The Structure of the Prokaryotic Cyclic Nucleotide-Modulated Potassium Channel MloK1 at 16 Å Resolution

• DOI: 10.1016/j.str.2007.06.020
• Publication Date: 2007-09-12T11:21:58Z
• Authors: Po-Lin Chiu; Matthew D. Pagel; James Evans; Hui-Ting Chou; Xiangyan Zeng; Bryant Gipson; Henning Stahlberg; Crina M. Nimigean
• Keywords: Models, Molecular; Crystallography; Potassium Channels; Sequence Homology, Amino Acid; Protein Conformation; Molecular Sequence Data; MOLNEURO; Microscopy, Electron, Transmission; SIGNALING; Structural Biology; Cyclic AMP; CELLBIO; Amino Acid Sequence; Molecular Biology; Rhizobium

The gating ring of cyclic nucleotide-modulated channels is proposed to be either a two-fold symmetric dimer of dimers 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.