Interactive domains between pore loops of the yeast K+ channel TOK1 associate with extracellular K+ sensitivity.
Gating of the outward-rectifying K+ channel TOK1 of Saccharomyces cerevisiae is controlled by membrane voltage and extracellular K+ concentration. Previous studies identified two kinetically distinct effects of K+, and site-mutagenic analysis associated these K+-dependencies with domains of the extracellular turrets of the channel protein. We have mapped the TOK1 pore domains to extant K+ channel crystal structures to target additional residues contributing to TOK1 gating. Leu270, located in the first pore domain of TOK1, was found to be critical for gating and its K+ sensitivity. Analysis of amino acid substitutions indicated that spatial position of the polypeptide backbone is a primary factor determining gating sensitivity to K+. The strongest effects, with L270Y, L270F and L270W, led to more than a 30-fold decrease in apparent K+ affinity and an inversion in the apparent K+-dependence of voltage-dependent gating compared with the wild-type current. A partial rescue of wild-type gating was obtained on substitution in the second pore domain with the double mutant L270D/A428Y. These, and additional results, demarcate extracellular domains that are associated with the K+-sensitivity of TOK1 and they offer primary evidence for a synergy in gating between the two pore domains of TOK1, demonstrating an unexpected degree of long-distance interaction across the mouth of the K+ channel.
Johansson
Ingela
I
Laboratory of Plant Physiology and Biophysics, IBLS - Plant Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, UK.
Blatt
Michael R
MR
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D004789:Enzyme Activation; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*; D014982:Xenopus laevis
D015221:Potassium Channels; D029701:Saccharomyces cerevisiae Proteins; C095220:TOK1 protein, S cerevisiae; D011188:Potassium