title: Amino terminus and the first four membrane-spanning segments of the Arabidopsis K+ channel KAT1 confer inward-rectification property of plant-animal chimeric channels.
abstract: The Arabidopsis hyperpolarization-activated (inward-rectifying) K+ channel KAT1 is structurally more similar to animal depolarization-activated (outward-rectifying) K+ channels than to animal hyperpolarization-activated K+ channels. To gain insight into the structural basis for the opposite voltage dependences of plant inward-rectifying and animal outward-rectifying K+ channels, we constructed recombinant chimeric channels between the hyperpolarization-activated K+ channel KAT1 and a Xenopus depolarization-activated K+ channel. We report here that two of the chimeric constructs, which contain the first third of the KAT1 sequence, including the first four membrane-spanning segments (S1-S4) and the linker sequence between the fourth and fifth membrane-spanning segments, express functional channels that retain activation by hyperpolarization, but not depolarization. These two chimeric channels are no longer selective for K+. The chimeras are selective for cations over anions and are permeable to Ca2+. Therefore, unlike animal hyperpolarization-activated K+ channels, in which the carboxyl terminus is important for inward rectification induced by Mg2+ and polyamine block, the plant KAT1 channel has its major determinants for inward rectification in the amino-terminal region, which ends at the end of the S4-S5 linker.
authors.affiliation: Department of Biology, University of California at San Diego, La Jolla 92093-0116, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Cao
authors.forename: N M
authors.initials: NM
authors.lastname: Crawford
authors.forename: J I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004533:Egtazic Acid / Q000031:analogs & derivatives; D007202:Indicators and Reagents; D017136:Ion Transport; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D015221:Potassium Channels / Q000235:genetics* / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014981:Xenopus
chemical_list: D029681:Arabidopsis Proteins; D002712:Chlorides; D018076:DNA, Complementary; D007202:Indicators and Reagents; C501210:KAT1 protein, Arabidopsis; D010940:Plant Proteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011993:Recombinant Fusion Proteins; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium