THE STRUCTURE OF A SELF-ASSOCIATED COMPLEX OF STROMELYSIN. Garold L. Bryant, Jr., Eric T. Baldwin, Laura C. Kelley & Barry C. Finzel, Structural, Analytical & Medicinal Chemistry, Pharmacia & Upjohn, Inc., Kalamazoo, MI 49007

The matrix metalloproteinase stromelysin (MMP-3) has been the subject of intensive structural studies because of the apparent role of this class of enzymes in chronic inflammation and tumor progression. We report the 1.9 Å structure of an orthorhombic crystal form of the stromelysin catalytic domain (83-255) with two molecules in the asymmetric unit. In this form, the C-terminal residues of one molecule are bound in the P1-P3 subsites of the second molecule, with the carboxylate of Thr²⁵⁵ coordinated to the catalytic zinc. Most previously published peptidic inhibitors of both stromelysin and collagenase have bound toward the P' side of the substrate binding cleft. This self-complex reveals features of peptide binding on the P side. The substrate binding cleft is much wider on this side, and the bound peptide is found to lie along one edge of the cleft, making hydrogen bonds to the outermost strand ([[beta]]IV) of the beta sheet that dominates the MMP folding topology. The S1 (Thr²⁵⁵) and S2 (Glu²⁵⁴) sidechains make no specific interactions with the enzyme, but the sidechain of S3 (Pro²⁵³) is nestled into a strongly hydrophobic P3 specificity pocket formed by a juxtaposition of aromatic protein side chains (Tyr¹⁵⁵, His¹⁶⁶, Tyr¹⁶⁸). In the absence of any inhibitor occupying the P1'-P3' sites, a surrounding portion of the stromelysin structure possesses considerable flexibility.