Content area
Full Text
Various rod-shaped bacteria mysteriously glide on surfaces in the absence of appendages such as flagella or pili. In the deltaproteobacterium Myxococcus xanthus, a putative gliding motility machinery (the Agl-Glt complex) localizes to so-called focal adhesion sites (FASs) that form stationary contact points with the underlying surface. Here we show that the Agl-Glt machinery contains an inner-membrane motor complex that moves intracellularly along a right-handed helical path; when the machinery becomes stationary at FASs, the motor complex powers a left-handed rotation of the cell around its long axis. At FASs, force transmission requires cyclic interactions between the molecular motor and the adhesion proteins of the outer membrane via a periplasmic interaction platform, which presumably involves contractile activity of motor components and possible interactions with peptidoglycan. Our results provide a molecular model of bacterial gliding motility.
Certain rod-shape bacteria move along their long axes in the absence of extracellular appendages such as flagella or pili, in a process called gliding motility1. In Myxococcus xanthus, gliding is mediated by bacterial FASs. During gliding motility, FASs assemble at the leading cell pole and retain a fixed position relative to the surface until they disassemble at the lagging cell pole1. FASs contain a molecular machinery, the Agl-Glt (adventurous gliding and gliding transducer) complex. which comprises more than fourteen proteins2-4. Genetic analysis has suggested that this machinery is formed by two membrane-associated systems: (i) a putative three-protein TolQR-like proton motive force (PMF)-driven channel comprising AglR, AglQ and AglS (the suspected energy-producing system)3,5,6; and (ii) a putative eleven-protein integral envelope-associated complex (containing GltA-K) that interacts with the Agl system2-4. These machineries are further connected to a cytosolic protein complex formed by the AglZ protein, the Ras-like G-protein MglA and the MreB actin cytoskeleton (hereafter called the MreB complex7; Fig. 1a). This MreB complex recruits, and promotes the assembly of the Agl-Glt complex (Fig. 1a). Directional movements of the Agl-Glt complex from the leading towards the lagging cell pole have been suggested to propel the cell forward3,8, but how these movements may be transduced into cell movement remains unknown5,9. Here, we reveal the functional architecture of the Agl-Glt complex and establish how its activity is transduced to the contact surface across the highly structured layers of the cell envelope.
Intracellular helically moving...