Flagellar Motor: Molecular Architecture In Situ
Bacterial flagellae are helical filaments propelled by rotary motors, remarkable nanomachines embedded in the bacterial cell envelope. Powered by a proton or sodium gradient across the cytoplasmic membrane, the flagellar motor converts electrochemical energy into torque by interacting with the stator, a surrounding protein assembly embedded in the cytoplasmic membrane. Of the approximately 50 genes involved in the expression and assembly of the flagellum, about 20 produce protein components of the flagellar motor. The process of flagellar assembly is well understood from extensive studies on assembly-defective mutants in two model systems Salmonella enterica and Escherichia coli. Structural studies have also revealed the molecular architecture of the rotor in great detail. However, the mechanism of flagellar rotation remains poorly understood at the molecular level, mainly because of the lack of structural information about the intact flagellar...