methyl accepting chemotaxis protein complex

GO:0098561 · Other · Subcellular region · Proposed

The chemoreceptor array: a hexagonal lattice of trimers-of-dimers of methyl-accepting chemotaxis proteins, held at the membrane by the CheA kinase and the CheW coupling protein. The array is the cell's sensory organ, and its geometry — a 12 nm hexagonal spacing conserved across bacteria and archaea — is what gives chemotaxis its cooperativity and gain. [DOI:10.1073/pnas.0905181106]

Synonyms: chemoreceptor array; chemosensory array

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Genes	Stoichiometry	Essential	Role
methyl-accepting chemotaxis proteins	Protein	part of	tar, tsr, trg, tap	trimers of dimers at each lattice vertex	ESSENTIAL	Bind ligands and transmit the signal down a long coiled-coil to the kinase; methylation of their helices sets adaptation. `DOI:10.1073/pnas.0905181106` Briegel et al. 2009 resolve the trimer-of-dimers lattice across many species.
histidine kinase CheA	Protein	part of	cheA		ESSENTIAL	The output kinase; its autophosphorylation is what receptor occupancy modulates. `DOI:10.1073/pnas.0905181106` Briegel et al. 2009 place CheA in the baseplate beneath the receptor lattice.
coupling protein CheW	Protein	part of	cheW		ESSENTIAL	Couples receptors to the kinase and, with CheA, forms the rings that hold the hexagonal geometry. `DOI:10.1073/pnas.0905181106` Briegel et al. 2009 describe the CheA/CheW baseplate defining the 12 nm spacing.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

methyl-accepting chemotaxis proteins

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P07017`	Methyl-accepting chemotaxis protein II	tar	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene tar in Escherichia coli K-12, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `PMID:22380631` Li G et al. 2012, ‘Isolation and identification of new inner membrane-associated proteins that localize to cell poles in Escherichia coli.’, Mol Microbiol. ECO:0000269 experimental evidence cited by UniProt for the 'Cell inner membrane' localisation of P07017.
`UniProtKB:P02942`	Methyl-accepting chemotaxis protein I	tsr	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (2 references) The single reviewed UniProtKB entry for gene tsr in Escherichia coli K-12, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `PMID:15919996` Daley DO et al. 2005, ‘Global topology analysis of the Escherichia coli inner membrane proteome.’, Science. ECO:0000269 experimental evidence cited by UniProt for the 'Cell inner membrane' localisation of P02942. `PMID:22380631` Li G et al. 2012, ‘Isolation and identification of new inner membrane-associated proteins that localize to cell poles in Escherichia coli.’, Mol Microbiol. ECO:0000269 experimental evidence cited by UniProt for the 'Cell inner membrane' localisation of P02942.
`UniProtKB:P05704`	Methyl-accepting chemotaxis protein III	trg	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (2 references) The single reviewed UniProtKB entry for gene trg in Escherichia coli K-12, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `PMID:15919996` Daley DO et al. 2005, ‘Global topology analysis of the Escherichia coli inner membrane proteome.’, Science. ECO:0000269 experimental evidence cited by UniProt for the 'Cell inner membrane' localisation of P05704. `PMID:22380631` Li G et al. 2012, ‘Isolation and identification of new inner membrane-associated proteins that localize to cell poles in Escherichia coli.’, Mol Microbiol. ECO:0000269 experimental evidence cited by UniProt for the 'Cell inner membrane' localisation of P05704.
`UniProtKB:P07018`	Methyl-accepting chemotaxis protein IV	tap	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene tap in Escherichia coli K-12, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `PMID:22380631` Li G et al. 2012, ‘Isolation and identification of new inner membrane-associated proteins that localize to cell poles in Escherichia coli.’, Mol Microbiol. ECO:0000269 experimental evidence cited by UniProt for the 'Cell inner membrane' localisation of P07018.

histidine kinase CheA

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P07363`	Chemotaxis protein CheA	cheA	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene cheA in Escherichia coli K-12, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `https://www.uniprot.org/uniprotkb/P07363` UniProtKB reviewed (Swiss-Prot) entry P07363, the single reviewed entry for gene cheA in Escherichia coli K-12. Establishes the accession and gene identity only; the component's membership in this structure rests on the record's own sources.

coupling protein CheW

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0A964`	Chemotaxis protein CheW	cheW	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene cheW in Escherichia coli K-12, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `https://www.uniprot.org/uniprotkb/P0A964` UniProtKB reviewed (Swiss-Prot) entry P0A964, the single reviewed entry for gene cheW in Escherichia coli K-12. Establishes the accession and gene identity only; the component's membership in this structure rests on the record's own sources.

Taxonomic distribution

NCBITaxon:2 Bacteria — COMMON: Found wherever chemotaxis is; the lattice geometry is conserved even between distant lineages. [DOI:10.1073/pnas.0905181106]
NCBITaxon:2157 Archaea — VARIABLE: Archaeal chemotaxis uses the same array architecture, coupled to the archaellum instead of a flagellum. [DOI:10.1073/pnas.0905181106]

Canonical examples

NCBITaxon:83333 Escherichia coli K-12 — The reference chemotaxis system. [DOI:10.1073/pnas.0905181106]

Functions

chemotaxis GO:0006935 — Converts occupancy of receptor binding sites into a change in CheA autophosphorylation, and so into flagellar switching.
- DOI:10.1073/pnas.0905181106 Briegel et al. 2009 relate array architecture to chemotactic signalling.
- DOI:10.1146/annurev-biophys-070816-033555 The cryotomography review (2017) uses the chemoreceptor array as its worked example of structure resolved in situ.

Associated traits

MODULATES METPO:1000702 motile
- DOI:10.1073/pnas.0905181106 Briegel et al. 2009 describe the array as the input to the flagellar switch; TraitMech records motility as METPO:1000702.

Physical properties

OTHER: ~12 UO:0000018 (hexagonal lattice spacing, conserved across bacteria and archaea) [DOI:10.1073/pnas.0905181106]

Mechanism graphs

CheA and CheW network receptor trimers into a hexagonal array (ASSEMBLY)

Methyl-accepting chemotaxis proteins assemble as receptor trimers of dimers. CheA dimers and CheW couplers connect neighboring trimers through a baseplate of alternating CheA regulatory domains and CheW subunits, yielding the extended hexagonal array that supports cooperative chemotaxis signalling.

Subject	Predicate	Object	Evidence
methyl-accepting chemotaxis protein	oligomerizes into	MCP trimer of dimers	`DOI:10.1073/pnas.1115719109` Briegel et al. 2012 combined crystallography with cryo-electron tomography of native arrays to place receptor trimers of dimers at hexagonal lattice vertices.
CheA histidine kinase dimer	bridges	MCP trimer of dimers	`DOI:10.1073/pnas.1104824108` Li and Hazelbauer 2011 showed that purified core signaling complexes contained two receptor trimers of dimers and two CheW proteins for each CheA dimer.
CheW coupling protein	couples	MCP trimer of dimers	`DOI:10.1073/pnas.1104824108` Li and Hazelbauer 2011 established the two-CheW stoichiometry of the two-trimer, one-CheA-dimer core unit.
MCP trimer of dimers	combines with	alternating CheA/CheW baseplate ring	`DOI:10.1073/pnas.1115719109` Briegel et al. 2012 modeled the receptor trimers surrounding alternating CheA/CheW rings in the cytoplasmic baseplate.
alternating CheA/CheW baseplate ring	forms	chemoreceptor core signaling unit	`DOI:10.1021/bi5000614` Briegel, Li, Bilwes, Hughes, Jensen and Crane 2014 reviewed a sequential assembly model in which two receptor trimers, one CheA dimer, and two CheW monomers form the core functional unit before hexagons and the superlattice.
chemoreceptor core signaling unit	tiles into	methyl accepting chemotaxis protein complex	`DOI:10.1073/pnas.0905181106` Briegel et al. 2009 found a conserved hexagonal lattice spacing of about 12 nm in chemoreceptor arrays from diverse bacteria and archaea. `DOI:10.1073/pnas.1115719109` Briegel et al. 2012 showed that CheA dimerization domains link neighboring rings to form the extended stable array.

Chemoeffector binding is amplified by the array and read out as phospho-CheY (FUNCTION)

The array's function is gain: binding at one receptor reaches ~35 kinases, and the cluster's output is a phospho-CheY signal the flagellar motor reads. The edges stop where the cited source stops -- the CheA-to-CheY phosphotransfer step itself is not stated quotably here, and motor switching is a trait rather than part of this structure.

Subject	Predicate	Object	Evidence
CheW coupling protein	couples	CheA histidine autokinase	`DOI:10.1016/j.tim.2015.03.003` — Chemoreceptors form stable core signaling complexes with two cytoplasmic proteins, CheA, a histidine autokinase, and CheW, which couples CheA to receptor control. Verbatim from the open-access full text (PMC4417406).
attractant chemoeffector	regulates	CheA histidine autokinase	`DOI:10.1016/j.tim.2015.03.003` — In the chemosensory array, attractant binding to a single receptor can regulate ~35 CheA kinase proteins [ 82 ]. Verbatim. The ~35:1 ratio is the quantitative statement of why the array is a structure rather than a collection of receptors.
methyl-accepting chemotaxis protein	modulates	CheA autophosphorylation	`DOI:10.1016/j.tim.2015.03.003` — MCP signaling complexes modulate CheA autophosphorylation activity over more than a 100-fold range, most likely through changes in receptor conformation or dynamic motions that allosterically regulate P1-P4' interactions and/or the kinase active site. Verbatim. The authors hedge the mechanism with 'most likely'; the 100-fold modulation itself is reported without hedge.
methyl accepting chemotaxis protein complex	amplifies	CheA autophosphorylation	`DOI:10.1016/j.tim.2015.03.003` — These receptors operate in cooperative arrays to produce large changes in the activity of a signaling kinase CheA in response to small changes in chemoeffector concentration. Verbatim from PMC4417406.
methyl accepting chemotaxis protein complex	produces	phospho-CheY	`DOI:10.1016/j.tim.2015.03.003` — These observations imply that a cell’s receptor cluster produces phospho-CheY signals in a pulsatile manner, consistent with essentially all-ON or all-OFF array behavior. Verbatim. Stated as an implication of the observations, not a direct measurement, and the edge is no stronger than that. The CheA-to-CheY phosphotransfer step is not stated quotably in this source, so it is not drawn as an edge.
CheA histidine autokinase	transfers phosphoryl group to	phospho-CheY	`DOI:10.1021/bi962261k` Stewart 1997 kinetically characterized CheA-to-CheY phosphotransfer as reversible CheY binding to phospho-CheA followed by rapid reversible phosphoryl transfer.
phospho-CheY	signals	flagellar motor reversal to clockwise rotation	`DOI:10.1016/j.tim.2015.03.003` — The motor that was closer to the cell’s receptor cluster reversed first, followed by the second motor with a time lag determined by its distance from the first motor and consistent with the intracellular diffusion rate of phospho-CheY, the CW rotational signal. Verbatim. Motor reversal is included as the readout of this structure's output, not as part of the structure; the motility phenotype itself is the METPO:1000702 trait link.

Discussions

CURATION_TODO (RESOLVED): The CheA-to-CheY phosphotransfer step is missing from the signalling graph because Parkinson et al. 2015 does not state it in a quotable sentence. Should a primary source for the phosphotransfer be added, or is the array's output adequately described by 'the receptor cluster produces phospho-CheY signals'? The graph deliberately stops where the source stops. Drawing the step from background knowledge would be the defect #161 records.

Evidence

DOI:10.1073/pnas.0905181106 Briegel A et al. 2009, 'Universal architecture of bacterial chemoreceptor arrays', PNAS.
DOI:10.1146/annurev-biophys-070816-033555 'Progress and Potential of Electron Cryotomography as Illustrated by Its Application to Bacterial Chemoreceptor Arrays', Annual Review of Biophysics 2017.

Curation history

2026-09-02T04:49:54Z claude · CREATED_RECORD — Drafted from the cited reviews; every GO term, taxon id and DOI resolved live before writing. Not yet human-reviewed.
2026-09-03T00:15:13Z claude · ADD_CAUSAL_GRAPH — #163: added the array signalling graph. The record's two existing sources could not support it -- Briegel et al. 2009 is a cryo-ET architecture paper and the Annual Review is abstract-only -- so Parkinson, Hazelbauer & Falke 2015 (PMC4417406) was added, whose full text is open. Six edges, each with a verbatim quotation. The CheA-to-CheY phosphotransfer step is not drawn because the source does not state it quotably; a discussion records that.
2026-09-03T00:19:39Z claude · CORRECT_NODE_LABEL — CI's id-label gate refused the array node: it was labelled 'chemosensory array' while its grounding GO:0098561 is 'methyl accepting chemotaxis protein complex'. The informal name came from the source's prose. Relabelled to the canonical term rather than added to conf/id_label_targets.yaml, because there is no curation reason to differ -- the exception list is for residuals a curator has accepted, not for making a gate quiet.
2026-09-04T04:32:00Z codex · ENHANCE_CAUSAL_GRAPH — Added a CheA/CheW ASSEMBLY graph for hexagonal array formation, anchored MCP and CheW graph nodes with Pfam identifiers, added a directly cited CheA-to-CheY phosphotransfer edge, and resolved the phosphotransfer curation TODO.
2026-09-08T07:40:05Z uniprot_genes · SEED_PROTEIN_EXAMPLES — #183: added 6 protein example(s) by resolving each of the component's declared gene symbols to the single reviewed UniProtKB entry for that symbol in a taxon this record names, deduplicated by accession. Symbols resolving to more than one reviewed entry were skipped rather than chosen between.

Source: data/structures/other/methyl_accepting_chemotaxis_protein_complex.yaml