanol oxidation state and regulatory networks to host colonization behavior in a plant-associated methylobacterium. While not AM1, it underscores that MxbDM-like regulation is leveraged in related taxa for methanol-associated ecological traits. (Published Oct 2023; URL: https://doi.org/10.3389/fmicb.2023.1258452) (tani2023metabolismlinkedmethylotaxissensors pages 2-3)

  • Ln-dependent and Ln-responsive physiology continues to broaden beyond AM1 (2023–2024): Work in diverse bacteria (e.g., a novel lanthanide-accumulating methylotroph and a non-methylotroph model) emphasizes that Ln can reprogram substantial portions of bacterial transcriptomes and that Ln sensing/signaling can discriminate between different Ln elements—contextually supporting why AM1’s Ln-responsive regulatory network (including MxbDM) remains an active research frontier. (Dec 2023; URL: https://doi.org/10.1128/spectrum.00867-23) (Oct 2024; URL: https://doi.org/10.1128/msphere.00685-24) (These papers were retrieved but do not provide AM1-specific mechanistic detail on MxbD.)

7) Current applications and real-world implementations

Synthetic biology: methanol biosensing via MxbD-derived sensing modules

A concrete implementation using MxbD as a modular sensor is demonstrated by Selvamani et al. (2020), who engineered E. coli methanol biosensors using domain swapping.

  • The authors fused the “methanol-sensing domain” of MxbD (from M. extorquens) with the transmitter domain of E. coli EnvZ to create a chimeric histidine kinase (MxbDZ). The chimeric kinase signals via OmpR to activate the ompC promoter driving GFP. (Published Mar 2020; URL: https://doi.org/10.4014/mbl.1908.08009) (selvamani2020engineeringofrecombinant pages 1-3, selvamani2020engineeringofrecombinant pages 3-5)
  • Quantitative operating regime: the engineered system was tested across 0–8% methanol, and the authors report maximum fluorescence at 0.05% methanol for MxbDZ (and 0.01% for a separate MxcQ-based chimera). (selvamani2020engineeringofrecombinant pages 1-3, selvamani2020engineeringofrecombinant pages 3-5)

Relevance to functional annotation: this supports that MxbD contains an input/sensing region that can be repurposed as a modular sensor in heterologous TCS architectures, consistent with its annotation as a sensor histidine kinase. (selvamani2020engineeringofrecombinant pages 1-3)

8) Relevant statistics and data points (from recent/authoritative studies)

Key quantitative findings supporting pathway-level annotation:

  • Lanthanide thresholds for transcriptional switching in AM1:
  • xox1 promoter activation detectable at ~2.5 nM La, maximal by ~250 nM La.
  • mxa promoter repression begins 25–50 nM La, full repression by ~250 nM La.

  • Distinct lanthanides (La, Ce, Pr, Nd) reproduce the differential expression pattern; Sm has only a small effect. (Apr 2016; URL: https://doi.org/10.1128/jb.00937-15) (vu2016lanthanidedependentregulationof pages 14-18)

  • Methanol biosensor response regime using MxbD-derived sensing (heterologous system):

  • tested 0–8% methanol; maximal fluorescence at 0.05% methanol for the MxbD-based chimera. (Mar 2020; URL: https://doi.org/10.4014/mbl.1908.08009) (selvamani2020engineeringofrecombinant pages 1-3, selvamani2020engineeringofrecombinant pages 3-5)

9) Consolidated functional annotation (evidence-based)

Gene/product: mxbD encodes MxbD, a sensor histidine kinase that forms the MxbDM two-component system with response regulator MxbM in Methylorubrum extorquens AM1. (skovran2019lanthanidesinmethylotrophy pages 6-8, vu2016lanthanidedependentregulationof pages 6-9)

Primary role in AM1: MxbDM participates in the lanthanide-responsive transcriptional network controlling methanol oxidation systems, specifically supporting mxa operon expression and contributing to repression of xox1 in lanthanide-free conditions. (vu2016lanthanidedependentregulationof pages 6-9)

Pathway context: MxbDM acts together with MxcQE and MxaB in regulating methanol dehydrogenase gene expression, within a lanthanide switch framework where lanthanide availability tunes expression of Ca-dependent (mxa) vs Ln-dependent (xox) methanol dehydrogenases. (vu2016lanthanidedependentregulationof pages 6-9, vu2016lanthanidedependentregulationof pages 14-18)

Mechanistic status: The direct signal sensed by MxbD, whether regulation is direct vs indirect, and biochemical evidence for phosphorylation state and direct DNA binding by response regulators remain unresolved in the cited AM1 literature synthesis. (skovran2019lanthanidesinmethylotrophy pages 6-8, vu2016lanthanidedependentregulationof pages 6-9)

10) Evidence map (summary table)

Topic Key points Best supporting sources (with year)
MxbD/MxbM function in Methylorubrum extorquens AM1 MxbD is the sensor histidine kinase and MxbM the cognate response regulator of the MxbDM two-component system implicated in methanol oxidation gene regulation. The system is required for proper expression of methanol oxidation functions in AM1 and is positioned within a broader regulatory network with MxcQE and MxaB. Skovran et al. 2019 review summarizing primary genetics; Springer et al. 1997 primary study cited therein (skovran2019lanthanidesinmethylotrophy pages 6-8, dubey2019mnosrisa pages 25-28)
Regulatory targets: mxa operon MxbDM is required for expression of the mxa operon encoding the Ca-dependent methanol dehydrogenase system; MxbM is specifically described as required for mxa expression. MxcQE and MxaB also contribute to mxa activation, suggesting a multilayer cascade rather than a simple one-step control pathway. Skovran et al. 2019; Vu et al. 2016 (skovran2019lanthanidesinmethylotrophy pages 6-8, vu2016lanthanidedependentregulationof pages 6-9)
Regulatory targets: xox1 operon In AM1, MxbDM is required to repress the xox1 operon under lanthanide-free conditions; MxbM is highlighted as uniquely required for xox1 repression in the reviewed model. This places MxbDM at the center of the inverse regulation between Ca-dependent mxa and Ln-dependent xox methanol dehydrogenase systems. Skovran et al. 2019; Vu et al. 2016 (skovran2019lanthanidesinmethylotrophy pages 6-8, vu2016lanthanidedependentregulationof pages 6-9)
Lanthanide dependence / Ln-switch model The best-supported current model is a lanthanide switch: without Ln, apo-XoxF is proposed to help drive mxa expression and xox1 repression through MxcQE/MxbDM-linked signaling; with Ln present, XoxF becomes the active Ln-dependent enzyme and regulation flips toward xox1 expression and mxa repression. Expression from mxa and xox1 promoters is highly sensitive to Ln such as La, Ce, Pr, and Nd. Vu et al. 2016 and its regulatory schematic; Skovran et al. 2019 (vu2016lanthanidedependentregulationof pages 6-9, vu2016lanthanidedependentregulationof media 5459bc04, skovran2019lanthanidesinmethylotrophy pages 6-8)
Known vs unknown mechanism Known: MxbDM is a two-component regulatory pair associated with methanol metabolism and Ln-responsive regulation of mxa/xox expression. Unknown/uncertain: the direct signal sensed by MxbD in native AM1 remains unresolved; whether control is direct or indirect is still unclear; the phosphorylation state of MxbD/MxbM and direct DNA binding by these regulators had not been demonstrated in the cited review literature. Vu et al. 2016; Skovran et al. 2019 (vu2016lanthanidedependentregulationof pages 6-9, skovran2019lanthanidesinmethylotrophy pages 6-8)
Domain/function inference for MxbD Independently of unresolved native mechanism, MxbD is treated as a histidine kinase sensor component, consistent with two-component signaling logic and with engineering studies that use its input/sensing region as a modular sensor fused to another kinase transmitter domain. This supports functional annotation as a membrane-associated/environmental sensor rather than a catalytic methanol-oxidizing enzyme. Selvamani et al. 2020; Skovran et al. 2019 (selvamani2020engineeringofrecombinant pages 1-3, selvamani2020engineeringofrecombinant pages 3-5, skovran2019lanthanidesinmethylotrophy pages 6-8)
Real-world application: methanol biosensor chimeras MxbD has been repurposed in engineered E. coli methanol biosensors by fusing the MxbD sensing region to the EnvZ transmitter. The resulting chimeric kinase activated OmpR/ompC and GFP output, with reported maximal fluorescence at 0.05% methanol for MxbDZ; assays tested 0-8% methanol, demonstrating practical use of MxbD-derived sensing for synthetic biology. Selvamani et al. 2020 (selvamani2020engineeringofrecombinant pages 1-3, selvamani2020engineeringofrecombinant pages 3-5)

Table: This table condenses the best-supported evidence on MxbD/MxbM in Methylorubrum extorquens AM1, emphasizing regulatory role, lanthanide-responsive control of mxa/xox1, major mechanistic uncertainties, and a concrete biosensor application.

Key visual evidence (model schematic)

Vu et al. provide a schematic hypothesis of the Ln switch and the proposed role of MxbDM/MxcQE in mediating opposite regulation of mxa vs xox1 depending on lanthanide availability. (vu2016lanthanidedependentregulationof media 5459bc04)

References (URLs and publication dates as available in retrieved sources)

  • Vu HN et al. Lanthanide-Dependent Regulation of Methanol Oxidation Systems in Methylobacterium extorquens AM1… Journal of Bacteriology (Apr 2016). https://doi.org/10.1128/jb.00937-15 (vu2016lanthanidedependentregulationof pages 6-9, vu2016lanthanidedependentregulationof pages 31-40, vu2016lanthanidedependentregulationof pages 14-18)
  • Skovran E et al. Lanthanides in methylotrophy. Current Issues in Molecular Biology (Jan 2019). https://doi.org/10.21775/cimb.033.101 (skovran2019lanthanidesinmethylotrophy pages 6-8)
  • Selvamani V et al. Engineering of recombinant Escherichia coli towards methanol sensing using Methylobacterium extroquens two-component systems. (Mar 2020). https://doi.org/10.4014/mbl.1908.08009 (selvamani2020engineeringofrecombinant pages 1-3, selvamani2020engineeringofrecombinant pages 3-5)
  • Tani A et al. Metabolism-linked methylotaxis sensors responsible for plant colonization in Methylobacterium aquaticum strain 22A. Frontiers in Microbiology (Oct 2023). https://doi.org/10.3389/fmicb.2023.1258452 (tani2023metabolismlinkedmethylotaxissensors pages 2-3)

References

  1. (skovran2019lanthanidesinmethylotrophy pages 6-8): Elizabeth Skovran, Charumathi Raghuraman, and Norma Cecilia Martinez-Gomez. Lanthanides in methylotrophy. Current issues in molecular biology, 33:101-116, Jan 2019. URL: https://doi.org/10.21775/cimb.033.101, doi:10.21775/cimb.033.101. This article has 49 citations.

  2. (dubey2019mnosrisa pages 25-28): Abhishek Anil Dubey and Vikas Jain. Mnosr is a bona fide two-component system involved in methylotrophic metabolism in mycobacterium smegmatis. Applied and Environmental Microbiology, Jul 2019. URL: https://doi.org/10.1128/aem.00535-19, doi:10.1128/aem.00535-19. This article has 16 citations and is from a peer-reviewed journal.

  3. (vu2016lanthanidedependentregulationof pages 6-9): Huong N. Vu, Gabriel A. Subuyuj, Srividhya Vijayakumar, Nathan M. Good, N. Cecilia Martinez-Gomez, and Elizabeth Skovran. Lanthanide-dependent regulation of methanol oxidation systems in methylobacterium extorquens am1 and their contribution to methanol growth. Journal of Bacteriology, 198:1250-1259, Apr 2016. URL: https://doi.org/10.1128/jb.00937-15, doi:10.1128/jb.00937-15. This article has 227 citations and is from a peer-reviewed journal.

  4. (vu2016lanthanidedependentregulationof pages 14-18): Huong N. Vu, Gabriel A. Subuyuj, Srividhya Vijayakumar, Nathan M. Good, N. Cecilia Martinez-Gomez, and Elizabeth Skovran. Lanthanide-dependent regulation of methanol oxidation systems in methylobacterium extorquens am1 and their contribution to methanol growth. Journal of Bacteriology, 198:1250-1259, Apr 2016. URL: https://doi.org/10.1128/jb.00937-15, doi:10.1128/jb.00937-15. This article has 227 citations and is from a peer-reviewed journal.

  5. (vu2016lanthanidedependentregulationof pages 31-40): Huong N. Vu, Gabriel A. Subuyuj, Srividhya Vijayakumar, Nathan M. Good, N. Cecilia Martinez-Gomez, and Elizabeth Skovran. Lanthanide-dependent regulation of methanol oxidation systems in methylobacterium extorquens am1 and their contribution to methanol growth. Journal of Bacteriology, 198:1250-1259, Apr 2016. URL: https://doi.org/10.1128/jb.00937-15, doi:10.1128/jb.00937-15. This article has 227 citations and is from a peer-reviewed journal.

  6. (vu2016lanthanidedependentregulationof media 5459bc04): Huong N. Vu, Gabriel A. Subuyuj, Srividhya Vijayakumar, Nathan M. Good, N. Cecilia Martinez-Gomez, and Elizabeth Skovran. Lanthanide-dependent regulation of methanol oxidation systems in methylobacterium extorquens am1 and their contribution to methanol growth. Journal of Bacteriology, 198:1250-1259, Apr 2016. URL: https://doi.org/10.1128/jb.00937-15, doi:10.1128/jb.00937-15. This article has 227 citations and is from a peer-reviewed journal.

  7. (selvamani2020engineeringofrecombinant pages 1-3): Vidhya Selvamani, Irisappan Ganesh, Sowon Chae, Murali kannan Maruthamuthu, and Soon Ho Hong. Engineering of recombinant escherichia coli towards methanol sensing using methylobacterium extroquens two-component systems. ArXiv, 48:24-31, Mar 2020. URL: https://doi.org/10.4014/mbl.1908.08009, doi:10.4014/mbl.1908.08009. This article has 3 citations.

  8. (selvamani2020engineeringofrecombinant pages 3-5): Vidhya Selvamani, Irisappan Ganesh, Sowon Chae, Murali kannan Maruthamuthu, and Soon Ho Hong. Engineering of recombinant escherichia coli towards methanol sensing using methylobacterium extroquens two-component systems. ArXiv, 48:24-31, Mar 2020. URL: https://doi.org/10.4014/mbl.1908.08009, doi:10.4014/mbl.1908.08009. This article has 3 citations.

  9. (tani2023metabolismlinkedmethylotaxissensors pages 2-3): Akio Tani, Sachiko Masuda, Yoshiko Fujitani, Toshiki Iga, Yuuki Haruna, Shiho Kikuchi, Wang Shuaile, Haoxin Lv, Shiori Katayama, Hiroya Yurimoto, Yasuyoshi Sakai, and Junichi Kato. Metabolism-linked methylotaxis sensors responsible for plant colonization in methylobacterium aquaticum strain 22a. Frontiers in Microbiology, Oct 2023. URL: https://doi.org/10.3389/fmicb.2023.1258452, doi:10.3389/fmicb.2023.1258452. This article has 13 citations and is from a peer-reviewed journal.

Artifacts

Citations

  1. vu2016lanthanidedependentregulationof pages 14-18
  2. vu2016lanthanidedependentregulationof pages 31-40
  3. vu2016lanthanidedependentregulationof pages 6-9
  4. skovran2019lanthanidesinmethylotrophy pages 6-8
  5. tani2023metabolismlinkedmethylotaxissensors pages 2-3
  6. selvamani2020engineeringofrecombinant pages 1-3
  7. dubey2019mnosrisa pages 25-28
  8. selvamani2020engineeringofrecombinant pages 3-5
  9. https://doi.org/10.3389/fmicb.2023.1258452
  10. https://doi.org/10.1128/spectrum.00867-23
  11. https://doi.org/10.1128/msphere.00685-24
  12. https://doi.org/10.4014/mbl.1908.08009
  13. https://doi.org/10.1128/jb.00937-15
  14. https://doi.org/10.21775/cimb.033.101
  15. https://doi.org/10.21775/cimb.033.101,
  16. https://doi.org/10.1128/aem.00535-19,
  17. https://doi.org/10.1128/jb.00937-15,
  18. https://doi.org/10.4014/mbl.1908.08009,
  19. https://doi.org/10.3389/fmicb.2023.1258452,

📄 View Raw YAML

 
id: C5B133
gene_symbol: mxbD
aliases:
- MexAM1_META1p1753
product_type: PROTEIN
taxon:
  id: NCBITaxon:272630
  label: Methylorubrum extorquens AM1
description: 'Sensor histidine kinase (MxbD) component of the MxbDM two-component
  regulatory system that controls expression of methanol oxidation genes in Methylorubrum
  extorquens AM1. MxbD is the sensor histidine kinase and MxbM the cognate response
  regulator. UniProt-annotated domain architecture comprises two transmembrane regions
  with HAMP, HisKA (His_kinase_dom) and HATPase_c domains, consistent with a canonical
  membrane-associated sensor kinase that autophosphorylates a histidine and transfers
  phosphate to the MxbM response regulator. Functionally, the MxbDM system is required
  for expression of the mxa operon (Ca-dependent methanol dehydrogenase) and for repression
  of the lanthanide-responsive xox1 operon in the absence of lanthanides, acting within
  a regulatory network with MxcQE and the orphan response regulator MxaB. This network
  underlies the lanthanide ("Ln") switch between Ca-dependent (mxa) and Ln-dependent
  (xox) methanol dehydrogenase systems. Important caveats: the direct signal sensed
  by MxbD in AM1, whether its regulatory effects are direct or indirect, and biochemical
  evidence for phosphorylation state and direct DNA binding by the response regulators
  remain unresolved in the primary literature; experimental membrane topology/localization
  in AM1 has not been demonstrated. The MxbD sensing region has been repurposed as a
  modular methanol-sensing input in engineered chimeric histidine kinases (E. coli
  biosensors).'
existing_annotations:
- term:
    id: GO:0000155
    label: phosphorelay sensor kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Correct. MxbD is the sensor histidine kinase of the MxbDM two-component
      system; it carries the HisKA dimerization/phospho-acceptor and HATPase_c catalytic
      domains characteristic of phosphorelay sensor kinases and acts with the cognate
      response regulator MxbM. The deep-research synthesis consistently identifies MxbD
      as the sensor histidine kinase component of MxbDM. Note that direct biochemical
      demonstration of phosphotransfer in AM1 has not been reported (regulatory role
      is supported by genetics/reporters), but the sensor histidine kinase assignment
      is well supported by domain architecture and modular-sensor engineering studies.
    action: ACCEPT
    supported_by:
    - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
      supporting_text: |-
        **mxbD/MxbD** consistently refers to the **sensor histidine kinase component** of the **MxbDM** two-component regulatory system involved in regulating methanol oxidation gene expression in AM1, with **MxbM** as the cognate response regulator
    - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
      supporting_text: |-
        (i) a **sensor histidine kinase** that autophosphorylates on a histidine residue using ATP and (ii) a **response regulator** that is phosphorylated on an aspartate residue to change gene regulation
- term:
    id: GO:0000160
    label: phosphorelay signal transduction system
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: 'Correct. MxbD and MxbM constitute the MxbDM two-component phosphorelay
      system. MxbDM acts within a regulatory hierarchy/network with MxcQE and the orphan
      response regulator MxaB to control methanol dehydrogenase gene expression: it is
      required for expression of the mxa operon and for repression of the xox1 operon
      in the absence of lanthanides. Whether the regulatory control is direct or indirect,
      and the phosphorylation state of the components, remain unresolved in AM1.'
    action: ACCEPT
    supported_by:
    - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
      supporting_text: |-
        **MxbDM** (MxbD sensor kinase + MxbM response regulator) and **MxcQE** (MxcQ sensor kinase + MxcE response regulator), together with the orphan response regulator **MxaB**, form a regulatory network controlling expression of methanol dehydrogenase systems
    - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
      supporting_text: |-
        the **MxbDM two-component system is required for repression of the xox1 operon in the absence of lanthanides**
- term:
    id: GO:0004673
    label: protein histidine kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000003
  review:
    summary: Correct (EC 2.7.13.3; ATP + protein L-histidine = ADP + protein N-phospho-L-histidine).
      MxbD is a sensor histidine kinase with HAMP, HisKA and HATPase_c domains and two
      transmembrane regions. The histidine kinase assignment is reinforced by engineering
      work in which the MxbD sensing region is swapped into chimeric histidine kinases.
      Note that in vitro autophosphorylation of AM1 MxbD itself has not been directly
      demonstrated in the retrieved literature; the assignment rests on domain architecture
      and conserved two-component logic.
    action: ACCEPT
    supported_by:
    - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
      supporting_text: |-
        MxbD is treated as a **sensor histidine kinase** whose “sensing domain” can be modularly swapped into engineered chimeric histidine kinases
- term:
    id: GO:0007165
    label: signal transduction
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Correct. As the sensor kinase of the MxbDM two-component system, MxbD transduces
      a signal (whose precise identity in AM1 is unresolved) to control transcription
      of methanol oxidation genes, contributing to the lanthanide-responsive switch
      between the mxa and xox1 systems. The native input signal (lanthanides directly,
      methanol/formaldehyde, XoxF metal status, or another cue) remains an open question.
    action: ACCEPT
    supported_by:
    - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
      supporting_text: |-
        **MxbD/MxbM** is best supported as a **regulatory (signaling) module**, not a metabolic enzyme: it is a two-component system required for proper expression and reciprocal control of methanol dehydrogenase gene clusters
    - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
      supporting_text: |-
        it is not known if the requirement for these regulators is direct or indirect or what is being sensed by these systems
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: Correct (UniProt SUBCELLULAR LOCATION = Membrane; two transmembrane regions
      predicted). MxbD is a membrane-associated sensor kinase. Note that experimental
      validation of membrane topology/localization specifically in AM1 was not identified
      in the retrieved literature; the assignment rests on sequence/topology prediction
      and the canonical architecture of sensor histidine kinases.
    action: ACCEPT
    supported_by:
    - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
      supporting_text: |-
        it is expected to function at the **cell envelope–cytosol signaling interface**, but **experimental validation of membrane topology/localization in AM1 is lacking** in the evidence retrieved here
- term:
    id: GO:0016301
    label: kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: Correct but general. MxbD is a histidine (protein) kinase; the more specific
      terms GO:0004673 (protein histidine kinase activity) and GO:0000155 (phosphorelay
      sensor kinase activity) better capture its function. Retained as a true but
      high-level parent.
    action: ACCEPT
- term:
    id: GO:0016740
    label: transferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: Correct but very general. This is a high-level parent of the histidine
      kinase activity; the specific child terms (GO:0004673, GO:0000155) are the
      informative annotations. Retained as a true but uninformative parent.
    action: ACCEPT
- term:
    id: GO:0016772
    label: transferase activity, transferring phosphorus-containing groups
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Correct but general. Parent of histidine kinase activity (transfers phosphate
      from ATP to a histidine residue, then to the MxbM response regulator). The specific
      MF terms GO:0004673 and GO:0000155 are preferred. Retained as a true but
      high-level parent.
    action: ACCEPT
core_functions:
- description: Sensor histidine kinase of the MxbDM two-component system that signals
    to control transcription of methanol oxidation genes (mxa/xox1) in a lanthanide-responsive
    regulatory network
  molecular_function:
    id: GO:0000155
    label: phosphorelay sensor kinase activity
  supported_by:
  - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
    supporting_text: |-
      **mxbD/MxbD** consistently refers to the **sensor histidine kinase component** of the **MxbDM** two-component regulatory system involved in regulating methanol oxidation gene expression in AM1, with **MxbM** as the cognate response regulator
  locations:
  - id: GO:0016020
    label: membrane
- description: Histidine autokinase / phosphotransfer activity of the MxbDM two-component
    system controlling methanol dehydrogenase gene expression - required for mxa operon
    expression and repression of the xox1 operon in the absence of lanthanides, acting
    with MxcQE and MxaB
  molecular_function:
    id: GO:0004673
    label: protein histidine kinase activity
  supported_by:
  - reference_id: file:METEA/mxbD/mxbD-deep-research-falcon.md
    supporting_text: |-
      MxbDM participates in the lanthanide-responsive transcriptional network controlling methanol oxidation systems, specifically supporting **mxa operon expression** and contributing to **repression of xox1 in lanthanide-free conditions**
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms.
  findings: []
- id: GO_REF:0000003
  title: Gene Ontology annotation based on Enzyme Commission mapping
  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: []
- id: file:METEA/mxbD/mxbD-deep-research-falcon.md
  title: 'Falcon (Edison Scientific) deep research report: Methylorubrum extorquens
    AM1 mxbD (UniProt C5B133) functional annotation'
  findings:
  - reference_section_type: OTHER
    supporting_text: |-
      **mxbD/MxbD** consistently refers to the **sensor histidine kinase component** of the **MxbDM** two-component regulatory system involved in regulating methanol oxidation gene expression in AM1, with **MxbM** as the cognate response regulator
  - reference_section_type: OTHER
    supporting_text: |-
      **MxbDM** (MxbD sensor kinase + MxbM response regulator) and **MxcQE** (MxcQ sensor kinase + MxcE response regulator), together with the orphan response regulator **MxaB**, form a regulatory network controlling expression of methanol dehydrogenase systems
  - reference_section_type: OTHER
    supporting_text: |-
      the response regulator **MxbM** is described as **required for expression of the mxa operon**, alongside MxcQE and MxaB
  - reference_section_type: OTHER
    supporting_text: |-
      the **MxbDM two-component system is required for repression of the xox1 operon in the absence of lanthanides**; the Skovran review further emphasizes that **MxbM is uniquely required for repression of xox1** in the described network
  - reference_section_type: OTHER
    supporting_text: |-
      **MxbD/MxbM** is best supported as a **regulatory (signaling) module**, not a metabolic enzyme: it is a two-component system required for proper expression and reciprocal control of methanol dehydrogenase gene clusters
  - reference_section_type: OTHER
    supporting_text: |-
      it is not known if the requirement for these regulators is direct or indirect or what is being sensed by these systems
  - reference_section_type: OTHER
    supporting_text: |-
      neither the phosphorylation state nor direct DNA binding by these response regulators has been shown
  - reference_section_type: OTHER
    supporting_text: |-
      it is expected to function at the **cell envelope–cytosol signaling interface**, but **experimental validation of membrane topology/localization in AM1 is lacking** in the evidence retrieved here
  - reference_section_type: OTHER
    supporting_text: |-
      The authors fused the **“methanol-sensing domain” of MxbD** (from *M. extorquens*) with the transmitter domain of *E. coli* EnvZ to create a chimeric histidine kinase (MxbDZ)
status: COMPLETE