X-ray crystal structure of the fibrinolysis inhibitor α₂-antiplasmin

The serpin 2-antiplasmin (SERPINF2) is the principal inhibitor of plasmin and inhibits fibrinolysis. Accordingly, 2-antiplasmin deficiency in humans results in uncontrolled fibrinolysis and a bleeding disorder. 2-antiplasmin is an unusual serpin, in that it contains extensive N- and C-terminal sequences flanking the serpin domain. The N-terminal sequence is crosslinked to fibrin by factor XIIIa, whereas the C-terminal region mediates the initial interaction with plasmin. To understand how this may happen, we have determined the 2.65 ? X-ray crystal structure of an N-terminal truncated murine 2-antiplasmin. The structure reveals that part of the C-terminal sequence is tightly associated with the body of the serpin. This would be anticipated to position the flexible plasmin-binding portion of the C-terminus in close proximity to the serpin Reactive Centre Loop where it may template serpin / protease interactions.