TY - JOUR
T1 - Glycine residues in potassium channel-like selectivity filters determine potassium selectivity in four-loop-per-subunit HKT transporters from plants
AU - Mäser, Pascal
AU - Hosoo, Yoshihiro
AU - Goshima, Shinobu
AU - Horie, Tomoaki
AU - Eckelman, Brendan
AU - Yamada, Katsuyuki
AU - Yoshida, Kazuya
AU - Bakker, Evert P.
AU - Shinmyo, Atsuhiko
AU - Oiki, Shigetoshi
AU - Schroeder, Julian I.
AU - Uozumi, Nobuyuki
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2002/4/30
Y1 - 2002/4/30
N2 - Plant HKT proteins comprise a family of cation transporters together with prokaryotic KtrB, TrkH, and KdpA transporter subunits and fungal Trk proteins. These transporters contain four loop domains in one polypeptide with a proposed distant homology to K+ channel selectivity filters. Functional expression in yeast and Xenopus oocytes revealed that wheat HKT1 ediates Na+-coupled K+ transport. Arabidopsis AtHKT1, however, transports only Na+ in eukaryotic expression systems. To understand the molecular basis of this difference we constructed a series of AtHKTI/HKT1 chimeras and introduced point mutations to AtHKT1 and wheat HKT1 at positions predicted to be critical for K+ selectivity. A single-point mutation, Ser-68 to glycine, was sufficient to restore K+ permeability to AtHKT1. The reverse mutation in HKT1, Gly-91 to serine, abrogated K+ permeability. This glycine in P-loop A of AtHKT1 and HKT1 can be modeled as the first glycine of the K+ channel selectivity filter GYG motif. The importance of such filter glycines for K+ selectivity was confirmed by interconversion of Ser-88 and Gly-88 in the rice paralogues OsHKT1 and OsHKT2. Surprisingly, all HKT homologues known from dicots have a serine at the filter position in P-loop A, suggesting that these proteins function mainly as Na+ transporters in plants and that Na+/K+ symport in HKT proteins is associated with a glycine in the filter residue. These data provide experimental evidence that the glycine residues in selectivity filters of HKT proteins are structurally related to those of K+ channels.
AB - Plant HKT proteins comprise a family of cation transporters together with prokaryotic KtrB, TrkH, and KdpA transporter subunits and fungal Trk proteins. These transporters contain four loop domains in one polypeptide with a proposed distant homology to K+ channel selectivity filters. Functional expression in yeast and Xenopus oocytes revealed that wheat HKT1 ediates Na+-coupled K+ transport. Arabidopsis AtHKT1, however, transports only Na+ in eukaryotic expression systems. To understand the molecular basis of this difference we constructed a series of AtHKTI/HKT1 chimeras and introduced point mutations to AtHKT1 and wheat HKT1 at positions predicted to be critical for K+ selectivity. A single-point mutation, Ser-68 to glycine, was sufficient to restore K+ permeability to AtHKT1. The reverse mutation in HKT1, Gly-91 to serine, abrogated K+ permeability. This glycine in P-loop A of AtHKT1 and HKT1 can be modeled as the first glycine of the K+ channel selectivity filter GYG motif. The importance of such filter glycines for K+ selectivity was confirmed by interconversion of Ser-88 and Gly-88 in the rice paralogues OsHKT1 and OsHKT2. Surprisingly, all HKT homologues known from dicots have a serine at the filter position in P-loop A, suggesting that these proteins function mainly as Na+ transporters in plants and that Na+/K+ symport in HKT proteins is associated with a glycine in the filter residue. These data provide experimental evidence that the glycine residues in selectivity filters of HKT proteins are structurally related to those of K+ channels.
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U2 - 10.1073/pnas.082123799
DO - 10.1073/pnas.082123799
M3 - Article
C2 - 11959905
AN - SCOPUS:11144357502
VL - 99
SP - 6428
EP - 6433
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
SN - 0027-8424
IS - 9
ER -