Figure 2.

EscC, PrgH and EscJ share a common fold for the assembly of the T3SS multi-ring basal body. (a) Ribbon representation of the EscC (21–174) crystal structure, highlighting the two domain fold and the connecting hinge region. (b) Ribbon representation of the EscJ crystal structure (pdb accession code 1yj7 ⁸). The top shows monomeric EscJ and the ring structure on the bottom illustrates the assembled 24mer oligomeric structure of EscJ, which has been previously described ⁸, ⁹. (c) Ribbon representation of the crystal structure of monomeric PrgH (170–362). (d) Superposition of both the outer membrane secretin EscC (21–174) (left panel) and the inner membrane protein PrgH (170–362) (right panel) to EscJ (pdb accession code 1yj7). Highlighted in orange and green are the conserved folds shared among the three proteins. The coloring scheme corresponds to the structures of EscC, EscJ and PrgH in panels (a) to (c). The schematic illustrates the integrated approach, based on the crystal structures and the observed conservation, of molecular modeling, experimental validation and docking into the EM density maps of the S. typhimurium basal body (EM accession codes emd_1224 and emd_1100) ⁵, ²¹. PrgH (170–362) was manually docked into the EM maps. The previously published EscJ structure and the EscC (21–174) models are automatically docked as described in the Methods.