A piston model for transmembrane signaling of the aspartate receptor

To characterize the mechanism by which receptors propagate conformational c hanges across membranes, nitroxide spin labels were attached at strategic p ositions in the bacterial aspartate receptor. By collecting the electron pa ramagnetic resonance spectra of these labeled receptors in the presence and absence of the Ligand aspartate, ligand binding was shown to generate an s imilar to 1 angstrom intrasubunit piston-type movement of one transmembrane helix downward relative to the other transmembrane helix. The receptor-ass ociated phosphorylation cascade proteins CheA and CheW did not alter the li gand-induced movement. Because the piston movement is very small, the abili ty of receptors to produce Large outcomes in response to stimuli is caused by the ability of the receptor-coupled enzymes to detect small changes in t he conformation of the receptor.