Figure 3: CryoEM reconstruction of the N. meningitidis T4P at 6 Å resolution.

(a) Side view of the Nm pilus cryoEM map showing the globular domain density and its connectivity in the right-handed 1-start helix (+1), the right-handed 4-start helix (+4) and the left-handed 3-start helix (−3). A single globular domain is outlined at the bottom of the map, with the ridge indicated with a thick dashed line and the central depression indicated with an arrow. (b) End view of a section of the cryoEM map showing the rod-like density corresponding to N-terminal α-helices. (c) Cross section of the Nm pilus reconstruction showing the rod-like α-helical density, the ends of which are connected near the central filament axis (red arrows). The full-length Ng PilE structure (2HI2) was fit as a rigid body into the globular domain density. The Pro22-induced kink results in the N-terminal α-helical segment completely missing the rod-like density. The rod-like density disappears just before it enters the globular domain density (red asterisks). (d) The Nm PilE structure was fit into the map in segments, as indicated. α1N was modelled from the corresponding region in the Ng PilE crystal structure, with the helix melted in α1:15–23, which straightens α1.