Figure 1. Filament labeling convention, depiction of pilin domains, and GC-T4P symmetries.

(A) GC-T4P filament colored by 3-start helix (left) and 4-start helix (right). Black arrow indicates 1-start direction, white arrow indicates 3-start direction (left). Red arrow indicates 4-start direction (right). (B) GC-T4P filament. Pulled and fixed subunits (gray), “bulk” subunits (colored). (C) A single subunit colored by domain; the globular head domain (red) and α1 domain (gray).