Unit outline
News
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Research
Abstract
Motility is a very important function in the living world. For this purpose, organisms such as bacteria have developed the most incredible molecular machine: the flagellar system. Bacteria such as Escherichia coli and Salmonella typhimurium swim by rotating long helical filaments called the flagellum. The flagellum is a complex structure made by the association of many different proteins. It can be divided into three parts: 1) the filament: a long, rigid, tubular structure that works as a helical propeller, 2) the hook: a short, highly flexible tubular segment that works as a universal joint, and 3) the basal body: a rotary motor embedded in the cell membrane.
During the assembly of the flagellum, all the flagellar axial proteins are exported from the cytoplasm to the flagellum distal end through a 2 -3 nm channel located at its centre. This export mechanism is regulated by a specialized protein export system located on the cytoplasmic side of the basal body. It is called the Type III Export Apparatus and is found throughout the bacterial kingdom. In the case of Salmonella, this export apparatus is made by six membrane proteins: FlhA, FlhB, FliO, FliP, FliQ, FliR, and three cytoplasmic proteins: FliI, FliH and FliJ. The export apparatus of the bacterial flagellum is homolog to the type III secretion system (T3SS) found in Gram-negative pathogenic bacteria. The T3SS role is to secrete virulence factors to host cells, leading to diverse diseases. To understand both the bacterial flagellum and its export apparatus, we have been doing structural studies on some flagellar proteins and genetic studies on the export apparatus.
