Fig. 4.

The pseudopilus assembly model. (A) Electrostatic envelope of the pilus and PulG monomer, as calculated by APBS (31), inserted in the membrane (gray rectangle). Arrows indicate the PulG tethering via Asp⁴⁸–Arg⁸⁷ and Glu⁴⁴–Arg⁸⁸ salt bridges, the hydrophobic patch (outlined in green), and Glu⁵. (B) Ribbon view of the pilus and the incoming protomer, color-coded as in Fig.1. (C) The incoming protomer (P) incorporation is associated with the membrane extraction of the P₊₁, driven by the PulE ATPase, adding 10.4 Å to the pilus. (D and E) Zoom views of the rectangle in C showing two alternative interactions of Glu⁵ of P₊₃ with Phe¹ of P₊₄ (D) or Lys³⁵ and Lys²⁸ of P, stabilizing the pilus in its optimal state (E).