& kappa;O-SrVIA Conopeptide, a Novel Inhibitor Peptide for Two Members of the Human EAG Potassium Channel Family

The first conotoxin affecting the voltage-gated potassium channels of the EAG family was identified and characterized from the venom of the vermivorous species Conus spurius from the Gulf of Mexico. This conopeptide, initially named Cs68 and later designated & kappa;O-SrVIA, is extremely hydrophobic and comprises 31 amino acid residues, including six Cysteines in the framework VI/VII, and a free C-terminus. It inhibits the currents mediated by two human EAG subtypes, Kv10.1 (IC50 = 1.88 & PLUSMN; 1.08 & mu;M) and Kv11.1 (IC50 = 2.44 & PLUSMN; 1.06 & mu;M), and also the human subtype Kv1.6 (IC50 = 3.6 & PLUSMN; 1.04 & mu;M). Despite its clear effects on potassium channels, it shares a high sequence identity with & delta;-like-AtVIA and & delta;-TsVIA. Also, & kappa;O-SrVIA is the third conopeptide from the venom of C. spurius with effects on potassium channels, and the seventh conotoxin that blocks Kv1.6 channels.