Identification of a conformationally distinct form of plasminogen activator inhibitor-1, acting as a noninhibitory substrate for tissue-type plasminogen activator

• Published in: The Journal of biological chemistry 1992-06, Vol.267 (17), p.11693-11696
• Main Authors: Declerck, P J, De Mol, M, Vaughan, D E, Collen, D
• Format: Article
• Language: English
• Subjects: Electrophoresis, Polyacrylamide Gel; Humans; Hydrolysis; Plasminogen Inactivators - chemistry; Plasminogen Inactivators - isolation & purification; Plasminogen Inactivators - metabolism; Protein Conformation; Recombinant Proteins - metabolism; Spectrometry, Fluorescence; Substrate Specificity; Tissue Plasminogen Activator - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(19)49751-2

Plasminogen activator inhibitor-1 (PAI-1), the primary physiological inhibitor of tissue-type plasminogen activator (t-PA) in plasma, is a serine proteinase inhibitor (serpin) that forms a 1:1 stoichiometric complex with its target proteinase leading to the formation of a stable inactive complex. The active, inhibitory form of PAI-1 spontaneously converts to a latent form that can be reactivated by protein denaturants. In the present study we have isolated another molecular form of intact PAI-1 that, in contrast with active PAI-1, does not form stable complexes with t-PA but is cleaved at the P1-P1' bond (Arg346-Met347). Other serine proteinases, e.g. urokinase-type plasminogen activator and thrombin, also cleaved this "substrate" form of PAI-1. Fluorescence spectroscopy revealed conformational differences between the latent, active, and substrate forms of PAI-1. This observation confirms our hypothesis that the three functionally different forms of PAI-1 are the consequence of conformational transitions. Thus PAI-1 may occur in three interconvertible conformations: latent, inhibitor, and substrate PAI-1. The identification of two distinct conformations of PAI-1 which interact with their target protease either as an inhibitor or as a substrate is a previously unrecognized phenomenon among the serpins. Conversion of substrate PAI-1 to its inactive degradation product may constitute a pathway for the physiological regulation of PAI-1 activity.