DIRECT INTERACTION BETWEEN AMINO-TERMINAL AND CARBOXYL-TERMINAL DOMAINS OF CYCLIC NUCLEOTIDE-GATED CHANNELS

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