Fig. 4.

Axial view of adjacent subunits i and i + 5: adapted from a portion of Fig. 1a of Ref. 10. Only the three α-helices of the flagellin moiety that builds the outer tube are shown, as spirals passing through the α-carbon atoms. The circular arcs mark the reference cylinder of radius 45 Å. The long α-helix CD1 (cf. Fig. 3)—drawn here with a thicker line—appears more or less straight in this view, with its upper (distal) end at larger radius: locations p, c and d (cf. Fig. 3) are marked. The α-helix ND1a “wraps around” CD1 in this view: its upper end is at larger radius, and points e, a, b and q are marked. Helix ND1b, which is practically axial, appears as a small circle in this view. The bi-stable interface between ab and cd is marked by five lines, somewhat as in Fig. 3: observe that portion ab of ND1a appears to be straight in this view. (a) L filament, (b) R filament.