Immobilization of the distal hinge in the labile serpin plasminogen activator inhibitor 1: identification of a transition state with distinct conformational and functional properties.

The serpin plasminogen activator inhibitor-1 (PAI-1) plays an important role in the regulation of the fibrinolytic activity in blood. In plasma, PAI-1 circulates mainly in the active conformation. However, PAI-1 spontaneously converts to a latent conformation.