Zinc-dependent mechanical properties of Staphylococcus aureus biofilm-forming surface protein SasG

Abstract

Staphylococcus aureus surface protein SasG promotes cell–cell adhesion during the accumulation phase of biofilm formation, but the molecular basis of this interaction remains poorly understood. Here, we unravel the mechanical properties of SasG on the surface of living bacteria, that is, in its native cellular environment. Nanoscale multiparametric imaging of living bacteria reveals that Zn2+ strongly increases cell wall rigidity and activates the adhesive function of SasG. Single-cell force measurements show that SasG mediates cell–cell adhesion via specific Zn2+-dependent homophilic bonds between β-sheet–rich G5–E domains on neighboring cells. The force required to unfold individual domains is remarkably strong, up to ∼500 pN, thus explaining how SasG can withstand physiological shear forces. We also observe that SasG forms homophilic bonds with the structurally related accumulation-associated protein of Staphylococcus epidermidis, suggesting the possibility of multispecies biofilms during host colonization and infection. Collectively, our findings support a model in which zinc plays a dual role in activating cell–cell adhesion: adsorption of zinc ions to the bacterial cell surface increases cell wall cohesion and favors the projection of elongated SasG proteins away from the cell surface, thereby enabling zinc-dependent homophilic bonds between opposing cells. This work demonstrates an unexpected relationship between mechanics and adhesion in a staphylococcal surface protein, which may represent a general mechanism among bacterial pathogens for activating cell association.

Amyloid Structures as Biofilm Matrix Scaffolds

“…Region C consists of a series of identical repeats of 86 amino acids and is followed by a C-terminal region D containing a serine-aspartate-rich repeated sequence. Because Bap is covalently linked to the cell wall, it was believed that Bap mediated intercellular adhesion through homophilic interactions between opposing proteins in neighboring cells, as has been shown for the SasG protein (60)(61)(62)(63)(64)(65). However, recent results indicate that Bap behaves in a completely different manner.…”

Clumping Factor B Promotes Adherence of Staphylococcus aureus to Corneocytes in Atopic Dermatitis

“…Multiparametric imaging was then used to localize the ligands recognized by S. aureus on the surface of corneocytes from patients 1434 and 1473 (24,25). Multiparametric imaging is a newly developed AFM technique that enables researchers to simultaneously map the structure, biophysical properties, and molecular interactions of biological samples (19).…”

Molecular interactions and inhibition of the staphylococcal biofilm-forming protein SdrC

“…Among these new tools, atomic force microscopy (AFM) allows us to analyze the organization, biophysical properties, and interactions of cell-wall molecules directly in single cells (14,15). During the past years, there has been much progress in applying AFM techniques to explore the forces involved in cell adhesion and biofilm formation by staphylococci, down to molecular resolution (16)(17)(18)(19)(20)(21)(22)(23). Here, we used AFM to study the forces guiding the self-association of the S. aureus serine-aspartate repeat protein SdrC (Fig.…”