A carboxy-terminal alpha-helical segment in the rat skeletal muscle voltage-dependent Na+ channel is responsible for its interaction with the amino-terminus

Cytoplasmic segments of the: adult rat skeletal muscle sodium channel cc-su bunit (rSkM1) comprise a major portion (similar to 40%) of the total protei n and are involved in channel functions both general, such as inactivation, and isoform-specific, for example, protein kinase A modulation. Far ultrav iolet circular dichroism measurements of synthetic peptides and overexpress ed fusion proteins containing individual channel cytoplasmic segments sugge st that cytoplasmic domains of rSkM1 contain ordered secondary structures e ven in the absence of adjoining transmembrane segments, Intrinsic fluoresce nce experiments with a nested set of carboxy-terminal deletion proteins con firm a specific interaction between the channels amino- and carboxy-termini and identify residues 1716-1737 in the carboxy-terminus as the region that binds to the amino-terminus. Circular dichroism measurements suggest that this same region is organized as an alpha-helix and that electrostatic forc es may contribute to this association. The interaction of the amino- and ca rboxy-termini is not accompanied by secondary structure changes detectable by circular dichroism spectroscopy, but a decrease in intrinsic fluorescenc e indicates that this association is accompanied by a change in the environ ment of Trp(1617). (C) 2000 Elsevier Science B.V. All rights reserved.