Elucidation of the epitope of a latency-inducing antibody: identification of a new molecular target for PAI-1 inhibition

Summary

The monoclonal antibody MA-33B8, directed against the serpin plasminogen activator inhibitor-1 (PAI-1), has unique functional properties as it induces acceleration of the active-to-latent transition (Verhamme I et al. J Biol Chem 274: 17511-7, 1999), resulting in PAI-1 activity neutralization. In this study, we have identified Lys⁸⁸, Asp⁸⁹, Lys¹⁷⁶ and His²²⁹ as the major residues of the conformational epitope. Lysine⁸⁸ and aspartic acid⁸⁹, contributing the most, are located on the loop between α-helix D and β-strand 2A. Strikingly, these residues undergo dramatic conformational changes during latency conversion. The three-dimensional localization of this epitope and its differential exposure in active and latent forms of PAI-1 provide a molecular explanation for the underlying mechanism of MA-33B8. Rearrangements of hydrogen bonds in this region upon latency transition, strongly suggest that binding of MA-33B8 may result in the generation of energy required in the rate-limiting step of latency transition. Thus, this novel epitope reveals a new interaction site in PAI-1 as a putative molecular target to modulate PAI-1 activity.

Keywords

PAI-1 - fibrinolysis - epitope mapping - monoclonal antibody

• References

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