Purification and Characterization of a Variant of Rhodocetin from Calloselasma rhodostoma (Malayan Pit Viper) Venom

Abstract

Rhodocetin is a novel C-type lectin-related protein (CLP) purified from the venom of Calloselasma rhodostoma. Thus far, it is the only reported CLP whose α and β subunits are not linked by an interdisulfide bond. We report here the isolation of a variant of rhodocetin from a different source of venom. This variant of rhodocetin exhibited a different elution profile in reverse-phase HPLC as compared to the rhodocetin reported in our original publication [Wang et al., (1999), Biochemistry 38, 7584–7593]. Specifically, the α subunit of the variant was eluted at a considerably lower percentage of acetonitrile, which suggested a less hydrophobic polypeptide chain as compared to the original rhodocetin. Using a combination of microcharacterization techniques such as peptide mapping, mass spectrometry, and amino acid sequencing, we identified an amino acid substitution, I63K, in the polypeptide chain that could account for the difference in elution behavior of the α subunit. In addition, we also found a conserved E88D substitution in the β chain which was not apparent during reverse-phase HPLC. However, neither of these substitutions resulted in the alteration of the functional properties of the rhodocetin variant.