Mechanical Forces Guiding Staphylococcus aureus Cellular Invasion

Abstract

Staphylococcus aureus can invade various types of mammalian cells, thereby enabling it to evade host immune defenses and antibiotics. The current model for cellular invasion involves the interaction between the bacterial cell surface located fibronectin (Fn)-binding proteins (FnBPA and FnBPB) and the α5β1 integrin in the host cell membrane. While it is believed that the extracellular matrix protein Fn serves as a bridging molecule between FnBPs and integrins, the fundamental forces involved are not known. Using single-cell and single-molecule experiments, we unravel the molecular forces guiding S. aureus cellular invasion, focusing on the prototypical three-component FnBPA-Fn-integrin interaction. We show that FnBPA mediates bacterial adhesion to soluble Fn via strong forces (∼1500 pN), consistent with a high-affinity tandem β-zipper, and that the FnBPA-Fn complex further binds to immobilized α5β1 integrins with a strength much higher than that of the classical Fn-integrin bond (∼100 pN). The high mechanical stability of the Fn bridge favors an invasion model in which Fn binding by FnBPA leads to the exposure of cryptic integrin-binding sites via allosteric activation, which in turn engage in a strong interaction with integrins. This activation mechanism emphasizes the importance of protein mechanobiology in regulating bacterial-host adhesion. We also find that Fn-dependent adhesion between S. aureus and endothelial cells strengthens with time, suggesting that internalization occurs within a few minutes. Collectively, our results provide a molecular foundation for the ability of FnBPA to trigger host cell invasion by S. aureus and offer promising prospects for the development of therapeutic approaches against intracellular pathogens.

Molecular interaction and inhibition of SARS-CoV-2 binding to the ACE2 receptor

“…8 ). For integrins, injection of cRGD only reduces the binding frequency of ~1–2% on both cell types, which is in good agreement with the fact that integrins are mostly expressed on the bottom of the cell 26 . Altogether, these data obtained on cells by AFM represent to date the best evidence that S1–ACE2 complex is established in physiologically relevant conditions and underlines the complex situation with multiple cell-surface receptors accounting for the whole interaction.…”

What makes bacterial pathogens so sticky?

“…Recently, advanced AFM experiments with controlled surface chemistry enabled to resolve this discrepancy. The force required to separate staphylococcal FnBPA and SpsD adhesins (Prystopiuk et al, ) from Fn was shown to be extremely strong (~1,500–2,000 pN), a unusual mechanostability which originates from the β‐sheet organization of a tandem β‐zipper (Schwarz‐Linek et al, ). Upon binding to FnI modules, the intrinsically disordered binding sequences of the adhesins shift into an ordered structure by forming additional β‐strands along triple peptide β‐sheets in the Fn molecule.…”

“…A striking finding is that S. aureus cellular invasion involves protein bridges between bacterial adhesins and integrins on host cells that are extremely strong. Force spectroscopy experiments showed that FnBPA bind to Fn via a mechanically strong β‐zipper structure (∼1,500 pN), which further binds to α5β1 integrins with a strength much higher than that of the classical Fn−integrin bond (∼100 pN) (Prystopiuk et al, ). This suggests an activation mechanism in which Fn binding by FnBPA leads to the exposure of cryptic integrin‐binding sites via allosteric activation, which in turn engage in a strong interaction with integrins.…”

Heterogeneous Strategies to Eliminate Intracellular Bacterial Pathogens

“…This interaction relies greatly on the extracellular matrix protein Fn that acts as a bridging molecule between FnBPs and integrins. Using singlecell and single-molecule experiments, Prystopiuk et al (2018) showed that FnBPA binds to Fn via a β-zipper-like structure, and this complex in turn enhances bacterial attachment to host cells through forming a strong link with the α5β 1 integrin.…”