A MODEL OF THE REACTIVE FORM OF PLASMINOGEN-ACTIVATOR INHIBITOR-1

A model of the reactive form of plasminogen activator inhibitor-1 (PAI -1) has been constructed using molecular graphics and starting from th e known crystal structure of latent PAI-1. The residues P16 to P10', o f which P16-P4 form strand 4 of the beta-sheet A (s4A) and P3-P10' for m an extended loop in the latent form, have been removed and remodeled into this structure, based on the structures of ovalbumin and cleaved alpha(1)-proteinase inhibitor. Residues P4'-P10' were remodeled as a beta-strand s1C, located on the surface of the molecule and the N-term inal end (P16-P14) of the eliminated loop was rebuilt using appropriat e backbone dihedrals. Subsequently, a secondary structure prediction p rogram was applied and further optimization of the model was performed by several molecular dynamics runs. Apparently the beta-strand was st abilized by only two hydrogen bonds. Further analysis revealed that, a lthough s4A was removed, s3A and s5A did not approach each other. In t his current model it was also found that the large gap between the loo p connecting s4C-s3C and the loop connecting s3B-hG remained 11 Angstr om in contrast to the small gap (4 Angstrom) at a similar position in other serpins. These observations may explain the ease of a conformati onal change of the reactive site loop of PAI-1 during transition to th e latent and the preinserted form. In addition the current model can b e used for the design of stable, functional, PAI-1 mutants. Detailed s tructural analysis of the latter may facilitate studies on the structu re-function relationship in PAI-1 in particular and in other serpins i n general. (C) 1994 Academic Press, Inc.