6D8V

Methyl-accepting Chemotaxis protein X

Summary for 6D8V

• Entry DOI: 10.2210/pdb6d8v/pdb
• Descriptor: Probable chemoreceptor (Methyl-accepting chemotaxis) transmembrane protein, 2-AMINO-2-HYDROXYMETHYL-PROPANE-1,3-DIOL, 1,1-DIMETHYL-PROLINIUM, ... (4 entities in total)
• Functional Keywords: mcp, chemotaxis, membrane protein
• Biological source: Rhizobium meliloti (strain 1021) (Ensifer meliloti)
• Total number of polymer chains: 1
• Total formula weight: 28984.43

Authors

Shrestha, M.,Schubot, F.D. (deposition date: 2018-04-27, release date: 2019-04-17, Last modification date: 2024-03-13)

Primary citation

Shrestha, M.,Compton, K.K.,Mancl, J.M.,Webb, B.A.,Brown, A.M.,Scharf, B.E.,Schubot, F.D.
Structure of the sensory domain of McpX fromSinorhizobium meliloti, the first known bacterial chemotactic sensor for quaternary ammonium compounds.
Biochem. J., 475:3949-3962, 2018

PubMed Abstract: The α-proteobacterium can live freely in the soil or engage in a symbiosis with its legume host. facilitates nitrogen fixation in root nodules, thus providing pivotal, utilizable nitrogen to the host. The organism has eight chemoreceptors, namely McpT to McpZ and IcpA that facilitate chemotaxis. McpX is the first known bacterial sensor of quaternary ammonium compounds (QACs) such as choline and betaines. Because QACs are exuded at chemotaxis-relevant concentrations by germinating alfalfa seeds, McpX has been proposed to contribute to host-specific chemotaxis. We have determined the crystal structure of the McpX periplasmic region (McpX) in complex with the proline betaine at 2.7 Å resolution. In the crystal, the protein forms a symmetric dimer with one proline betaine molecule bound to each monomer of McpX within membrane-distal CACHE module. The ligand is bound through cation-πinteractions with four aromatic amino acid residues. Mutational analysis in conjunction with binding studies revealed that a conserved aspartate residue is pivotal for ligand binding. We discovered that, in a striking example of convergent evolution, the ligand-binding site of McpX resembles that of a group of structurally unrelated betaine-binding proteins including ProX and OpuAC. Through this comparison and docking studies, we rationalized the specificity of McpX for this specific group of ligands. Collectively, our structural, biochemical, and molecular docking data have revealed the molecular determinants in McpX that are crucial for its rare ligand specificity for QACs.

PubMed: 30442721
DOI: 10.1042/BCJ20180769

Experimental method

X-RAY DIFFRACTION (2.8 Å)