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Glycine residues in potassium channel-like selectivity filters determine potassium selectivity in four-loop-per-subunit HKT transporters from plants.


ABSTRACT: 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 mediates 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 AtHKT1/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.

SUBMITTER: Maser P 

PROVIDER: S-EPMC122965 | biostudies-literature | 2002 Apr

REPOSITORIES: biostudies-literature

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Glycine residues in potassium channel-like selectivity filters determine potassium selectivity in four-loop-per-subunit HKT transporters from plants.

Mäser Pascal P   Hosoo Yoshihiro Y   Goshima Shinobu S   Horie Tomoaki T   Eckelman Brendan B   Yamada Katsuyuki K   Yoshida Kazuya K   Bakker Evert P EP   Shinmyo Atsuhiko A   Oiki Shigetoshi S   Schroeder Julian I JI   Uozumi Nobuyuki N  

Proceedings of the National Academy of Sciences of the United States of America 20020416 9


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 mediates Na(+)-coupled K(+) transport. Arabidopsis AtHKT1, however, transports only Na(+) in eukaryotic expression systems. To understand  ...[more]

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