mxcE encodes the response regulator component of the MxcQE two-component regulatory system, functioning as a DNA-binding transcriptional activator positioned at the apex of the methanol dehydrogenase regulatory cascade. The protein contains a conserved N-terminal receiver domain with a characteristic (Ξ±Ξ²)β fold that receives phosphoryl groups from the MxcQ sensor kinase on a conserved aspartate residue (Asp71 per UniProt), and a C-terminal LuxR-type winged helix-turn-helix DNA-binding domain. Upon phosphorylation, MxcE activity is modulated to promote DNA binding by its C-terminal effector domain, enabling it to activate expression from the mxbDM promoter and thereby control transcription of the second-tier two-component system MxbDM. This hierarchical regulatory architecture (MxcQE then MxbDM then mxa operon) integrates environmental signals, including the lanthanide-dependent switch between the Ca-dependent (mxa) and lanthanide-dependent (xox1) methanol dehydrogenase systems, to control methanol oxidation capacity. MxcE is required for methanol metabolism, since cell-free extracts from mxcE mutant strains show zero or reduced binding activity towards the mxaF promoter, and mxcE mutants exhibit altered transcription of methylotrophy genes.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000160 phosphorelay signal transduction system | IEA GO_REF:0000002 | ACCEPT | Summary: Correct - MxcE is the response regulator of the MxcQE two-component system, receiving phosphoryl groups from the MxcQ sensor kinase on a conserved aspartate in its N-terminal receiver domain and modulating downstream transcription. This is well supported by both domain architecture (UniProt Response regulatory domain 21-138; 4-aspartylphosphate at residue 71) and the literature. Supporting Evidence: file:METEA/mxcE/mxcE-claude-deep-research.md the mxcE gene encoding the response regulator component that translates phosphorylation signals from the MxcQ sensor kinase into transcriptional activation file:METEA/mxcE/mxcE-deep-research-falcon.md the phosphate is transferred to a cognate **response regulator** on a conserved aspartate in the N-terminal **receiver (REC) domain** |
| GO:0003677 DNA binding | IEA GO_REF:0000120 | ACCEPT | Summary: Correct - MxcE contains a C-terminal LuxR-type winged helix-turn-helix effector domain (UniProt HTH luxR-type domain 160-225) that mediates DNA binding. Mutational evidence shows that mxcE mutant extracts have reduced or zero binding to the mxaF promoter, and MxcE activates expression from the mxbDM promoter. While DNA binding is correct, the more specific molecular function is DNA-binding transcription activator activity (GO:0001216; see core_functions). Supporting Evidence: file:METEA/mxcE/mxcE-claude-deep-research.md a C-terminal effector domain with a winged helix-turn-helix fold that mediates DNA binding file:METEA/mxcE/mxcE-claude-deep-research.md cell-free extracts from mxcQ and mxcE mutant strains had zero or reduced binding activity towards the promoter fragments of the mxaF gene |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000002 | ACCEPT | Summary: Correct - MxcE functions as a transcriptional activator within the methanol-oxidation regulatory cascade. It activates expression from the mxbDM promoter, which in turn controls expression of the mxa (Ca-dependent methanol dehydrogenase) operon. mxcE mutants show altered transcriptional output at methylotrophy promoters. Supporting Evidence: file:METEA/mxcE/mxcE-claude-deep-research.md the effector domain functions as a DNA-binding transcriptional activator that recognizes specific promoter sequences and recruits RNA polymerase file:METEA/mxcE/mxcE-deep-research-falcon.md mutation of **mxcE** changes transcriptional outputs at specific promoters |
| GO:0001216 DNA-binding transcription activator activity | NAS | NEW | Summary: More specific molecular function than the generic GO:0003677 (DNA binding) IEA annotation. MxcE is a DNA-binding transcriptional activator whose C-terminal LuxR-type effector domain recognizes promoter sequences and recruits RNA polymerase; it activates expression from the mxbDM promoter, and mxcE mutant extracts lose binding to the mxaF promoter. Reason: Captures the precise transcription activator molecular function supported by the literature; refines the generic DNA binding term used in core_functions. Supporting Evidence: file:METEA/mxcE/mxcE-claude-deep-research.md the effector domain functions as a DNA-binding transcriptional activator that recognizes specific promoter sequences and recruits RNA polymerase |
| GO:0005737 cytoplasm | NAS | NEW | Summary: MxcE is a two-component response regulator and, like response regulators of this class, acts in the cytoplasm where it interacts with DNA and transcriptional machinery after phosphorylation. No direct localization experiment exists, so this is an inference consistent with response regulator biology (added to align core_functions with existing annotations). Reason: Core function localization term not present in existing_annotations; supported by response regulator biology. Supporting Evidence: file:METEA/mxcE/mxcE-deep-research-falcon.md response regulators in this class generally function in the **cytoplasm** |
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