CRITICAL ROLE OF GLUTAMATE IN A CENTRAL LEUCINE-RICH REPEAT OF DECORIN FOR INTERACTION WITH TYPE-I COLLAGEN

The chondroitin/dermatan sulfate proteoglycan decorin is known to inte ract via its core protein with fibrillar collagens, thereby influencin g the kinetics of fibril formation and the final diameter of the fibri ls. To define the binding site(s) for type I collagen along the core p rotein, which is mainly composed of leucine-rich repeat structures, de corin cDNAs were constructed and expressed in human kidney 293 cells. The constructs encoded (i) C-terminally truncated molecules, (ii) core proteins with deletions of selected leucine-rich repeats, or (iii) va rious point mutations, The deletion of the sixth leucine-rich repeat M et(176)-Lys(201) and the mutation E180K drastically interfered with th e binding to reconstituted type I collagen fibrils, In contrast, the d eletion of the seventh repeat Leu(202)-Ser(222) led at the most to a m arginally impaired binding, although the secretion of this proteoglyca n was abnormally low. Decorin with two other point mutations in the si xth leucine-rich repeat, Lys(187) --> Gln and Lys(200) --> Gln, respec tively, bound type I collagen either normally or even better than the normal recombinant proteoylycan. These data suggest that a major colla gen-binding site of decorin is located within the sixth leucine-rich r epeat and that glutamate-180 within this repeat is of special importan ce for ionic interactions between the two matrix components.