Fig. 2: The CCW pose of the switch.
From: CryoEM structures reveal how the bacterial flagellum rotates and switches direction
In the global views, FliF is blue, FliG is red, FliM is yellow and FliN is pink and purple. In the insets of a–e, each of the subunits is coloured from the N-terminus (blue) to C-terminus (red) to highlight the fold. a, FliFC wraps around FliGD1. b, A FliG protomer folds into five domains: FliGD1 (FliG1–67), FliGD2 (FliG73–99), FliGD3 (FliG107–186), FliGD4 (FliG196–233) and FliGD5 (FliG243–331). c, The FliM subunit, highlighting FliML1 (FliM31–50), FliMmid (FliM51–230), FliML2 (FliM231–256) and FliMC (FliM257–330). d, A 180° rotated view of panel (c). e, Three FliNC subunits are similar but non-equivalent. To highlight the fold, only one protomer (FliN3) is coloured from the N-terminus (blue) to C-terminus (red). The remaining two (FliN1 and FliN2) are coloured pink and purple. f, A side view of a single FliFGMN unit. An ~30 Å cleft between FliFC–FliGD1/D2 and FliGD5 is highlighted. g, A single FliFGMN unit participates in three staves. h, Density for FliGD5 appears to be separated, with the domain having little contact with adjacent subunits. i, Interactions between the PAA motif of FliGD3 and the adjacent FliGL1 linker. j,k, Formation of a curved spiral by the FliMC:3FliNC heterotetramer. j, A schematic that compares the open ring of FliMC:3FliNC in the cryoEM structure to the closed ring of the crystal structure of T. maritima FliNC (1YAB42). This comparison highlights that a pure FliNC superstructure would favour stacked discs in a linear array. FliMC breaks the symmetry, which is necessary to form the helix along the bottom of the C-ring. k, The FliMC:3FliNC forms a spiral that curves along the base of the C-ring to form a closed circle. A single arc is shown.
