Piston power

Abstract

Chemotactic signal transduction allows bacterial cells to modify their motility in response to chemical stimuli, facilitating movement towards attractants and away from repellents. The mechanism involved in this signal transduction process has long remained elusive. Fundamentally, ligands are first bound at the periplasmic face of transmembrane receptors, which then induces a conformational change that is transmitted to the cytoplasmic domain of the receptor. Signaling from the cytoplasmic domain ultimately regulates the direction of flagellar rotation. Ottemann et al. 1 Ottemann K.M. et al. A piston model for transmembrane signaling of the aspartate receptor. Science. 1999; 285: 1751-1754 Crossref PubMed Scopus (235) Google Scholar placed spin labels at strategic positions in the aspartate receptor to distinguish between some of the various models proposed for transmembrane signaling. Electron paramagnetic resonance spectroscopy was used to show that one of the pair of transmembrane helices in the receptor moves downwards, in a piston-like fashion, when the ligand is bound. The movement involved was very small (∼1Å). Therefore, the receptor-associated proteins, CheW and CheA, must be capable of detecting small changes in receptor conformation. This mechanism of transmembrane signaling might be applicable to a larger class of receptor proteins.