Chiu, Po-LinPagel, Matthew D.Evans, JamesChou, Hui-TingZeng, XiangyanGipson, BryantStahlberg, HenningNimigean, Crina M.2020-02-132020-02-132020-02-132007-09-0110.1016/j.str.2007.06.020https://infoscience.epfl.ch/handle/20.500.14299/165357The gating ring of cyclic nucleotide-modulated channels is proposed to be either a two-fold symmetric dimer of dinners or a four-fold symmetric tetramer based on high-resolution structure data of soluble cyclic nucleotide-binding domains and functional data on intact channels. We addressed this controversy by obtaining structural data on an intact, full-length, cyclic nucleotide-modulated potassium channel, MloK1, from Mesorhizobium loti, which also features a putative voltage-sensor. We present here the 3D single-particle structure by transmission electron microscopy and the projection map of membrane-reconstituted 2D crystals of MloK1 in the presence of cAMP. Our data show a four-fold symmetric arrangement of the CNBDs, separated by discrete gaps. A homology model for full-length MloK1 suggests a vertical orientation for the CNBDs. The 2D crystal packing in the membrane-embedded state is compatible with the S1-S4 domains in the vertical "up" state.text::journal::journal article::research article