Integrin-Like Tethering of Motility Complexes at Bacterial Focal Adhesions

Directed surface motility of metazoan cells and protozoan parasites involves substratum engagement by surface-exposed integrin(-like) adhesins, directionally transported by molecular motors via coupling to the internal cytoskeleton. The predatory deltaproteobacterium Myxococcus xanthus uses a helically-trafficked motor at bacterial focal adhesions to power gliding motility. However, the mechanisms of gliding machinery-substratum coupling and force mechanotransduction between innermembrane motors and substratum are unknown. Herein, we use bead force spectroscopy and TIRF microscopy to characterize CglB as the essential substratum-coupling integrin αI-domain-like adhesin. Protease susceptibility reveals that CglB interacts with a globular-protein-accessorized β-barrel OM display platform, which regulates the cell-surface conformational state and accessibility of the adhesin. Surface retention of CglB is further regulated by a cell-surface metalloprotease, a phenomenon also modulated by the OM display platform. These data depict a complex mechanism for bacterial gliding adhesin secretion, cell-surface anchoring, and processing, with conserved themes between prokaryotic and eukaryotic cell motility.