FnBPs

FnBPs, short for fibronectin-binding proteins, are a class of surface-anchored adhesins found in several Gram-positive bacteria, most notably Staphylococcus aureus, where two major proteins, FnBPA and FnBPB, contribute to adherence and invasion. They bind fibronectin, a host extracellular matrix glycoprotein, enabling the bacteria to attach to and invade host tissues.

Structure and localization: FnBPs are cell wall-anchored proteins that possess an LPXTG sorting motif, allowing covalent attachment to the peptidoglycan layer via sortase A. The extracellular region contains repetitive fibronectin-binding domains that recognize fibronectin's modules.

Function: Binding to fibronectin forms a bridge to host cell integrins, particularly α5β1, promoting internalization of bacteria by non-professional phagocytes and colonization of tissues. FnBPs also facilitate adherence to various surfaces and can contribute to biofilm formation under certain conditions.

Role in disease and regulation: In Staphylococcus aureus infections, FnBPs participate in colonization and dissemination, contributing to endovascular and soft-tissue infections and implant-associated infections. Expression is regulated by global regulatory networks and environmental cues, with higher surface display during infection.

Clinical significance: FnBPs are considered virulence factors and have been explored as components of vaccines or therapeutic targets aiming to block initial adherence and invasion.