The human ENO1 gene product (recombinant human α-enolase) displays characteristics required for a plasminogen binding protein

Plasminogen binds with low affinity in a lysine-dependent manner to many cell types. Previously, a 54 kDa plasminogen receptor found on the surface of U-937 cells was identified as an α-enolase-like molecule. The aims of this study were to determine whether recombinant α-enolase (r-α-enolase), encoded by ENO1, was a plasminogen binding protein and to generate polyclonal antibodies against this antigen. Plasminogen specifically bound r-α-enolase with a K(d) 1.9 μM and approached saturation at 10 μM. Lysine-dependent plasminogen binding to r-α-enolase was demonstrated by a greater than 80% inhibition of binding by the lysine analogues ε-amino caproic acid and tranexamic acid, whilst only 14% inhibition occurred with the arginine analogue benzamidine. Removal of the C-terminal lysine residue of r-α-enolase with carboxypeptidase B significantly reduced its plasminogen binding capacity, suggesting that binding required C-terminal lysine residue of r-α-enolase. Binding to r-α-enolase enhanced the activation rate of plasminogen by urokinase but prevented α2-antiplasmin from binding plasminogen. Taken together, these data suggest that the gene product of human ENO1 encodes an authentic plasminogen binding protein.