Structural insights from electron cryotomography.

(A) Our linker –CheW–CheA2–CheW– based on nanodisc experiments (black line) [9] appears to be more complicated in reality, where the P5 domain of CheA (homologous to CheW) may also contact the trimers of dimers directly (contact 1 in red) [21, 31, 32]. Such an alternative linker, defined as =CheW/CheA2/CheW= is explored in S4 Fig. However, the binding of CheW to the trimers (contact 2 in orange) is presumably much stronger (see Fig. 5A,B in [9] and discussion in [29]), rendering CheA2 effectively a bridging molecule. (B) Hexagonally packed trimer-of-dimers structure in which the inner connecting ring is formed by alternating CheW/CheA (P5) units [28–31, 52].