Substrate specificity of the human matrix metalloproteinase stromelysin and the development of continuous fluorometric assays.

To probe the specificity of the metalloendoproteinase stromelysin toward peptide substrates, we determined kc/Km values for the stromelysin-catalyzed hydrolyses of peptides whose design was based loosely on the structure of a known SLN substrate, substance P (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-MetNH2, hydrolysis at Gln-Phe, kc/Km = 1700 M-1 s-1). Several noteworthy points emerge from this study: (i) Catalytic efficiency is dependent on peptide chain length with N-terminal truncation of substance P resulting in more pronounced rate-constant reductions than C-terminal truncation. These results suggest the existence of an extended active site for stromelysin. (ii) Preferences at positions P3, P2, P1, P1', and P2' are for the hydrophobic amino acids Pro, Leu, Ala, Nva, and Trp, respectively. (iii) Investigation of specificity at P3' supports our earlier hypothesis that SLN has a requirement for a hydrogen-bond donor at this position in its substrates. Based on these observations, we designed and had synthesized the fluorogenic substrate N-(2,4-dinitrophenyl)Arg-Pro-Lys-Pro-Leu-Ala-Nva-TrpNH2, whose stromelysin-catalyzed hydrolysis can be monitored continuously (kc/Km = 45,000 M-1 s-1).