Complete Amino Acid Sequence of an Acidic, Cardiotoxic Phospholipase A2from the Venom ofOphiophagus hannah(King Cobra): A Novel Cobra Venom Enzyme with “Pancreatic Loop”

A phospholipase A2(OHV A-PLA2) from the venom ofOphiophagus hannah(King cobra) is an acidic protein exhibiting cardiotoxicity, myotoxicity, and antiplatelet activity. The complete amino acid sequence of OHV A-PLA2has been determined using a combination of Edman degradation and mass spectrometric techniques. OHV A-PLA2is composed of a single chain of 124 amino acid residues with 14 cysteines and a calculated molecular weight of 13719 Da. It contains the loop of residues (62–66) found in pancreatic PLA2s and hence belongs to class IB enzymes. This pancreatic loop is between two proline residues (Pro 59 and Pro 68) and contains several hydrophilic amino acids (Ser and Asp). This region has high degree of conformational flexibility and is on the surface of the molecule, and hence it may be a potential protein-protein interaction site. A relatively low sequence homology is found between OHV A-PLA2and other known cardiotoxic PLA2s, and hence a contiguous segment could not be identified as a site responsible for the cardiotoxic activity.