variabilin and arginyl-glycyl-aspartic-acid

A novel inhibitor of human platelet aggregation, named variabilin, was isolated from salivary glands of the hard tick Dermacentor variabilis using a combination of gel filtration and high pressure liquid chromatography. Variabilin was a potent antagonist of the fibrinogen receptor glycoprotein IIb-IIIa (GPIIb-IIIa; alphaIIbbeta3) and the vitronectin receptor alphavbeta3. Amino acid sequence analysis by Edman degradation revealed that it has 47 residues, with a molecular weight of 4968.5. Like many other naturally occurring antagonists of GPIIb-IIIa, variabilin contains the RGD (Arg-Gly-Asp) motif. However, unlike the RGD-containing antagonists of GPIIb-IIIa, the RGD sequence of variabilin is not positioned in a loop bracketed by cysteine residues. It has little sequence homology to the other known naturally occurring antagonists of GPIIb-IIIa, including the disintegrins from snakes, decorsin and ornatin from leeches, and disagregin from soft ticks. Variabilin is the first RGD-containing antagonist isolated from ticks.

Topics: Amino Acid Sequence; Animals; Cell Adhesion; Chromatography, High Pressure Liquid; Dermacentor; Dose-Response Relationship, Drug; Humans; Mass Spectrometry; Molecular Sequence Data; Molecular Weight; Oligopeptides; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIIb-IIIa Complex; Proteins; Salivary Glands; Sequence Analysis