THREE-DIMENSIONAL STRUCTURES OF THE LIGAND-BINDING DOMAIN OF THE BACTERIAL ASPARTATE RECEPTOR WITH AND WITHOUT A LIGAND
[MCP2_SALTY] Receptor for the attractant L-aspartate and related amino and dicarboxylic acids. Tar mediates taxis away from the repellents cobalt and nickel. Unlike in E.coli tar, it does not mediates maltose taxis. 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 PubMed
The three-dimensional structure of an active, disulfide cross-linked dimer of the ligand-binding domain of the Salmonella typhimurium aspartate receptor and that of an aspartate complex have been determined by x-ray crystallographic methods at 2.4 and 2.0 angstrom (A) resolution, respectively. A single subunit is a four-alpha-helix bundle with two long amino-terminal and carboxyl-terminal helices and two shorter helices that form a cylinder 20 A in diameter and more than 70 A long. The two subunits in the disulfide-bonded dimer are related by a crystallographic twofold axis in the apo structure, but by a noncrystallographic twofold axis in the aspartate complex structure. The latter structure reveals that the ligand binding site is located more than 60 A from the presumed membrane surface and is at the interface of the two subunits. Aspartate binds between two alpha helices from one subunit and one alpha helix from the other in a highly charged pocket formed by three arginines. The comparison of the apo and aspartate complex structures shows only small structural changes in the individual subunits, except for one loop region that is disordered, but the subunits appear to change orientation relative to each other. The structures of the two forms of this protein provide a step toward understanding the mechanisms of transmembrane signaling.
Three-dimensional structures of the ligand-binding domain of the bacterial aspartate receptor with and without a ligand.,Milburn MV, Prive GG, Milligan DL, Scott WG, Yeh J, Jancarik J, Koshland DE Jr, Kim SH Science. 1991 Nov 29;254(5036):1342-7. PMID:1660187
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.