PMID: 9531048Apr 8, 1998Paper

Identification of a functional epitope in plasminogen activator inhibitor-1, not localized in the reactive center loop

Thrombosis and Haemostasis
S Debrock, Paul J Declerck

Abstract

Plasminogen activator inhibitor-1 (PAI-1) is unique among the serpins because of its conformational flexibility. Previously, we have characterized monoclonal antibodies that neutralize PAI-1 activity by switching the active, inhibitory pathway into the non-inhibitory substrate pathway (10). Here, we report the identification of the epitopes for two of these antibodies, i.e. MA-55F4C12 and MA-33H1 and apply this information to explain their functional effects. Using a random PAI-1 epitope library (11), phages displaying specific PAI-1 fragments were isolated after selective screening for binding onto the respective antibodies. Competition experiments with PAI-1 demonstrated that selected phages react with the antigen-binding site of the antibodies. Comparison of the sequences of the different overlapping inserts, encoding the PAI-1 epitope, with the PAI-1 cDNA sequence revealed that both epitopes, even though not identical, are located between amino acids Glu128 and Ala156 in the PAI-1 molecule. Analysis within the three-dimensional structure of PAI-1 showed that these residues completely cover helix F, which is localized close to the major beta-sheet A. This localization provides a rational basis for explaining the mechanism of...Continue Reading

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