Mechanical stabilization of a bacterial adhesion complex.

Abstract

The adhesions between Gram-positive bacteria and their host are exposed to varying magnitudes of tensile forces. Here, using an ultra-stable magnetic-tweezer-based single-molecule approach, we show catch-bond kinetics of the prototypical adhesion complex of SD-repeat protein G to a peptide from fibrinogen β, over a physiologically important force range from piconewton (pN) to tens of pNs which was not technologically accessible to previous studies. The dissociation transition pathway is determined as the unbinding of a critical β-strand peptide (“latch” strand of SdrG that secures the entire adhesion complex) away from its binding cleft, leading to the dissociation of the Fgβ ligand. At 37 oC, the lifetime of the complex exponentially increases from seconds at several pN to ∼1000 s as force reaches 30 pN, leading to mechanical stabilization of the adhesion. Similar mechanical stabilization behavior is also observed in several homologous adhesions, suggesting the generality of catch-bond kinetics in such bacterial adhesions. We reason that such mechanical stabilization allows dynamic bacterial adhesion under low mechanical stress and stable adhesion as force increases, which confers multiple advantages in the pathogenesis and adaptation of bacteria.