Cell surface-associated protein implicated in virulence. Promotes bacterial attachment exclusively to the gamma-chain of human fibrinogen. Induces formation of bacterial clumps, which diminish the ability of group IIA phospholipase A2 to cause bacterial phospholipid hydrolysis and killing. Significantly decreases macrophage phagocytosis possibly thanks to the clumps, clumped bacteria being too large to be phagocytosed. Dominant factor responsible for human platelet aggregation, which may be an important mechanism for initiating infective endocarditis. Enhances spleen cell proliferative response in vitro, contributing significantly to the immunostimulatory activity of S.aureus. Found in a ring-like distribution on the surface (PubMed:18800056). Anchored to the cell wall by sortase A (By similarity). Expressed on cells from both exponential and stationary phases. Up-regulated by sigma-B factor during later growth stages. Sigma-B seems to have a transient enhancing effect on bacterial density in the early stages of infection that it lost during later stages of infection. Fg-binding activity is regulated by the divalent cations Ca(2+) and Mn(2+). Belongs to the serine-aspartate repeat-containing protein (SDr) family.