Purification and Subunit Structure of a Putative K+-Channel Protein Identified by Its Binding Properties for Dendrotoxin I
The binding protein for the K+-channel toxin dendrotoxin I was purified from a detergent extract of rat brain membranes. The purification procedure utilized chromatography on DEAE-Trisacryl, affinity chromatography on a dendrotoxin-I-Aca 22 column, and wheat germ agglutinin-Affigel 10 with a final 3800- to 4600-fold enrichment and a recovery of 8-16%. The high affinity (Kd, 40-100 pM) and specificity of the binding site are retained throughout the purification procedure. Analysis of the purified material on silver-stained NaDodSO4/polyacrylamide gel revealed three bands of Mr 76,000-80,000, 38,000, and 35,000. Interestingly, the binding site for 125I-labeled mast cell degranulating peptide, another putative K+-channel ligand from bee venom, which induces long-term potentiation in hippocampus, seems to reside on the same protein complex, as both binding sites copurify through the entire purification protocol.