Structural Characterization of EMS16, an Antagonist of Collagen Receptor (GPIa/IIa) from the Venom of Echis multisquamatus,

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Abstract
Snake venoms contain a number of hemostatically active C-type lectin-like proteins (CLPs), which affect the blood coagulation system, endothelial cells, and platelets. CLPs have broad similarities in structure and possess distinct biological functions. EMS16, a CLP from Echis multisquamatus venom, which is a potent and selective inhibitor of the collagen receptor, glycoprotein Ia/IIa (integrin α2β1), has been used in the present study to examine structure−function relationships in venom CLPs by X-ray crystallography. The structure of EMS16, determined at a resolution of 1.9 Å, revealed a heterodimer involved with domain swapping of the central loop as observed in the structures of other CLPs. A part of the glycan was observed and identified as N-acetyl-d-glucosamine (GlcNAc) in the electron density map at Asn21 of subunit B, an expected glycosylation site. EMS16 had a unique, positively charged electrostatic potential patch on the concave surface that may qualify as a site for interaction with the I-domain of the glycoprotein Ia/IIa.