| Primary Identifier | IPR035440 | Type | Homologous_superfamily |
| Short Name | 4HB_MCP_dom_sf |
| description | This entry represents a four-helix bundle that operates as a ubiquitous sensory module in prokaryotic signal-transduction, which is known as four-helix bundles methyl-accepting chemotaxis protein (4HB_MCP) domain. The 4HB_MCP is always found between two predicted transmembrane helices indicating that it detects only extracellular signals. In many cases the domain is associated with a cytoplasmic HAMP domain suggesting that most proteins carrying the bundle might share the mechanism of transmembrane signalling which is well-characterised in E coli chemoreceptors [].Methyl-accepting chemotaxis proteins (MCPs) are a family of bacterial receptors that mediate chemotaxis to diverse signals, responding to changes in the concentration of attractants and repellents in the environment by altering swimming behaviour []. Environmental diversity gives rise to diversity in bacterial signalling receptors, and consequently there are many genes encoding MCPs []. For example, there are four well-characterised MCPs found in Escherichia coli: Tar (taxis towards aspartate and maltose, away from nickel and cobalt), Tsr (taxis towards serine, away from leucine, indole and weak acids), Trg (taxis towards galactose and ribose) and Tap (taxis towards dipeptides). MCPs share similar topology and signalling mechanisms. MCPs either bind ligands directly or interact with ligand-binding proteins, transducing the signal to downstream signalling proteins in the cytoplasm. MCPs undergo two covalent modifications: deamidation and reversible methylation at a number of glutamate residues. Attractants increase the level of methylation, while repellents decrease it. The methyl groups are added by the methyl-transferase cheR and are removed by the methylesterase cheB. Most MCPs are homodimers that contain the following organisation: an N-terminal signal sequence that acts as a transmembrane domain in the mature protein; a poorly-conserved periplasmic receptor (ligand-binding) domain; a second transmembrane domain; and a highly-conserved C-terminal cytoplasmic domain that interacts with downstream signalling components. The C-terminal domain contains the glycosylated glutamate residues. |
