Fig. 3.

Cryo-EM structure of the V. cholerae toxin coregulated pilus (TCP). (A) Cryo-EM image, (B) 2D class average of V. cholerae TCP, (C) cryo-EM density map, TcpA model-to-map fit, helical model, and (D) vertical sectional view of density map of V. cholerae TCP. (E) Interaction between TCP subunits. Subunit:subunit interactions occur primarily between α1 helices. The S₀ subunit interacts mainly with subunit S₁, S₃, and S₄ and to a lesser extent with S₂. Total interface area between subunits calculated by PISA server are shown to the left of the connecting lines, and interaction interface area between the C-terminal domains (CTD) are shown in parentheses to the right. (F) Ribbon model of the core of the TCP filament with Met1 (yellow) and Glu5 shown in sphere representation using van der Waals radii. Glu5 of S₀ interacts with the amino-terminus of Met1 of the S₁ neutralizing two charges in a hydrophobic environment.