Larger clusters typically localize at the cell poles, while selleck inhibitor Several smaller clusters are found along the cell body [19–21]. In these clusters, receptors are arranged in roughly hexagonal arrays that are

presumably formed by trimers of receptor homodimers [22–25], with different receptors able to form mixed trimers [26]. Clusters are further stabilized by the association of CheA and/or CheW [19, 20, 27–29]. Receptor clusters are important for signal processing in chemotaxis, whereby allosteric interactions between receptors within clusters allow amplification and integration of chemotactic signals [7, 30–33]. All other chemotaxis proteins – CheR, CheB, CheY and CheZ – localize to receptor clusters AZD2281 clinical trial in E. coli through association with either receptors (CheR) or CheA (CheZ and CheY) or both (CheB) [20, 34–36]. Receptor click here clustering plays therefore an additional role by providing a scaffold for chemotaxis signalling [2].

The relatively stable signal-processing core of these clusters is composed of receptors, CheA, CheW and a phosphatase CheZ, along with the dynamically exchanging adaptation enzymes and CheY [37]. Adaptation enzymes are believed to primarily localize to the clusters via association with the C-terminal pentapeptide sequence of major receptors Tar and Tsr [35, 36, 38–40], but they also bind to their substrate sites – unmethylated glutamates for CheR and glutamines or methylated glutamates for CheB – on the receptors. Moreover, CheB also binds to the P2 domain of CheA, competing for the binding site with CheY [40, 41]. The aim of this study was to investigate whether cluster stability in vivo is regulated by such physiologically relevant factors as adaptation to the chemotactic signals and by Methane monooxygenase the environmental temperature. Several biochemical

studies indicated that stability of sensory complexes might strongly increase with the level of receptor methylation [7, 42]. However, a more recent study reported extreme ultrastability of the biochemically reconstituted sensory complexes with no discernible effect of receptor modification under the reference conditions [43], although complexes formed by the less modified receptors did show higher susceptibility to destabilizing agents. Surprisingly, this later study also reported a dramatic reduction of the complex stability at temperatures above 30°C. By performing an in vivo analysis of cluster stability using fluorescence recovery after photobleaching (FRAP), we were able to reconcile these apparently conflicting biochemical studies by showing that the exchange of CheA and CheW at receptor clusters is weakly dependent on the receptor modification.