Here we report the crystal structure of a stablilized plasminogen activator
inhibitor-1 variant (PAI-1-N150H-K154T-Q301P-Q319L-M354I (PAI-1-stab)) that
shows a cleavage within the reactive centre loop. The new structure is of
superior quality compared to the previously determined structure of the cleaved
PAI-1-A335P mutant. We present a detailed comparison of the two structures and
also compare them with the structure of the active PAI-1-stab. The structural
data give important insights into the working mechanism of PAI-1 and also
explain the role of various stabilizing mutations.