Modulation of the proteolytic activity of matrix metalloproteinase-2 (gelatinase A) on fibrinogen Susanna MONACO*, Magda GIOIA*†, Janet RODRIGUEZ‡, Giovanni Francesco FASCIGLIONE*, Donato DI PIERRO*, Giulio LUPIDI§, Ludwig KRIPPAHL_, Stefano MARINI* and Massimo COLETTA*†1 *Department of Experimental Medicine and Biochemical Sciences, University of Roma Tor Vergata, Via Montpellier 1, I-00133 Roma, Italy, †Interuniversity Consortium on the Metal Chemistry in Biological Systems (CIRCMSB), P.za Umberto I 1, I-70100 Bari, Italy, ‡Laboratorio de Farmacologia, Centro de Quimica Farmaceutica, 200 y 21, Atabey, 21, Atabey, Playa, P.O. Box 16042, La Habana, Cuba, §Department of Molecular, Cellular and Animal Biology, University of Camerino, Via F. Camerini 2, I-62032 Camerino, Italy, and _Departamento de Quimica, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, 2829-516 Monte de Caparica, Portugal The proteolytic processing of bovine fibrinogen by MMP-2 (gelatinase A), which brings about the formation of a product unable to form fibrin clots, has been studied at 37◦C. Catalytic parameters, although showing a somewhat lower catalytic efficiency with respect to thrombin and plasmin, indeed display values indicating a pathophysiological significance of this process. A parallel molecular modelling study predicts preferential binding of MMP-2 to the β-chain of fibrinogen through its haemopexin-like domain, which has been directly demonstrated by the inhibitory effect in the presence of the exogenous haemopexin-like domain. However, the removal of this domain does not impair the interaction between MMP-2 and fibrinogen, but it dramatically alters the proteolytic mechanism, producing different fragmentation intermediates. The investigation at various pH values between 6.0 and 9.3 indicates a proton-linked behaviour,which is relevant for interpreting the influence on the process by environmental conditions occurring at the site of an injury. Furthermore, the action of MMP-2 on peroxynitrite-treated fibrinogen has been investigated, a situation possibly occurring under oxidative stress. The chemical alteration of fibrinogen, which has been shown to abolish its clotting activity, brings about only limited modifications of the catalytic parameters without altering the main enzymatic mechanism. Key words: fibrinogen, fragmentation, gelatinase A, kinetics, molecular modelling, pH-dependence.