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

Abstract

Staphylococcus aureus forms biofilms on indwelling medical devices using a variety of cell-surface proteins. There is growing evidence that specific homophilic interactions between these proteins represent an important mechanism of cell accumulation during biofilm formation, but the underlying molecular mechanisms are still not well-understood. Here we report the direct measurement of homophilic binding forces by the serine-aspartate repeat protein SdrC and their inhibition by a peptide. Using single-cell and single-molecule force measurements, we find that SdrC is engaged in low-affinity homophilic bonds that promote cell-cell adhesion. Low-affinity intercellular adhesion may play a role in favoring biofilm dynamics. We show that SdrC also mediates strong cellular interactions with hydrophobic surfaces, which are likely to be involved in the initial attachment to biomaterials, the first stage of biofilm formation. Furthermore, we demonstrate that a peptide derived from β-neurexin is a powerful competitive inhibitor capable of efficiently blocking surface attachment, homophilic adhesion, and biofilm accumulation. Molecular modeling suggests that this blocking activity may originate from binding of the peptide to a sequence of SdrC involved in homophilic interactions. Our study opens up avenues for understanding the role of homophilic interactions in staphylococcal adhesion, and for the design of new molecules to prevent biofilm formation during infection.Staphylococcus aureus | SdrC | adhesion | biofilms | inhibition T he nosocomial pathogen Staphylococcus aureus is a major cause of superficial and invasive infections. A remarkable trait of this bacterium is its ability to form biofilms on implanted devices, thereby triggering infections that are difficult to treat with antibiotics (1, 2). Biofilm formation is initiated by attachment of the bacteria to abiotic surfaces, protein-coated materials, and host cells, and followed by cell-cell adhesion and multiplication leading to a mature biofilm (1, 2). A variety of cell-surface components are involved in intercellular interactions (2, 3). Although the polycationic polysaccharide intercellular adhesin has long been thought to be the main component promoting intercellular adhesion (4, 5), there is now a compelling body of evidence that cell wall-anchored (CWA) proteins are also involved (2, 3). Several recombinant CWA proteins have been shown to form dimers in solution (6-9). In some cases (i.e., Aap), crystallographic studies have provided insights into the mechanism of dimer formation (9, 10). Although very useful, in vitro methods provide information on purified molecules that are removed from their cellular context. Clearly, elucidating the molecular mechanisms by which CWA proteins self-associate in vivo is key to enhancing our understanding of biofilm accumulation.The increase of multidrug-resistant strains has created an urgent need for new therapeutics for bacterial infections. Biofilm inhibitors, where bacteria are prevented from forming biofilms rather than...

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