Vitronectin effects on recombinant plasminogen activator inhibitor-1: structural and functional analysis

Functionally active recombinant plasminogen activator inhibitor-1 (rPAI-1) has been purified from bacterial cells in the absence of any discrete binding protein. In the present study, vitronectin, which is known to stabilise the natural form of PAI-1, was evaluated for its effects on the activity and structure of rPAI-1. As assessed by PAI-1 activity assays, purified human vitronectin was shown to stabilise rPAI-1, by doubling its half-life at 25° and 37°C, and to enhance the activity of rPAI-1 in concentration-dependent fashion. Vitronectin also restored partial activity to a latent form of rPAI-1 prepared by a 72h incubation at 37°C. Fluorescence spectroscopy studies revealed that rPAI-1 in association with vitronectin displayed a higher tryptophan emission signal than the sum of the emissions of the individual components. These results suggest that vitronectin effects on rPAI-1 activity may result from specific conformational effects induced upon binding of the two proteins.