CHARACTERIZATION OF THE INTERACTIONS OF TYPE-XII COLLAGEN WITH 2 SMALL PROTEOGLYCANS FROM FETAL BOVINE TENDON, DECORIN AND FIBROMODULIN

In addition to the major collagens, such as type I or type II, connect ive tissues contain a number of less abundant collagens and proteoglyc ans, whose association contributes to the different properties of the tissues. Type XII and type XIV collagens have been described in soft c onnective tissues, and type XIV collagen has been shown to interact sp ecifically with decorin through its glycosaminoglycan chain (Font et a l., J. Biol. Chem. 268, 25025-25018, 1993). Interactions between these collagens and the small proteoglycans have been characterized further by studying the binding of type XII: collagen to decorin by solid pha se assays. Our results show a saturable binding of the proteoglycan th rough its glycosaminoglycan chain to type XII collagen, which does not seem to involve the large non-collagenous NC3 domain of the molecule. This interaction is strongly inhibited by heparin. Furthermore, we re port that another small proteoglycan, fibromodulin, isolated from tend on under non-denaturing conditions, is able to bind to type XII collag en. This interaction has been characterized and, unlike that observed with decorin, type XII collagen-fibromodulin interaction seems to take place with the core protein of the proteoglycan. In addition, we repo rt that type XII-type I collagen interactions are not necessarily medi ated by decorin as previously suggested.