Helical structure and packing orientation of the S2 segment in the Shaker K+ channel.
Six transmembrane segments, S1-S6, cluster around the central pore-forming region in voltage-gated K+ channels. To investigate the structural characteristics of the S2 segment in the Shaker K+ channel, we replaced each residue in S2 singly with tryptophan (or with alanine for the native tryptophan). All but one of the 23 Trp mutants expressed voltage-dependent K+ currents in Xenopus oocytes. The effects of the mutations were classified as being of low or high impact on channel gating properties. The periodicity evident in the effects of these mutations supports an alpha-helical structure for the S2 segment. The high- and low-impact residues cluster onto opposite faces of a helical wheel projection of the S2 segment. The low-impact face is also tolerant of single mutations to asparagine. All results are consistent with the idea that the low-impact face projects toward membrane lipids and that changes in S2 packing occur upon channel opening. We conclude that the S2 segment is a transmembrane alpha helix and that the high-impact face packs against other transmembrane segments in the functional channel.
Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, Massachusetts 02454, USA.
S A
SA
Monks
D J
DJ
Needleman
C
C
Miller
D000595:Amino Acid Sequence; D000818:Animals; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000502:physiology; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017354:Point Mutation / Q000235:genetics / Q000502:physiology; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D051637:Shaker Superfamily of Potassium Channels; D014364:Tryptophan / Q000737:chemistry; D014982:Xenopus laevis
D008055:Lipids; D015221:Potassium Channels; D011994:Recombinant Proteins; D051637:Shaker Superfamily of Potassium Channels; D014364:Tryptophan