Identification of residues involved in the interaction of Staphylococcus aureus fibronectin-binding protein with the ⁴F1⁵F1 module pair of human fibronectin using heteronuclear NMR spectroscopy

Many pathogenic Gram-positive bacteria express cell surface proteins that bind to components of the extracellular matrix. This paper describes studies of the interaction between ligand binding repeats (D3 and D1-D4) of a fibronectin-binding protein from Staphylococcus aureus with a module pair (⁴F1⁵F1) from the N-terminal region of fibronectin. When D3 was added to isotope-labeled ⁴F1⁵F1, ¹H, ¹⁵N, and ¹³C NMR chemical shift changes indicate that binding is primarily via residues in ⁴F1, although a few residues in ⁵F1 are also affected. Both hydrophobic and electrostatic interactions appear to be involved. The NMR data indicate that part of the D3 repeat converts from a disordered to a more ordered, extended conformation on binding to ⁴F1⁵F1. In further NMR experiments, selective reduction of the intensity of D1-D4 resonances was observed on binding to ⁴F1⁵F1, consistent with previous suggestions that in each of D1, D2, and D3 repeats, the main fibronectin binding site is in the C-terminal region of the repeat. In D1-D4, these regions also appear to go from a disordered to a more ordered conformation of fibronectin binding. Although the regions of the two proteins which interact had been previously identified, the findings presented here identify, for the first time, the specific residues in both proteins that are likely to be involved in the interaction.