Thrombospondin-1 (TSP-1) is a 150 - 180 kDa charter member of the thrombospondin family of extracellular matrix proteins.1 - 4 Human TSP-1 is synthesized as an 1170 amino acid (aa) precursor that contains an 18 aa signal sequence and 1152 aa mature molecule. The mature molecule has been described as containing three distinct regions that create the shape of a dumbbell. There is an intital, 140 aa N-terminal laminin G-like globular region that binds heparin (aa 19 - 258). This is followed by an extended, central collagen-binding region that contains one type C von Willebrand factor domain, plus three TSP type I and three TSP type II (or EGF-like) domains (aa 259 - 712). The type I repeats have multiple functions. They bind to type IV collagen, laminin, fibronectin and CD36.