Metal detoxification is essential for bacteria’s survival in adverse environments and their pathogenesis in hosts. Understanding the underlying mechanisms is crucial for devising antibacterial treatments. In the Gram-negative bacteriumEscherichia coli, membrane-bound sensor CusS and its response regulator CusR together regulate the transcription of thecusoperon that plays important roles in cells’ resistance to copper/silver, and they belong to the two-component systems (TCSs) that are ubiquitous across various organisms and regulate diverse cellular functions. In vitro protein reconstitution and associated biochemical/physical studies have provided significant insights into the functions and mechanisms of CusS–CusR and related TCSs. Such studies are challenging regarding multidomain membrane proteins like CusS and also lack the physiological environment, particularly the native spatial context of proteins inside a cell. Here, we use stroboscopic single-molecule imaging and tracking to probe the dynamic behaviors of both CusS and CusR in live cells, in combination with protein- or residue-specific genetic manipulations. We find that copper stress leads to a cellular protein concentration increase and a concurrent mobilization of CusS out of clustered states in the membrane. We show that the mobilized CusS has significant interactions with CusR for signal transduction and that CusS’s affinity toward CusR switches on upon sensing copper at the interfacial metal-binding sites in CusS’s periplasmic sensor domains, prior to ATP binding and autophosphorylation at CusS’s cytoplasmic kinase domain(s). The observed CusS mobilization upon stimulation and its surprisingly early interaction with CusR likely ensure an efficient signal transduction by providing proper conformation and avoiding futile cross talks.

The Wagner-Jauregg reaction, despite its potential utility, has remained largely unexplored since its discovery in 1930. Utilizing density functional theory (DFT) calculations and experimental 1 H nuclear magnetic resonance (NMR) kinetics data to generate a Hammett plot, the reaction is shown to proceed via a highly asynchronous, concerted mechanism, analogous to the Diels-Alder reaction. Our development of milder, more reliable reaction conditions for the Wagner-Jauregg reaction will facilitate the synthesis of novel, structurally complex, polycyclic molecules.