The Dynamic Structures of the Type IV Pilus

The fundamental type IVa pilus (T4aP)‐like architecture includes a retractable pilus fiber, a motor, an alignment subcomplex, and—in Gram‐negative bacteria—an outer membrane secretin pore (Fig. 1). The pilus is an extracellular polymer of pilins. Pilins subunits are stored in the inner membrane and the motor powers their polymerization (extension) and depolymerization (retraction) at the pilus base. The alignment subcomplex connects the …