The structure of the prokaryotic cyclic nucleotide-modulated potassium channel MloK1 at 16 A resolution

Structure. 2007 Sep;15(9):1053-64. doi: 10.1016/j.str.2007.06.020.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Crystallography
  • Cyclic AMP / metabolism*
  • Microscopy, Electron, Transmission
  • Models, Molecular
  • Molecular Sequence Data
  • Potassium Channels / chemistry*
  • Protein Conformation
  • Rhizobium / chemistry*
  • Sequence Homology, Amino Acid


  • Potassium Channels
  • Cyclic AMP