structural, functional, and computational analysis suggests pore flexibility as the base for the poor selectivity of CNG channels

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-07, Vol.112 (27), p.E3619-E3628
• Main Authors: Napolitano, Luisa Maria Rosaria, Ina Bisha, Matteo De March, Arin Marchesi, Manuel Arcangeletti, Nicola Demitri, Monica Mazzolini, Alex Rodriguez, Alessandra Magistrato, Silvia Onesti, Alessandro Laio, Vincent Torre
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biological Sciences; cations; Cations, Monovalent - metabolism; Cattle; Cesium - metabolism; CNG channels; Crystallography; Crystallography, X-Ray; Cyclic Nucleotide-Gated Cation Channels - chemistry; Cyclic Nucleotide-Gated Cation Channels - genetics; Cyclic Nucleotide-Gated Cation Channels - metabolism; electrophysiology; Female; Ion Channel Gating - genetics; Ion Channel Gating - physiology; ion channels; Ion Transport - drug effects; MD simulations; Membrane Potentials - drug effects; Membrane Potentials - physiology; molecular dynamics; Molecular Dynamics Simulation; Molecular Sequence Data; Mutant Proteins - chemistry; Mutant Proteins - metabolism; Mutation, Missense; Oocytes - metabolism; Oocytes - physiology; Patch-Clamp Techniques; PNAS Plus; pore flexibility; potassium; Protein Conformation; Sequence Homology, Amino Acid; Simulation; sodium; Sodium - metabolism; X-ray crystallography; X-ray diffraction; X-rays; Xenopus laevis
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1503334112

Cyclic nucleotide-gated (CNG) ion channels, despite a significant homology with the highly selective K ⁺ channels, do not discriminate among monovalent alkali cations and are permeable also to several organic cations. We combined electrophysiology, molecular dynamics (MD) simulations, and X-ray crystallography to demonstrate that the pore of CNG channels is highly flexible. When a CNG mimic is crystallized in the presence of a variety of monovalent cations, including Na ⁺, Cs ⁺, and dimethylammonium (DMA ⁺), the side chain of Glu66 in the selectivity filter shows multiple conformations and the diameter of the pore changes significantly. MD simulations indicate that Glu66 and the prolines in the outer vestibule undergo large fluctuations, which are modulated by the ionic species and the voltage. This flexibility underlies the coupling between gating and permeation and the poor ionic selectivity of CNG channels.