A spectroscopic study of the conformations of active and latent forms of recombinant plasminogen activator inhibitor-1

Recombinant plasminogen activator inhibitor-1 (rPAI-1) purified from Escherichia coli, like its natural counterpart, can exist in either active or latent form. To elucidate the structural basis for these two forms, both active and latent rPAI-1 have been studied using ultra-violet (UV), circular dichroism (CD), and fluorescence spectroscopy. The secondary structures determined by CD show no significant differences and indicate that both the forms are predominantly alpha helical and random. The UV spectra are also very similar with absorption maxima around 278 nm. The structures of the two forms were further characterized by measuring tryptophan fluorescence emissions and their quenching with ionic (iodide) and neutral (acrylamide) quenchers. These data indicate clear differences in the tertiary structures of the two forms with the latent form being more compact and folded in comparison with the active form.