Prostromelysin-1 (proMMP-3) stimulates plasminogen activation by tissue-type plasminogen activator

Matrix metalloproteinase-3 (MMP-3 or stromelysin-1) specifically binds to t issue-type plasminogen activator (t-PA), without however, hydrolyzing the p rotein. Binding affinity to proMMP-3 is similar to single chain t-PA, two c hain t-PA and active site mutagenized t-PA (K-a of 6.3 x 10(6) to 8.0 x 10( 6) m(-1)), but is reduced for t-PA lacking the finger and growth factor dom ains (K-a of 2.0 x 10(6) m(-1)). Activation of native Glu-plasminogen by t- PA in the presence of proMMP-3 obeys Michaelis-Menten kinetics; at saturati ng concentrations of proMMP-3, the catalytic efficiency of two chain t-PA i s enhanced 20-fold (k(cat)/K-m of 7.9 x 10(-3) vs. 4.1 x 10(-4) mu m(-1).s( -1)). This is mainly the result of an enhanced affinity of t-PA for its sub strate (K-m of 1.6 mu m vs. 89 mu m in the absence of proMMP-3), whereas th e k(cat) is less affected (k(cat) of 1.3 x 10(-2) vs. 3.6 x 10(-2) s(-1)). Activation of Lys-plasminogen by two chain t-PA is stimulated about 13-fold at a saturating concentration of proMMP-3, whereas that of miniplasminogen is virtually unaffected (1.4-fold). Plasminogen activation by single chain t-PA is stimulated about ninefold by proMMP-3, whereas that by the mutant lacking finger and growth factor domains is stimulated only threefold. Bios pecific interaction analysis revealed binding of Lys-plasminogen to proMMP- 3 with 18-fold higher affinity (K-a of 22 x 10(6) m(-1)) and of miniplasmin ogen with fivefold lower affinity (K-a of 0.26 x 10(6) m(-1)) as compared t o Glu-plasminogen (K-a of 1.2 x 10(6) m(-1)). Plasminogen and t-PA appear t o bind to different sites on proMMP-3. These data are compatible with a mod el in which both plasminogen and t-PA bind to proMMP-3, resulting in a cycl ic ternary complex in which t-PA has an enhanced affinity for plasminogen, which may be in a Lys-plasminogen-like conformation. Maximal binding and st imulation require the N-terminal finger and growth factor domains of t-PA a nd the N-terminal kringle domains of plasminogen.