The Structural Logic of Dynamic Signaling in the Escherichia coli Serine Chemoreceptor.

This study used in vivo protein crosslinking to follow stimulus-induced signals through Tsr, a bacterial transmembrane receptor for chemotaxis to serine. Our experiments distinguished Tsr conformations that activate or inhibit its signaling kinase partner and showed how those signals reach the receptor's kinase-controlling cytoplasmic tip. A dynamic junction in the Tsr molecule triggers stimulus responses by propagating a less stable helix-packing arrangement to flanking structural elements, thereby reducing structural stresses at the receptor tip. An AlphaFold model indicated that the dynamic junction might cause a structural distortion that destabilizes the receptor tip in the absence of a serine stimulus. This model and experimental approach could help to elucidate the signaling logic and mechanisms in other transmembrane chemoreceptor proteins.