title: The structure of the prokaryotic cyclic nucleotide-modulated potassium channel MloK1 at 16 A resolution.
abstract: 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.
authors.affiliation: Molecular and Cellular Biology, College of Biological Sciences, University of California-Davis, 1 Shields Avenue, Davis, CA 95616, USA.
authors.forename: Po-Lin
authors.initials: PL
authors.lastname: Chiu
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Pagel
authors.forename: James
authors.initials: J
authors.lastname: Evans
authors.forename: Hui-Ting
authors.initials: HT
authors.lastname: Chou
authors.forename: Xiangyan
authors.initials: X
authors.lastname: Zeng
authors.forename: Bryant
authors.initials: B
authors.lastname: Gipson
authors.forename: Henning
authors.initials: H
authors.lastname: Stahlberg
authors.forename: Crina M
authors.initials: CM
authors.lastname: Nimigean
mesh_terms: D000595:Amino Acid Sequence; D003461:Crystallography; D000242:Cyclic AMP / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015221:Potassium Channels / Q000737:chemistry*; D011487:Protein Conformation; D012231:Rhizobium / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D015221:Potassium Channels; D000242:Cyclic AMP