Insight into structural remodeling of the FlhA ring responsible for bacterial flagellar type III protein export
Naoya Terahara1,*, Yumi Inoue1,*, Noriyuki Kodera2, Yusuke V. Morimoto1,3,4, Takayuki Uchihashi2,5,6, Katsumi Imada7, Toshio Ando2,8, Keiichi Namba1,3,† and Tohru Minamino1,†
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Science Advances 25 Apr 2018: Vol. 4, no. 4, eaao7054
Abstract
The bacterial flagellum is a supramolecular motility machine. Flagellar assembly begins with the basal body, followed by the hook and finally the filament. A carboxyl-terminal cytoplasmic domain of FlhA (FlhAC) forms a nonameric ring structure in the flagellar type III protein export apparatus and coordinates flagellar protein export with assembly. However, the mechanism of this process remains unknown. We report that a flexible linker of FlhAC (FlhAL) is required not only for FlhAC ring formation but also for substrate specificity switching of the protein export apparatus from the hook protein to the filament protein upon completion of the hook structure. FlhAL was required for cooperative ring formation of FlhAC. Alanine substitutions of residues involved in FlhAC ring formation interfered with the substrate specificity switching, thereby inhibiting filament assembly at the hook tip. These observations lead us to propose a mechanistic model for export switching involving structural remodeling of FlhAC.
Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).
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