Mechanism of anionic conduction across ClC.
ClC chloride channels are voltage-gated transmembrane proteins that have been associated with a wide range of regulatory roles in vertebrates. To accomplish their function, they allow small inorganic anions to efficiently pass through, while blocking the passage of all other particles. Understanding the conduction mechanism of ClC has been the subject of many experimental investigations, but until now, the detailed dynamic mechanism was not known despite the availability of crystallographic structures. We investigate Cl(-) conduction by means of an all-atom molecular dynamics simulation of the ClC channel in a membrane environment. Based on our simulation results, we propose a king-of-the-hill mechanism for permeation, in which a lone ion bound to the center of the ClC pore is pushed out by a second ion that enters the pore and takes its place. Although the energy required to extract the single central ion from the pore is enormous, by resorting to this two-ion process, the largest free energy barrier for conduction is reduced to 4 kcal/mol. At the narrowest part of the pore, residues Tyr-445 and Ser-107 stabilize the central ion. There, the bound ion blocks the pore, disrupting the formation of a continuous water file that could leak protons, possibly preventing the passage of uncharged solutes.
Cohen
Jordi
J
Department of Physics and Beckman Institute, University of Illinois, Urbana, Illinois 61801, USA.
Schulten
Klaus
K
D000596:Amino Acids / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D001665:Binding Sites; D018118:Chloride Channels / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D003198:Computer Simulation; D004553:Electric Conductivity; D015640:Ion Channel Gating; D008563:Membrane Lipids / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D010539:Permeability; D010714:Phosphatidylethanolamines / Q000737:chemistry; D016062:Porosity; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012475:Salmonella / Q000378:metabolism; D055672:Static Electricity; D013329:Structure-Activity Relationship; D014867:Water / Q000737:chemistry
D000596:Amino Acids; D000838:Anions; D018118:Chloride Channels; D008563:Membrane Lipids; D010714:Phosphatidylethanolamines; D014867:Water; C057561:1-palmitoyl-2-oleoylphosphatidylethanolamine; D002713:Chlorine