(Taken from the application): Loss of cartilage through proteolytic degradation of its extracellular matrix (ECM)is an important factor in arthritis. Development of new therapy requires that the mechanisms of ECM catabolism be understood and that molecules having the potential to inhibit the catabolic enzymes be identified. Cleavage of aggrecan at a specific aggrecanase cleavage site leads to leakage of functional aggrecan from cartilage and loss of its unique functional properties. Recent work has identified at least two aggrecanases, which are members of the ADAM-TS family of metalloproteinases. A consistent paradigm in the regulation of catabolic enzymes is the existence of endogenous inhibitors. Specific, locally acting, endogenous inhibitors of aggrecanases or other ADAM-TS have not yet been identified. The underlying hypothesis of this proposal is that such aggrecanase inhibitors which bind to the active site may exist. To address the hypothesis, the specific aim is to use a yeast genetic screen, the two-hybrid system, to identify proteins which interact with the catalytic domain of ADAM-TS4 (aggrecanase 1) and ADAM-TS5 (aggrecanase 2). With this approach we expect, to identify molecules which are substrates, inhibitors, or other interactors in the catalytic activity of aggrecanase. Each of the interacting proteins thus identified offers pathways for designing of inhibitors. For example, endogenous inhibitors can be upregulated or introduced into arthritic joints by gene therapy. Substrates can be modeled to design specific analog inhibitors as has been done in designing hydroxamic acid based MMP inhibitors.