High-Resolution Cryoelectron Microscopy Structure of the Cyclic Nucleotide-Modulated Potassium Channel MloK1 in a Lipid Bilayer

• DOI: 10.1016/j.str.2017.11.012
• Publication Date: 2017-12-14T11:45:18Z
• Authors: Julia Kowal; Nikhil Biyani; Mohamed Chami; Sebastian Scherer; Andrzej J. Rzepiela; Paul Baumgartner; Vikrant Upadhyay; Crina M. Nimigean; Henning Stahlberg
• Keywords: Models, Molecular; 0303 health sciences; Binding Sites; Potassium Channels; Cryoelectron Microscopy; Genetic Vectors; Lipid Bilayers; Mesorhizobium; Gene Expression; Ion Channels; 03 medical and health sciences; Bacterial Proteins; Potassium Channels, Voltage-Gated; Cyclic AMP; Escherichia coli; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; Image Processing, Computer-Assisted; Potassium; Cloning, Molecular; Caenorhabditis elegans Proteins; Ion Channel Gating; Protein Binding

Eukaryotic cyclic nucleotide-modulated channels perform their diverse physiological roles by opening and closing their pores to ions in response to cyclic nucleotide binding. We here present a structural model for the cyclic nucleotide-modulated potassium channel homolog from Mesorhizobium loti, MloK1, determined from 2D crystals in the presence of lipids. Even though crystals diffract electrons to only ∼10 Å, using cryoelectron microscopy (cryo-EM) and recently developed computational methods, we have determined a 3D map of full-length MloK1 in the presence of cyclic AMP (cAMP) at ∼4.5 Å isotropic 3D resolution. The structure provides a clear picture of the arrangement of the cyclic nucleotide-binding domains with respect to both the pore and the putative voltage sensor domains when cAMP is bound, and reveals a potential gating mechanism in the context of the lipid-embedded channel.