Exchange of Conduction Pathways Between Two Related K ⁺ Channels

Abstract

The structure of the ion conduction pathway or pore of voltage-gated ion channels is unknown, although the linker between the membrane spanning segments S5 and S6 has been suggested to form part of the pore in potassium channels. To test whether this region controls potassium channel conduction, a 21-amino acid segment of the S5-S6 linker was transplanted from the voltage-activated potassium channel NGK2 to another potassium channel DRK1, which has very different pore properties. In the resulting chimeric channel, the single channel conductance and blockade by external and internal tetraethylammonium (TEA) ion were characteristic of the donor NGK2 channel. Thus, this 21-amino acid segment controls the essential biophysical properties of the pore and may form the conduction pathway of these potassium channels.

Design of a functional calcium channel protein: Inferences about an ion channel‐forming motif derived from the primary structure of voltage‐gated calcium channels

“…The H5 segment, confined to the loop between predicted transmembrane segments S5 and S6 ( Fig. 1 A), is postulated to adopt a membrane-spanning &hairpin conformation and to modulate ionic selectivity (Hartmann et al, 1991;Pusch et al, 1991;Yellen et al, 1991;Yool & Schwartz, 1991;Heinemann et al, 1992). For consistency, all sequences are from the fourth homologous repeat (Fig.…”

“…The sequence of IVH5 was selected based on alignments with potassium and sodium channels for which site-directed mutagenesis data are available (Hartmann et al, 1991;Pusch et al, 1991;Yellen et al, 1991;Yool & Schwartz, 1991;Heinemann et al, 1992;Kim et al, 1993). Secondary structure prediction algorithms do not identify H5 as a potential &hairpin, the structure postulated originally for potassium channel H5 segments; mainly random conformation and turns are predicted for this segment.…”

Alternative Splicing in the Pore-Forming Region ofshakerPotassium Channels

“…The P region is postulated to form a loop structure that extends toward the central pore region, with the selectivity filter formed by the loops of the four subunits (MacK innon, 1995;Gross and MacKinnon, 1996;Ranganathan et al, 1996). E xtensive site-directed mutagenesis studies have been performed in the pore-forming region of Drosophila shak er to determine which residues are critical to channel f unction (MacK innon and Miller, 1989;MacKinnon and Yellen, 1990;Hartmann et al, 1991;Yellen et al, 1991;Yool and Schwarz, 1991;Heginbotham and MacKinnon, 1992). On the basis of these earlier results, it appears that many of the biophysical differences we observed between the pore I and II forms of Panulirus shaker arise from the addition of the positive charge at residue 407, which is threonine in pore I and positively charged arginine in pore II.…”

“…In Drosophila, all of these splice variants share a common conserved core region, which extends from before the first transmembrane region (S1) to the end of the pore-forming P region (Kamb et al, 1988;Pongs et al, 1988;Schwarz et al, 1988). Ion flux occurs through the P region, and site-directed mutagenesis of the amino acid sequence of this region has important functional consequences (MacKinnon et al, 1988;MacKinnon and Miller, 1989;MacKinnon and Yellen, 1990;Hartmann et al, 1991;Yellen et al, 1991;Yool and Schwarz, 1991;Heginbotham and MacKinnon, 1992). The P region forms a loop that extends into the center of the pore, with the four pore loops of the subunits forming the selectivity filter (MacKinnon, 1995;Gross and MacKinnon, 1996;Ranganathan et al, 1996).…”

Site-directed Glycosylation Tagging of Functional Kir2.1 Reveals That the Putative Pore-forming Segment Is Extracellular

“…Voltage-dependent K ϩ channels, Kvs, have a highly homologous H5 segment that appears to be the major pore determinant (see Fig. 1B) (7)(8)(9)(10). H5 contains eight highly conserved residues and has been proposed as the selectivity filter of K ϩ channels (see Fig.…”