The S4–S5 loop contributes to the ion-selective pore of potassium channels

Mutagenesis experiments on voltage-gated K+ channels have suggested that the ion-selective pore is comprised mostly of H5 segments. To see whether regions outside of the H5 segment might also contribute to the pore structure, we have studied the effect of single amino acid substitutions in the segment that connects the S4 and S5 putative transmembrane segments (S4-S5 loop) on various permeation properties of Shaker K+ channels. Mutations in the S4-S5 loop alter the Rb+ selectivity, the single-channel K+ and Rb+ conductances, and the sensitivity to open channel block produced by intracellular tetraethylammonium ion, Ba2+, and Mg2+. The block of Shaker K+ channels by intracellular Mg2+ is surprising, but is reminiscent of the internal Mg2+ blockade of inward rectifier K+ channels. The results suggest that the S4-S5 loop constitutes part of the ion-selective pore. Thus, the S4-S5 loop and the H5 segment are likely to contribute to the long pore characteristic of voltage-gated K+ channels.

[1]  R. MacKinnon,et al.  A functional connection between the pores of distantly related ion channels as revealed by mutant K+ channels. , 1992, Science.

[2]  W. Stühmer,et al.  Calcium channel characteristics conferred on the sodium channel by single mutations , 1992, Nature.

[3]  H. Guy,et al.  Atomic scale structure and functional models of voltage-gated potassium channels. , 1992, Biophysical journal.

[4]  Yuh Nung Jan,et al.  Evidence for the formation of heteromultimeric potassium channels in Xenopus oocytes , 1990, Nature.

[5]  T. Schwarz,et al.  Alteration of ionic selectivity of a K+ channel by mutation of the H5 region , 1991, Nature.

[6]  W. Almers,et al.  Repulsion between tetraethylammonium ions in cloned voltage-gated potassium channels , 1992, Neuron.

[7]  R. North,et al.  Interaction between tetraethylammonium and amino acid residues in the pore of cloned voltage-dependent potassium channels. , 1991, The Journal of biological chemistry.

[8]  B. Hille.  Ionic channels of excitable membranes , 2001 .

[9]  M. Moskovits,et al.  Order-Disorder Transition in Polycrystalline C60 Films , 1993, Science.

[10]  Y. Jan,et al.  Alteration of voltage-dependence of Shaker potassium channel by mutations in the S4 sequence , 1991, Nature.

[11]  A. Brown,et al.  A single nonpolar residue in the deep pore of related K+ channels acts as a K+:Rb+ conductance switch. , 1992, Biophysical journal.

[12]  C. Miller,et al.  1990: annus mirabilis of potassium channels , 1991, Science.

[13]  G. Schulz,et al.  Molecular architecture and electrostatic properties of a bacterial porin. , 1991, Science.

[14]  B. Hille,et al.  Potassium channels as multi-ion single-file pores , 1978, The Journal of general physiology.

[15]  Yoshihiro Kubo,et al.  Primary structure and functional expression of a mouse inward rectifier potassium channel , 1993, Nature.

[16]  E. Liman,et al.  Voltage-sensing residues in the S4 region of a mammalian K+ channel , 1991, Nature.

[17]  K. Lindpaintner,et al.  Incremental reductions of positive charge within the S4 region of a voltage-gated K+ channel result in corresponding decreases in gating charge , 1992, Neuron.

[18]  A. Woodhull,et al.  Ionic Blockage of Sodium Channels in Nerve , 1973, The Journal of general physiology.

[19]  C. Vandenberg.  Inward rectification of a potassium channel in cardiac ventricular cells depends on internal magnesium ions. , 1987, Proceedings of the National Academy of Sciences of the United States of America.

[20]  R. MacKinnon,et al.  Mutations affecting internal TEA blockade identify the probable pore-forming region of a K+ channel , 1991, Science.

[21]  A. Brown,et al.  Exchange of conduction pathways between two related K+ channels , 1991, Science.

[22]  T Hoshi,et al.  Biophysical and molecular mechanisms of Shaker potassium channel inactivation , 1990, Science.

[23]  A. Brown,et al.  Differences between the deep pores of K+ channels determined by an interacting pair of nonpolar amino acids , 1992, Neuron.

[24]  Christopher Miller,et al.  Hunting for the pore of voltage-gated channels , 1992, Current Biology.

[25]  A. Hodgkin,et al.  The potassium permeability of a giant nerve fibre , 1955, The Journal of physiology.

[26]  R. MacKinnon,et al.  Mutations affecting TEA blockade and ion permeation in voltage-activated K+ channels. , 1990, Science.

[27]  C. Armstrong.  Interaction of Tetraethylammonium Ion Derivatives with the Potassium Channels of Giant Axons , 1971, The Journal of general physiology.

[28]  R. MacKinnon.  New insights into the structure and function of potassium channels , 1991, Current Opinion in Neurobiology.

[29]  W. Jonathan Lederer,et al.  Cloning and expression of an inwardly rectifying ATP-regulated potassium channel , 1993, Nature.

[30]  H. Guy,et al.  Pursuing the structure and function of voltage-gated channels , 1990, Trends in Neurosciences.

[31]  H. Matsuda,et al.  Open‐state substructure of inwardly rectifying potassium channels revealed by magnesium block in guinea‐pig heart cells. , 1988, The Journal of physiology.

[32]  G. Eisenman,et al.  Cation selective glass electrodes and their mode of operation. , 1962, Biophysical journal.

[33]  R. MacKinnon,et al.  Mutant potassium channels with altered binding of charybdotoxin, a pore-blocking peptide inhibitor. , 1989, Science.

[34]  R. MacKinnon,et al.  Mapping the receptor site for charybdotoxin, a pore-blocking potassium channel inhibitor , 1990, Neuron.