The Collagen-binding Leech Products rLAPP and Calin Prevent both von Willebrand Factor and α₂β₁ (GPIa/IIa)-I-domain Binding to Collagen in a Different Manner

Summary

Calin and rLAPP are two natural inhibitors that are able to inhibit the vWF-binding and platelet adhesion to collagen both under static and flow conditions. In this study we demonstrate that both rLAPP and Calin prevent α₂I-domain binding to human collagen type I with an IC₅₀ of 5 μg/ml. However, although both vWF and α₂I-domain binding to collagen is prevented by rLAPP and Calin, the latter two do not bind to the same collagen site since Calin only partially could compete with rLAPP for binding to collagen. Also vWF and the α₂I-domain were unable to compete completely with each other for the binding to collagen. So the following hypothesis can be made: the binding sites of vWF and of the α₂I-domain on human collagen type I are different but close to each other since rLAPP could inhibit both interactions, and thus should bind to an overlapping epitope. The Calin preparation on the other hand may still contain two active principles, one interfering with vWF-binding, the other with the α₂I-domain-binding to collagen.

^** Present address: Dr. A. Kerekes, Department of Clinical Chemistry, University of Debrecen Medical School, P.O. Box 40, H-4012 Debrecen, Hungary

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