Possesses multiple, substituting fibronectin (Fn) binding regions, each capable of conferring adherence to both soluble and immobilized forms of Fn. This confers to S.aureus the ability to invade endothelial cells both in vivo and in vitro, without requiring additional factors, although in a slow and inefficient way through actin rearrangements in host cells. This invasion process is mediated by integrin alpha-5/beta-1. Promotes bacterial attachment to both soluble and immobilized forms of fibrinogen (Fg) by means of a unique binding site localized within the 17 C-terminal residues of the gamma-chain of human Fg. Both plasma proteins (Fn and Fg) function as a bridge between bacterium and host cell. Promotes attachment to immobilized elastin peptides in a dose-dependent and saturable manner. Promotes attachment to both full-length and segments of immobilized human tropoelastin at multiple sites in a dose and pH-dependent manner. Promotes adherence to and aggregation of activated platelets independently of other S.aureus surface molecules. Is a critical mediator implicated in the induction of experimental endocarditis in rats with catheter-induced aortic vegetations, promoting both colonization and persistence of the bacterium into the host. Anchored to the cell wall by sortase A. Expressed predominantly on cells from early exponential phase of growth. Up-regulated by sigma-B factor during early growth stages but not in later stages, although this positive effect on transcription is most probably indirect. Up-regulated by SarA. Down-regulated by Agr. Fg-binding activity is not regulated by the divalent cations Ca(2+), Mn(2+) or Mg(2+). Deletion of the Fg-binding domain of FnbA abrogates the ability to promote cardiac valve infection and persistence in vivo. The mutagenesis studies described in PubMed:17302800 were done with region A alone and not with the entire protein. Mutants lacking C-terminal residues from the ligand binding A region bind to Fg with a reduced affinity or are unable to bind to both Fg and elastin, depending on the extension of the deletion present in this region. Individual constructs of regions spanning amino acids from 194-336 or 337-511 were unable to bind fibrinogen or elastin. Truncated N-terminus.