Direct interaction between amino- and carboxyl-terminal domains of cyclic nucleotide-gated channels

We have examined domain interactions in the rod cyclic nucleotide-gated ion channel using both physiological and biochemical interaction assays. We have found an interaction between two regions of the channel distant in primary structure, the amino-terminal region and the carboxyl-terminal region containing the cyclic nucleotide-binding (CNB) domain. The interaction in functional channels was detected by the formation of a disulfide bond between cysteine residues at position 35 in the amino-terminal region and 481 in the carboxyl-terminal region. The disulfide bond resulted in channel potentiation, which was due, in part, to an increase in availability of C481 to modification when the channels were open. This state dependence is likely to underlie previously reported potentiation of cyclic nucleotide-gated channels by sulfhydryl-reactive compounds. Polypeptides derived from the aminoterminal and carboxyl-terminal regions were shown to interact, even under conditions which precluded disulfide bond formation. These data argue for a previously unknown, direct interaction between disparate regions of channel sequence.