Dual-Site Recognition of Different Extracellular Matrix Components by Anti-Angiogenic/Neurotrophic Serpin, PEDF

Pigment epithelium-derived factor (PEDF), a member of the serine protease inhibitor (serpin)
superfamily, possesses anti-angiogenic and neurotrophic activities. PEDF has been reported to bind to
extracellular matrix (ECM) components such as collagens and glycosaminoglycans (GAGs). In this study,
to determine the binding sites for collagens and GAGs, we analyzed the interaction of recombinant mouse
PEDF (rPEDF) with collagen I and heparin. By utilizing residue-specific chemical modification and site-directed mutagenesis techniques, we revealed that the acidic amino acid residues on PEDF (Asp255, Asp257,
and Asp299) are critical to collagen binding, and three clustered basic amino acid residues (Arg145, Lys146,
and Arg148) are necessary for heparin binding. Mapping of these residues on the crystal structure of human
PEDF (Simonovic, M., Gettins, P. G. W., and Volz, K. (2001) Proc. Natl. Acad. Sci. U.S.A. 98, 11131−11135) demonstrated that the collagen-binding site is oriented toward the opposite side of the highly
basic surface where the heparin-binding site is localized. These results indicate that PEDF possesses dual
binding sites for different ECM components, and this unique localization of ECM-binding sites implies
that the binding to ECM components could regulate PEDF activities.