Genetic Analysis of the Salmonella FliE Protein That Forms the Base of the Flagellar Axial Structure
Jordan J. Hendriksen, Hee Jung Lee, Alexander J. Bradshaw, Keiichi Namba, Fabienne F. V. Chevance, Tohru Minamino, Kelly T. Hughes
Abstract
The bacterial flagellum represents one of biology's most complex molecular machines. Its rotary motor spins at speeds of more than 2,000 cycles per second, and its type 3 secretion (T3S) system secretes proteins at rates of tens of thousands of amino acids per second. Within the complex flagellar motility machine resides a unique protein, FliE, which serves as an adaptor to connect a planar, inner membrane-embedded ring structure, the MS-ring, the core T3S secretion complex at the cytoplasmic base, and a rigid, axial structure that spans the periplasmic space, penetrates the outer membrane, and extends 10 to 20 microns from the cell surface. This work combines genetic mutant suppressor analysis with the structural data for the core T3S system, the MS-ring, and the axial drive shaft (rod) that transverses the periplasm to provide insight into the essential adaptor role of FliE in flagellum assembly and function.