Chemoreceptor Trimers of Dimers and collaborative signaling teams

CLAUDIA A. STUDDERT; DIEGO A. MASSAZZA,; JOHN S. PARKINSON

Pinamar, Buenos Aires,

Congreso; XLI Reunión Anual Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB) (junto a PAABS Y SAN); 2005

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Bacteria detect chemical gradients and respond to them with extraordinary sensitivity. In E. coli, four transmembrane receptors with different specificities are mainly responsible for sensing attractant and repellent compounds and for signaling control commands to the flagellar motors through a cytoplasmic phosphorelay. These receptors (known as MCPs for methylaccepting chemotaxis proteins) possess a highly conserved cytoplasmic domain that interacts with a coupling protein (CheW) and a histidine kinase (CheA). Kinase activity is modulated by the receptors? ligand occupancy and methylation states. Although their native structure is a homodimer, the receptors form higher-order signaling complexes that cluster at the poles of the cell. Receptorreceptor interactions within the cluster have been implicated in signal amplification. Genetic and in vivo crosslinking studies indicate that the receptors are organized into mixed trimers of dimers in which receptors with different specificities collaboratively control their shared kinase molecules. We have used a cysteine-directed in vivo crosslinking approach to identify mutants in the serine receptor that are defective in trimerof- dimer formation. Here, we present results on the identification and functional characterization of trimer defective mutants that suggest that trimer formation is required for signaling.