Anomalous mole fraction effect induced by mutation of the H5 pore region in the Shaker K+ channel.
Mutagenesis of the H5 region of the Shaker K+ channel has provided strong evidence that these amino acids form a major portion of the ionic pore. We have previously observed that a single-site mutation (T441S) in this region increased the apparent relative permeability of the channel to NH4+. We now report that this increased relative permeability to NH4+ is sensitive to small changes in external K+ in a pattern consistent with an anomalous mole fraction effect. The effect is not apparent in the wild-type channel. These findings, in combination with other studies showing effects of this particular mutation on the binding of tetraethylammonium and hydroxylamine, support the hypothesis that T441S alters the affinity of a putative ion binding site for NH4+ and ammonium derivatives. The mutation T441S alters ionic selectivity and reveals the multi-ion nature of the mutant Shaker K+ channel.
Department of Physiology, University of Arizona College of Medicine, Tucson 85724-5051, USA.
A J
AJ
Yool
T L
TL
Schwarz
D000818:Animals; D004553:Electric Conductivity; D015640:Ion Channel Gating; D008564:Membrane Potentials; D016297:Mutagenesis, Site-Directed; D009865:Oocytes; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D011188:Potassium / Q000502:physiology; D015221:Potassium Channels / Q000737:chemistry / Q000502:physiology*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
D015221:Potassium Channels; D000644:Quaternary Ammonium Compounds; D011993:Recombinant Fusion Proteins; D011188:Potassium