Methyl-accepting chemotaxis protein

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MCPsignal
3zx6.png
Methyl-accepting chemotaxis protein I. PDB entry 3zx6[1]
Identifiers
Symbol MCPsignal
Pfam PF00015
Pfam clan CL0510
InterPro IPR004089
PROSITE PDOC00465
SCOP 1qu7
SUPERFAMILY 1qu7

Methyl-accepting chemotaxis protein (MCP) is a transmembrane sensor protein of bacteria. Use of the MCP allows bacteria to detect concentrations of molecules in the extracellular matrix so that the bacteria may smooth swim or tumble accordingly. If the bacteria detects rising levels of attractants (nutrients) or declining levels of repellents (toxins), the bacteria will continue swimming forward, or smooth swimming. If the bacteria detects declining levels of attractants or rising levels of repellents, the bacteria will tumble and re-orient itself in a new direction. In this manner, a bacteria may swim towards nutrients and away from toxins[2]

Environmental diversity gives rise to diversity in bacterial signalling receptors, and consequently there are many genes encoding MCPs.[3] 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).

Structure[edit]

MCPs share similar structure and signalling mechanism. MCPs form dimers. Three dimers of MCP are held together by CheY to form hexamers. Hexamers are held together by CheA to form lattices. MCPs either bind ligands directly or interact with ligand-binding proteins, transducing the signal to downstream signalling proteins in the cytoplasm. Most MCPs contain: (a) an N-terminal signal peptide that acts as a transmembrane alpha-helix in the mature protein; (b) a poorly-conserved periplasmic receptor (ligand-binding) domain; (c) a transmembrane alpha-helix; and (d) a highly-conserved C-terminal cytoplasmic domain that interacts with downstream signalling components. The C-terminal domain contains the methylated glutamate residues.

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.

Function[edit]

Binding a ligand causes a conformational change in the MCP receptor which translates down the hairpin structure. At the tip of the hairpin are two proteins that associate to the MCP: CheW and CheA. CheA acts as the sensor kinase. CheA has kinase activity and autophosphorylates itself on a histidyl residue with activated by the MCP. CheW is believed to be a transducer of the signal from the MCP to CheA. Phosphorylated CheA is active so it phosphorylates CheY, the activator response regulator. Phosphorylated CheY is active so it phosphorylates the basal body which is connected to the flagellum. Phosphorylation of the basal body acts as a flagellar switch and changes the direction of rotation of the flagellum. This change in direction allows for alternation between smooth swim and tumbling.

References[edit]

  1. ^ Ferris, H. U.; Zeth, K.; Hulko, M.; Dunin-Horkawicz, S.; Lupas, A. N. (2014). "Axial helix rotation as a mechanism for signal regulation inferred from the crystallographic analysis of the E. Coli serine chemoreceptor". Journal of Structural Biology. doi:10.1016/j.jsb.2014.03.015.  edit
  2. ^ Derr P, Boder E, Goulian M (February 2006). "Changing the specificity of a bacterial chemoreceptor". J. Mol. Biol. 355 (5): 923–32. doi:10.1016/j.jmb.2005.11.025. PMID 16359703. 
  3. ^ Alexander RP, Zhulin IB (February 2007). "Evolutionary genomics reveals conserved structural determinants of signaling and adaptation in microbial chemoreceptors". Proc. Natl. Acad. Sci. U.S.A. 104 (8): 2885–90. doi:10.1073/pnas.0609359104. PMC 1797150. PMID 17299051. 

External links[edit]

This article incorporates text from the public domain Pfam and InterPro IPR004089