The structure of a soluble chemoreceptor suggests a mechanism for propagating conformational signals.
Publication Type:Journal Article
Source:Biochemistry, Volume 48, Issue 9, p.1936-44 (2009)
Keywords:Bacterial Proteins, Crystallography, X-Ray, Disulfides, Hydrogen Bonding, Membrane Proteins, Methyl-Accepting Chemotaxis Proteins, Models, Molecular, Protein Conformation, Protein Structure, Secondary, Recombinant Proteins, Signal Transduction, Thermotoga maritima
<p>Transmembrane chemoreceptors, also known as methyl-accepting chemotaxis proteins (MCPs), translate extracellular signals into intracellular responses in the bacterial chemotaxis system. MCP ligand binding domains control the activity of the CheA kinase, situated approximately 200 A away, across the cytoplasmic membrane. The 2.17 A resolution crystal structure of a Thermotoga maritima soluble receptor (Tm14) reveals distortions in its dimeric four-helix bundle that provide insight into the conformational states available to MCPs for propagating signals. A bulge in one helix generates asymmetry between subunits that displaces the kinase-interacting tip, which resides more than 100 A away. The maximum bundle distortion maps to the adaptation region of transmembrane MCPs where reversible methylation of acidic residues tunes receptor activity. Minor alterations in coiled-coil packing geometry translate the bulge distortion to a >25 A movement of the tip relative to the bundle stalks. The Tm14 structure discloses how alterations in local helical structure, which could be induced by changes in methylation state and/or by conformational signals from membrane proximal regions, can reposition a remote domain that interacts with the CheA kinase.</p>