Flagellar Hook/Needle Length Control and Secretion Control in Type III Secretion Systems.

Abstract

The flagellum is a motile organ, and the needle complex is a type III secretion apparatus for pathogenesis. There are more similarities than differences between the two structures at the molecular level. Here I focus on the hook and the needle and discuss their length control mechanism. The hook is a substructure of the flagellum and the needle is a part of the needle complex. Both structures are tubular structures that have a central channel for protein secretion. Their lengths are controlled by an intriguing mechanism involving a ruler protein and a switchable gate of the protein secretion system. A model for length control is proposed.