TRANSMEMBRANE SIGNALING CHARACTERIZED IN BACTERIAL CHEMORECEPTORS BY USING SULFHYDRYL CROSS-LINKING IN-VIVO

Transmembrane signaling by bacterial chemoreceptors is thought to invo lve conformational changes within a stable homodimer. We investigated the functional consequences of constraining movement between pairs of helices in the four-helix structure of the transmembrane domain of che moreceptor Trg. Using a family of cysteine-containing receptors, we id entified oxidation treatments for intact cells that catalyzed essentia lly complete sulfhydryl cross-linking at selected positions and yet le ft flagellar and sensory functions largely unperturbed. Constraining m ovement by cross-links between subunits had little effect on tactic re sponse, but constraining movement between transmembrane segments of th e monomer drastically reduced function. We deduce that transmembrane s ignaling requires substantial movement between transmembrane helices o f a monomer but not between interacting helices across the interface b etween subunits.