EC3, a novel heterodimeric disintegrin from Echis carinatus venom, inhibits α4 and α5 integrins in an RGD-independent manner

EC3, a heterodimeric disintegrin (M-r = 14,762) isolated from Echis carinatus venom is a potent antagonist of alpha 4 integrins, Two subunits called EC3A and EC3B were isolated from reduced and alkylated EC3 by reverse phase high performance liquid chromatography, Each subunit contained 67 residues, including 10 cysteines, and displayed a high degree of homology to each other and to other disintegrins, EC3 inhibited adhesion of cells expressing alpha 4 beta 1 and alpha 4 beta 7 integrins to natural ligands vascular cell adhesion molecule 1 (VCAM-1) and mucosal addressin cell adhesion molecule 1 (MadCAM-1) with IC50 = 630 nM, adhesion of K562 cells (alpha 5 beta 1) to fibronectin with IC50 = 150 nM, and adhesion of alpha IIb beta 3 Chinese hamster ovary cells to fibrinogen with IC50 500 nM; it did not inhibit adhesion of alpha v beta 3 Chinese hamster ovary cells to vitronectin, Ethylpyridylethylated EC3B inhibited adhesion of Jurkat cells to immobilized VCAM-1 (IC50 = 6 mu M), whereas EC3A was inactive in this system. The MLDG motif appeared to be essential for activity of EC3B, Linear MLDG peptide inhibited the adhesion of Jurkat to VCAM-1 in a dose-dependent manner (IC50 = 4 mM), whereas RGDS peptide was not active at the same concentration. MLDG partially inhibited adhesion of K562 cells to fibronectin (5-10 mM) in contrast to RGDS peptide (IC50 = 3 mM), inhibiting completely at 10 mM.