The Signaling Pathway of a Bacterial Two-Component System Determined by cryo-EM

Abstract

Although two-component systems (TCSs) play ubiquitous roles in sensing signals for bacterial survival and virulence, a detailed structural map of the signal transduction pathway is lacking. Bacteriophytochromes (BphPs) are enzymatic photoreceptors with homologs in plants that regulate bacterial physiological responses via TCS signaling. Here, we employ cryo-EM to elucidate the structural basis of a light-regulated TCS by capturing the full-length BphP histidine kinase (HK) in complex with its downstream response regulator (RR). The RR binds as a dimer to the HK but contacts the enzyme only through one subunit. Light absorption perturbs the entire BphP structure, including the HK domain, which disrupts phosphorylation and phosphotransfer reactions and promote TCS complex dissociation. Thus, light controls signaling through both HK activity and reversible binding of the RR.