Identification of a conformationally distinct form of plasminogen activator inhibitor-1, acting as a noninhibitory substrate for tissue-type plasminogen activator.
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.
Declerck
P J
PJ
Center for Thrombosis and Vascular Research, University of Leuven, Belgium.
De Mol
M
M
Vaughan
D E
DE
Collen
D
D
D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006868:Hydrolysis; D015849:Plasminogen Inactivators / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity; D010959:Tissue Plasminogen Activator / Q000378:metabolism*
D015849:Plasminogen Inactivators; D011994:Recombinant Proteins; D010959:Tissue Plasminogen Activator