3atp | pdb_00003atp
Structure of the ligand binding domain of the bacterial serine chemoreceptor Tsr with ligand
Structural highlights
Function[MCP1_ECOLI] Receptor for the attractant L-serine and related amino acids. Is also responsible for chemotaxis away from a wide range of repellents, including leucine, indole, and weak acids. 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 PubMedEscherichia coli has closely related amino acid chemoreceptors with distinct ligand specificity: Tar for L-aspartate and Tsr for L-serine. Crystallography of the ligand-binding domain of Tar identified the residues interacting with aspartate, most of which are conserved in Tsr. However, swapping of the non-conserved residues between Tsr and Tar did not change ligand specificity. Analyses with chimeric receptors led us to hypothesize that distinct three-dimensional arrangements of the conserved ligand-binding residues are responsible for ligand specificity. To test this hypothesis, the structures of the apo and serine-binding forms of the ligand-binding domain of Tsr were determined at 1.95 and 2.5 A resolutions, respectively. Some of the Tsr residues are arranged differently from the corresponding aspartate-binding residues of Tar to form a high-affinity serine-binding pocket. The ligand-binding pocket of Tsr was surrounded by negatively charged residues, which presumably exclude negatively charged aspartate molecules. We propose that all these Tsr- and Tar-specific features contribute to specific recognition of serine and aspartate with the arrangement of the side chain of residue 68 (Asn in Tsr and Ser in Tar) being most critical. Ligand specificity determined by differentially arranged common ligand-binding residues in the bacterial amino acid chemoreceptors Tsr and Tar.,Tajima H, Imada K, Sakuma M, Hattori F, Nara T, Kamo N, Homma M, Kawagishi I J Biol Chem. 2011 Oct 6. PMID:21979954[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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