Biophys J 89(1): 179-186

The Fast Gating Mechanism in ClC-0 Channels

^{Department of Theoretical Physics, Research School of Physical Sciences, The Australian National University, Canberra, Australia; and}^{Department of Chemistry, School of Biomedical and Chemical Sciences, The University of Western Australia, Crawley, Australia}

Address reprint requests to Ben Corry, Fax: 61-8-6488-1005; E-mail: ua.ude.awu.mehcoeht@neb.

Received 2004 Sep 23; Accepted 2005 Apr 26.

Abstract

We investigate and then modify the hypothesis that a glutamate side chain acts as the fast gate in ClC-0 channels. We first create a putative open-state configuration of the prokaryotic ClC Cl^{channel using its crystallographic structure as a basis. Then, retaining the same pore shape, the prokaryotic ClC channel is converted to ClC-0 by replacing all the nonconserved polar and charged residues. Using this open-state channel model, we carry out molecular dynamics simulations to study how the glutamate side chain can move between open and closed configurations. When the side chain extends toward the extracellular end of the channel, it presents an electrostatic barrier to Cl}^{conduction. However, external Cl}^{ions can push the side chain into a more central position where, pressed against the channel wall, it does not impede the motion of Cl}^{ions. Additionally, a proton from a low-pH external solution can neutralize the extended glutamate side chain, which also removes the barrier to conduction. Finally, we use Brownian dynamics simulations to demonstrate the influence of membrane potential and external Cl}^{concentration on channel open probability.}

Abstract

Acknowledgments

The simulations were carried out on the Compaq AlphaServer SC at the APAC National Facility. Figs. 1 and and22 were created using the program VMD (22).

This work was supported by grants from the Australian Research Council, the National Health and Medical Research Council of Australia, and the Australian Partnership for Advanced Computing.

Acknowledgments

References

1. Jentsch, T. J., T. Friedrich, A. Schriever, and H. Yamada. 1999. The ClC chloride channel family. Pflugers Arch.437:783–795. [[PubMed]
2. Maduke, M., C. Miller, and J. A. Mindell. 2000. A decade of ClC chloride channels: structure, mechanism, and many unsettled questions. Annu. Rev. Biophys. Biomol. Struct.29:411–438. [[PubMed]
3. Fahlke, C. 2001. Ion permeation and selectivity in ClC-type chloride channels. Am. J. Physiol. Renal Physiol.280:F748–F757. [[PubMed]
4. Jentsch, T. J., V. Stein, F. Weinreich, and A. A. Zdebik. 2002. Molecular structure and physiological function of chloride channels. Physiol. Rev.82:503–568. [[PubMed]
5. Miller, C. 1982. Open-state substructure of single chloride channels from Torpedo electroplax. Phil. Trans. Roy. Soc. Lond. B. Biol. Sci.B299:401–411. [[PubMed]
6. Pusch, M., U. Ludewig, A. Rehfeldt, and T. J. Jentsch. 1995. Gating of the voltage-dependent chloride channel ClC-0 by the permeant anions. Nature.373:527–531. [[PubMed]
7. Chen, T.-Y., M.-F. Chen, and C.-W. Lin. 2003. Electrostatic control and chloride regulation of the fast gating of ClC-0 chloride channels. J. Gen. Physiol.122:641–651.
8. Chen, T.-Y., and C. Miller. 1996. Nonequilibrium gating and voltage dependence of the ClC-0 Cl^channel.J. Gen. Physiol.108:237–250.
9. Chen, M.-F., and T.-Y. Chen. 2001. Different fast-gate regulation by external Cl^{and H}^{of the muscle-type ClC chloride channels.}J. Gen. Physiol.118:23–32.
10. Dutzler, R., E. B. Campbell, and R. MacKinnon. 2003. Gating the selectivity filter in ClC chloride channels. Science.300:108–112. [[PubMed]
11. Dutzler, R., E. B. Campbell, M. Cadene, B. T. Chait, and R. MacKinnon. 2002. X-ray structure of a ClC chloride channel at 3.0 Å reveals the molecular basis of anion selectivity. Nature.415:287–294. [[PubMed]
12. Cohen, J., and K. Schulten. 2004. Mechanism of anionic conduction across ClC. Biophys. J.86:836–845.
13. Bostik, D. L., and M. L. Berkowitz. 2004. Exterior site occupancy infers chloride induced proton gating in a prokaryotic homolog of the ClC chloride channel. Biophys. J.87:1686–1696.
14. Accardi, A., and C. Miller. 2004. Secondary active transport mediated by a prokaryotic homologue of ClC Cl^channels.Nature.427:803–807. [[PubMed]
15. Estévez, R., B. C. Schroeder, A. Accardi, T. J. Jentsch, and M. Pusch. 2003. Conservation of chloride channel structure revealed by an inhibitor binding site in ClC-1. Neuron.38:47–59. [[PubMed]
16. Law, R. J., and M. S. Sansom. 2004. Homology modelling and molecular dynamics simulations: comparative studies of human aquaporin-1. Eur. Biophys. J.33:477–489. [[PubMed]
17. Brooks, B. R., R. E. Bruccoleri, B. D. Olafson, D. J. States, S. Swaminathan, and M. Karplus. 1983. CHARMM: a program for macromolecular energy, minimization, and dynamics calculations. J. Comput. Chem.4:187–217. [PubMed]
18. MacKerell, A. D. Jr., D. Bashford, M. Bellot, R. L. Dunbrack Jr., J. D. Evanseck, M. J. Field, S. Fisher, J. Gao, H. Guo, S. Ha, D. Joseph-McCarthy, L. Kuchnir, K. Kuczera, F. T. K. Lau, C. Mattos, S. Michnick, T. Ngo, D. T. Nguyen, B. Prodhom, W. E. Reiher III, B. Roux, M. Schlenkrich, J. C. Smith, R. Stote, J. Straub, M. Watanabe, J. Wiorkiewicz-Kuczera, D. Yin, and M. Karplus. 1998. All-atom empirical potential for molecular modeling and dynamics studies of proteins. J. Phys. Chem. B.102:3586–3616. [[PubMed]
19. Corry, B., M. O'Mara, and S. H. Chung. 2004. Conduction mechanisms of chloride ions in CLC-type channels. Biophys. J.86:846–860.
20. Corry, B., M. O'Mara, and S. H. Chung. 2004. Permeation dynamics of chloride ions in ClC-0 and ClC-1 channels. Chem. Phys. Lett.386:233–238. [PubMed]
21. Accardi, A., and M. Pusch. 2003. Conformational changes in the pore of ClC-0. J. Gen. Physiol.122:277–293.
22. Humphrey, W., A. Dalke, and K. Schulten. 1996. VMD—Visual molecular dynamics. J. Mol. Graph.14:33–38. [[PubMed]