Structure-function relationships of variegin: A novel class of thrombin inhibitors

Abstract

Saliva from hematophagus animals are excellent sources for anti-hemostatic molecules. Thrombin inhibitors present in the salivary gland extract of Amblyomma variegatum were isolated, including variegin, one of the smallest (32 residues) found in nature. It belongs to a novel class of thrombin inhibitors. The structure-function relationships of variegin were examined with synthetic peptides. Three-dimensional structure of variegin-thrombin complex was determined by X-ray crystallography. Based on variegin-thrombin structure as well as the prior knowledge on thrombin inhibitors, a series of peptides were designed to understand thrombin-variegin interactions. These peptides cover a diverse spectrum of potency, kinetics and mechanism of inhibition. In vivo antithrombotic effects of selected peptides were examined by venous thrombosis model of zebrafish larvae. The ability of protamine sulfate to reverse activities of these peptides was also demonstrated. In summary, this work lays the foundation for one of these peptides to be developed into a new anticoagulant.