The mechanism of R2ab-mediated attachment to polystyrene surfaces in Staphylococcus epidermidis.

The staphylococcal autolysin protein hydrolyzes cell wall peptidoglycans. The R2ab repeats of autolysin guide the catalytic domain by binding to cell wall components and mediate attachment to abiotic surfaces during biofilm formation on polystyrene. Characterizing protein interactions with surfaces is a significant challenge in understanding bacterial attachment. Here, using nuclear magnetic resonance spectroscopy, we determined the solution structure and backbone dynamics of the R2ab domain. We then, by combining nuclear magnetic resonance and calorimetry, identified the interaction mode of R2ab with cell wall components and polystyrene surfaces. The solution-derived R2ab structure reveals interaction surfaces with lipoteichoic acid and peptidoglycan. The binding regions are identified, and docking is used to model their binding to R2ab. R2ab also interacts with polystyrene nanoparticles. Using a novel approach where polystyrene nanoparticles are paramagnetically labeled, we identify the major R2ab-polystyrene interaction interface. R2ab engages polystyrene surfaces via a defined C-terminal interface on R2b, as revealed by PRE mapping, isothermal titration calorimetry, and mutational analyses. Polar and charged residues (notably S776 and K779) play key roles in adsorption. These findings support a model in which R2ab acts as a molecular bridge, binding both cell wall components and abiotic surfaces. This highlights its role in early biofilm formation and suggests that disrupting this interaction could reduce Staphylococcus epidermidis attachment to abiotic surfaces.