Ribbon representation of CheA (P1 – red, P2 – green, P3 – dark purple and grey, P4 – light pink and blue, P5 – magenta and light blue) and CheW (cyan) and Tm14 (yellow and orange) showing positions of residues mutated to Cys (yellow balls) and labeled with MTSSL for dipolar ESR or applied in disulfide cross-linking experiments. P1 and P2 are connected to P3, P4 and P5 by long unstructured linkers (dotted lines). For clarity, only one P1 and P2 domain is shown and spin-label sites are marked on only one CheA, CheW, and Tm14 subunit. CheW and P5 have related folds composed of two pseudosymmetric β-barrels known as subdomain 1 (SD1) and subdomain 2 (SD2).