Schematic of receptor clustering in E. coli.

(A) Association and dissociation of adapter protein CheW and kinase CheA2 with the complexes. CheW interacts directly with the receptors, but the interaction of CheA with the receptors is largely mediated by CheW (see below). (B) Electron cryotomography images show that trimers of dimers (TDs) of chemoreceptors cluster at the cell poles in a hexagonal manner [28–31]. (C) Nanodisc experiments propose that two TDs are connected by a linker consisting of two CheW monomers and one CheA2 dimer [9]. In reality, the P5 domain of CheA may also contact the trimer [21, 31, 32], although this binding may be an order of magnitude weaker than CheW-trimer binding [9, 29]. (D) Top view of an ensemble of different sizes of receptor complexes in the cytoplasmic membrane. Active receptors are shown in red, and inactive receptors are shown in blue. Each linker between active TDs contributes a coupling energy J.