Comparison of flagellar FlhBC and its paralogues from the needle type III secretion system. (a) Multiple sequence alignment of FlhBC from S. typhimurium (SalFlhBC; Swiss-Prot accession No. P40727) with FlhBC from A. aeolicus (AquFlhBC; O67813), EscUC from E. coli (Q7DB59), YscUC from Yersinia pestis (P69986), SpaSC from S. typhimurium (P40702) and Spa40C from Shigella flexneri (Q6XVW1). Identical residues are boxed in red; similar residues are coloured red. Alignment was performed with ClustalW (Larkin et al., 2007 ▶; Goujon et al., 2010 ▶). (b) Stereoviews of the superposition of Salmonella FlhBC (blue; PDB entry 3b0z; this work), Aquifex FlhBC (red; PDB entry 3b1s; this work), EscUC (orange; PDB entry 3bzo; Zarivach et al., 2008 ▶), YscUC (grey; PDB entry 2jli; Lountos et al., 2009 ▶), SpaSC (green; PDB entry 3c01; Zarivach et al., 2008 ▶) and Spa40C (purple; PDB entry 2vt1; Deane et al., 2008 ▶).