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

Pascal Mäser, Yoshihiro Hosoo, Shinobu Goshima, Tomoaki Horie, Brendan Eckelman, Katsuyuki Yamada, Kazuya Yoshida, Evert P. Bakker, Atsuhiko Shinmyo, Shigetoshi Oiki, Julian I. Schroeder, Nobuyuki Uozumi

Research output: Contribution to journalArticlepeer-review

193 Citations (Scopus)

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 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.

Original languageEnglish
Pages (from-to)6428-6433
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume99
Issue number9
DOIs
Publication statusPublished - 2002 Apr 30

ASJC Scopus subject areas

  • General

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