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From Proteopedia
Apo-Tar from E. coli
Structural highlights
Function[MCP2_ECOLI] Receptor for the attractant L-aspartate and related amino and dicarboxylic acids. Tar also mediates taxis to the attractant maltose via an interaction with the periplasmic maltose binding protein. Tar mediates taxis away from the repellents cobalt and nickel. Chemotactic-signal transducers respond to changes in the concentration of attractants and repellents in the environment, transduce a signal from the outside to the inside of the cell, and facilitate sensory adaptation through the variation of the level of methylation. Attractants increase the level of methylation while repellents decrease the level of methylation, the methyl groups are added by the methyltransferase CheR and removed by the methylesterase CheB. Publication Abstract from PubMedThe Escherichia coli cell-surface aspartate receptor Tar mediates bacterial chemotaxis toward an attractant, aspartate (Asp), and away from a repellent, Ni(2+). These signals are transmitted from the extracellular region of Tar to the cytoplasmic region via the transmembrane domain. The mechanism by which extracellular signals are transmitted into the cell through conformational changes in Tar is predicted to involve a piston displacement of one of the alpha4 helices of the homodimer. To understand the molecular mechanisms underlying the induction of Tar activity by an attractant, the three-dimensional structures of the E. coli Tar periplasmic domain with and without bound aspartate, Asp-Tar and apo-Tar, respectively, were determined. Of the two ligand-binding sites, only one site was occupied, and it clearly showed the electron density of an aspartate. The slight changes in conformation and the electrostatic surface potential around the aspartate-binding site were observed. In addition, the presence of an aspartate stabilized residues Phe-150' and Arg-73. A pistonlike displacement of helix alpha4b' was also induced by aspartate binding as predicted by the piston model. Taken together, these small changes might be related to the induction of Tar activity and might disturb binding of the second aspartate to the second binding site in E. coli. Structural Analysis of the Ligand-Binding Domain of the Aspartate Receptor Tar from Escherichia coli.,Mise T Biochemistry. 2016 Jul 5;55(26):3708-13. doi: 10.1021/acs.biochem.6b00160. Epub, 2016 Jun 20. PMID:27292793[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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