Summary
The chemokine macrophage inflammatory protein (MIP)-2α was identified as a plasminogen
binding protein by phage display analysis. MIP-2α and a truncated form lacking 5 lysine
residues in the COOHterminal region (mut-MIP-2α) were expressed in E. coli and purified to apparent homogeneity. Purified MIP-2α but not mut-MIP-2α bound specifically
to plasminogen, with KA of 3.7×105 M−1 for the interaction of plasminogen with surface-bound MIP-2α. Binding and competition
experiments indicated that the interaction involves the region comprising the first
3 kringles of plasminogen and the COOH-terminal lysine-rich domain of MIP-2α. Activation
of plasminogen bound to surface-associated MIP-2α by two-chain urokinase-type plasminogen
activator (tcu-PA) was about 2.5-fold more efficient than in solution (catalytic efficiency
kcat/KM of 0.1 µM−1s−1, as compared to 0.04 µM−1s−1). In contrast, binding of plasminogen to MIP-2α in solution was very weak, as evidenced
by the absence of competition of MIP-2α with lysine-Sepharose or with human THP-1
cells for binding of plasminogen. In agreement with this finding, addition of excess
MIP-2α did not affect the main functional properties of plasmin(ogen) in solution,
as indicated by unaltered activation rates of plasminogen by tcu-PA or tissuetype
plasminogen activator (t-PA), t-PA-mediated fibrinolysis, and inhibition rate of plasmin
by α2-antiplasmin. Thus, association of MIP-2α with surfaces exposes its COOH-terminal
plasminogen-binding site, and may result in enhanced local plasmin generation.
Keywords
MIP-2α - plasminogen - phage display