Abstract
The FliPQR complex constitutes a channel for export of the bacterial flagellar proteins involved in axial structure assembly. It also serves as a template for flagellar rod assembly. A periplasmic gate, formed by the N-terminal α-helices of FliP and FliR, remains closed until FliE assembles onto FliP and FliR. The mechanism by which FliE opens the gate and assembles has remained unclear. Here, we present a cryoEM structure of the FliPQR complex in closed form at 3.0 Å resolution. A β-cap formed by the N-terminal β-strands of FliP and FliR creates a tight seal in the closed gate. Interaction of FliE with FliP and FliR induces a conformational change in FliP and FliR, with their N-terminal α-helices move up and outward. Consequently, the N-terminal β-strands of FliP and FliR start opening the periplasmic gate one after another and form a docking site for FliE to initiate rod assembly.
Competing Interest Statement
The authors have declared no competing interest.
