Binding of correolide to K(v)1 family potassium channels - Mapping the domains of high affinity interaction

Correolide, a novel nortriterpene natural product, potently inhibits the vo ltage-gated potassium channel, K(v)1.3, and [H-3]dihydrocorreolide (diTC) b inds with high affinity (K-d similar to 10 nM) to membranes from Chinese ha mster ovary cells that express K(v)1.3 (Felix, J. P., Bugianesi, R. M., Sch malhofer, W. k, Borris, R., Goetz, M. k, Hensens, O. D., Bao, J.-M., Kayser , F., Parsons, W. H., Rupprecht, K., Garcia, M. L., Kaczorowski, G. J., and Slaughter, R. S. (1999) Biochemistry 38, 4922-4930). Mutagenesis studies w ere used to localize the diTC binding site and to design a high affinity re ceptor in the diTC-insensitive channel, K(v)3.2. Transferring the pore from K(v)1.3 to Kv3.2 produces a chimera that binds peptidyl inhibitors of Kv(1 .3) with high affinity, but not diTC. Transfer of the S-6 region of K(v)1.3 to K(v)3.2 reconstitutes diTC binding at 4-fold lower affinity as compared with K(v)1.3, whereas transfer of the entire S-5-S-6 domain results in a n ormal K(v)1.3 phenotype, Substitutions in S-5-S-6 of K(v)1.3 with nonconser ved residues from K(v)3.2 has identified two positions in S-5 and one in S- 6 that cause significant alterations in diTC binding. High affinity diTC bi nding can be conferred to K(v)3.2 after substitution of these three residue s with the corresponding amino acids found in K(v)1.3. These results sugges t that lack of sensitivity of K(v)3.2 to diTC is a consequence of the prese nce of Phe(382) and Ile(387) in S-5 and Met(458) in S-6. Inspection of K(v) 1.1-1.6 channels indicates that they all possess identical S-5 and S-6 doma ins. As expected, diTC binds with high affinity (K, values 7-21 nM) to each of these homotetrameric channels. However, the kinetics of binding are fas test with K(v)1.3 and K(v)1.4, suggesting that conformations associated wit h C-type inactivation will facilitate entry and exit of diTC at its binding site. Taken together, these findings identify K(v)1 channel regions necess ary for high affinity diTC binding, as well as, reveal a channel conformati on that markedly influences the rate of binding of this Ligand.