Constraining the subunit order of rod cyclic nucleotide-gated channels reveals a diagonal arrangement of like subunits

Abstract

Retinal rod cyclic nucleotide-gated channels are composed of α and β subunits. We have explored possible subunit arrangements by expressing tandemly linked dimers of both subunits and examining their responses to three different modulating agents. Channels formed from either α-β or β-α heterodimers had functional properties similar to those formed from coexpressed α and β monomers and to native channels. These results point to an α-β-α-β arrangement. To ensure that heterodimers had not flipped around, we coexpressed α-α dimers with an excess of either β monomers or β-β dimers. Our data indicate that heteromultimers do not form efficiently in an α-α-β-β arrangement. Thus, we propose that native rod cyclic nucleotide-gated channels are arranged with like subunits diagonally opposed: α-β-α-β.