The Flagellum Sample Clauses

The Flagellum. The flagellum is commonly divided into three substructures: the basal body, the hook, and the filament. The structures of the basal body anchor the flagellum to the membrane and comprise the motor that generates flagellar rotation (111). The hook acts as the joint to connect the basal body to the filament (112). Thousands of flagellin protein subunits polymerize to form the filament which extends from the cell body to propel the bacterium forward (105, 113). Flagella are self-assembled in a multi-stage process that begins with the coordinated assembly of the flagellar type III secretion system (T3SS) and some of the basal body structures. The structures of the basal body important for anchoring the flagellum to the cell are a series of rings and a rod. The MS-ring (located on both sides of the cytoplasmic membrane) and the C-ring (located at the cytoplasmic face) form a scaffold for the assembly of the flagellar T3SS cytoplasmic components. The P-ring and the L-ring (present only in Gram-negative bacteria) are incorporated, respectively, into the planes of the peptidoglycan and lipopolysaccharide as the flagellar T3SS assembles (114). The assembled T3SS is now provided with a channel for the export of the basal body rod, followed by the hook proteins, and finally the flagellar filament (115). Late proteins that move through the T3SS to comprise the hook or filament can be contained within secretion chaperones (116-118). Export is driven by an ATPase complex that associates with the cytoplasmic C-ring (119), and is controlled by capping proteins of the hook, rod, and filament. The capping protein of the filament is released by a late secretion chaperone to signal the end of complex assembly (120-122). The motor behind flagellar rotation is driven by proton motive force. The two parts of the motor are the rotor (rotating basal structure) and the stator (stationary ion- conducting complexes). The rotor is made of the C-ring, located at the base of the newly assembled flagellum, the MS-ring, and the rod (123). The C-ring is composed of three proteins known as the “switch complex” (124). The stator is made up of two proteins: XxxX, which interacts with the switch complex, and MotB, a membrane-embedded protein that holds the complex in place and shuffles proteins through the motor (125, 126). Protonation of MotB induces a conformational change in XxxX resulting in a charge-charge interaction between XxxX and the switch complex (127, 128). This induces movement o...