Figure 4.

Archaic pilin assembly is accompanied by folding of two segments in the pilin. A, structural superposition of CsuC-bound CsuA/B (green) and CsuA/Bsc (magenta). B, cartoon diagram of CsuA/Bsc highlighting regions that do not significantly change (green), change dramatically (yellow), and undergo unfolded-folded transition (violet) during assembly. Two sites undergoing dramatic changes upon DSE are framed in rectangles. Phe-30 and Val-50 are shown as ball-and-sticks. C, steric clashes with CsuC prevent formation of A′–A″ and B–B′ hairpins in CsuC-bound CsuA/B subunit. Close up of the superposition shown in A (ribbon representation, stereo view). Donor strands G₁ and Gd are shown as cartoon diagrams and colored blue and yellow, respectively. Phe-30 and Val-50 in CsuA/B and donor residues in G₁ of CsuC are shown as ball-and-sticks and labeled. D, schematic of the mechanism of the archaic assembly.