Structure and Dynamics of the Receptor:Kinase Complex that Mediates Bacterial Chemotaxis

Abstract

Bacterial chemotaxis, the ability of bacteria to adapt their motion to external stimuli, has long stood as a model system for understanding transmembrane signaling, intracellular information transfer, and motility. The sensory apparatus underlying chemotaxis displays remarkably sensitivity, robustness, and dynamic range. These properties stem from a highly cooperative excitation response and an integral feedback mechanism for adaptation to changing surroundings. Although the molecular components of the chemotaxis system are well characterized, we still do not fully understand the biophysical mechanisms responsible for function. This is because the sensory apparatus comprises an extensive multi-component transmembrane assembly of chemoreceptors, histidine kinases (CheA) and coupling proteins (CheW), whose architecture is just emerging. We will discuss efforts to understand the detailed structure of the chemoreceptor:CheA:CheW complex and how chemoreceptors transmit signals across the membrane to regulate CheA activity. To address these issues, studies have been undertaken on isolated components, reconstituted complexes, and native receptor arrays. Soluble, chemoreceptor maquettes that mimic receptor oligomeric states have been particularly useful for studying kinase activation. Evidence will be presented to support the notion that changes to both molecular structure and dynamics are involved in signal transduction by the receptor:kinase assemblies.