MOLECULAR MECHANISM OF TRANSMEMBRANE SIGNALING BY THE ASPARTATE RECEPTOR - A MODEL

The aspartate receptor of bacterial chemotaxis is representative of a large class of membrane-spanning receptors found in prokaryotic and eu karyotic organisms. These receptors, which regulate histidine kinase p athways and possess two putative transmembrane helices per subunit, ap pear to control a wide variety of cellular processes. The best charact erized subgroup of the two helix receptor class is the homologous fami ly of chemosensory receptors from Escherichia coli and Salmonella typh imurium, including the aspartate receptor. This receptor binds asparta te, an attractant, in the periplasmic compartment and undergoes an int ramolecular, transmembrane conformational change, thereby modulating t he autophosphorylation rate of a bound histidine kinase in the cytopla sm. Here, we analyze recent results from x-ray crystallographic, solut ion F-19 NMR, and engineered disulfide studies probing the aspartate-i nduced structural change within the periplasmic and transmembrane regi ons of the receptor. Together, these approaches provide evidence that aspartate binding triggers a ''swinging-piston'' displacement of the s econd membrane-spanning helix, which is proposed to communicate the si gnal across the bilayer.