Plasminogen binding properties of macrophage inflammatory protein (MIP)-2 alpha

The chemokine macrophage inflammatory protein (MIP)-2 alpha was identified as a plasminogen binding protein by phage display analysis. MIP-2 alpha and a truncated form lacking 5 lysine residues in the COOH-terminal region (mu t-MIP-2 alpha) were expressed in E. coli and purified to apparent homogenei ty, Purified MIP-2 alpha but not mut-MIP-2 alpha. bound specifically to pla sminogen. with K-A of 3.7 x 10(9) M-1 for the interaction of plasminogen wi th surface-bound MIP-2 alpha. Binding and competition experiments indicated that the interaction involves the region comprising the first 3 kringles o f plasminogen and the COOH-terminal lysine-rich domain of MIP-2 alpha. Acti vation of plasminogen bound to surface-associated MIP-2 alpha by two-chain urokinase-type plasminogen activator (tcu-PA) was about 2.5-fold more effic ient than in solution (catalytic efficiency k(cat)/K-M of 0.1 mu M(-1)s(-1) as compared to 0.04 mu M(-1)s(-1)). In contrast, binding of plasminogen to MIP-2 alpha in solution was very weak. as evidenced by the absence of comp etition of MIP-2 alpha with lysine-Sepharose or with human THP-1 cells for binding of plasminogen. In agreement with this finding, addition of excess MIP-2 alpha did not affect the main functional properties of plasmin(ogen) in solution, as indicated by unaltered activation rates of plasminogen by t cu-PA or tissue-type plasminogen activator (t-PA), t-PA-mediated fibrinolys is, and inhibition rate of plasmin by alpha(2)-antiplasmin. Thus, associati on of MIP-2 alpha with surfaces exposes its COOH-terminal plasminogen-bindi ng site, and may result in enhanced local plasmin generation.