Identification and characterization of a novel cell-envelope subcomplex crucial for A-motility in M. xanthus
Myxococcus xanthus is a rod-shaped, Gram-negative bacterium that has two different motility systems: the A- and the S-motility system. A-motility allows the movement of single cells, while S-motility is cell-cell contact-dependent and is similar to twitching motility in other bacteria. If genes of o...
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|Summary:||Myxococcus xanthus is a rod-shaped, Gram-negative bacterium that has two different motility systems: the A- and the S-motility system. A-motility allows the movement of single cells, while S-motility is cell-cell contact-dependent and is similar to twitching motility in other bacteria. If genes of one of the motility systems are deleted, cells remain motile by the means of the remaining system. The exact mechanism of A-motility is not known, however it has been shown to be powered by the H+ gradient across the cytoplasmic membrane through the AglRQS motor complex. One of the current A-motility models suggests that proteins involved in this system localize to multiple protein complexes referred to as FAs (Focal Adhesions) that are distributed along the cell body and fixed to the substratum in moving cells while a second model suggest a helical motor model. The FAs were suggested to span all subcellular compartments close to the gliding surface. So far, only few proteins essential for A-motility were found to localize to FAs. Notably, proteins localizing to the outer membrane have so far not been identified as components of FAs. In this study, the function of four proteins that were previously identified as essential for A-motility, GltK, GltB, GltA and GltC was investigated. Bioinformatic predictions suggested that these four proteins localize to the periplasm and outer membrane making them interesting to study as potential candidates for anchoring FAs to the substratum. It was demonstrated that GltB, GltA and GltC are dependent on each other for stability. Furthermore, interaction studies and fractionation analysis strongly indicate that these three A-motility proteins form a complex in the periplasm and outer membrane. Colocalization studies with AglZ revealed that GltB and GltA localize to FAs. Moreover, our analyses on protein localization demonstrate that GltK, GltB, GltA and GltC are essential for the assembly of FAs. Vice versa, GltB and GltA incorporation in to FAs depends on other components of FAs including AglZ, AglQ and MglA. Thus, our experiments uncovered the first outer membrane subcomplex essential for the formation of FAs involved in A-motility in M. xanthus.|