Arabidopsis KEA2, a homolog of bacterial KefC, encodes a K+/H+ antiporter with a chloroplast transit peptide

Aranda-Sicilia, María Nieves, Cagnac, Olivier, Chanroj, Salil, Sze, Heven, Rodríguez-Rosales, María Pilar and Venema, Kees (2012) Arabidopsis KEA2, a homolog of bacterial KefC, encodes a K+/H+ antiporter with a chloroplast transit peptide. Biochimica et Biophysica Acta (BBA) - Biomembranes, 1818 9: 2362-2371. doi:10.1016/j.bbamem.2012.04.011


Author Aranda-Sicilia, María Nieves
Cagnac, Olivier
Chanroj, Salil
Sze, Heven
Rodríguez-Rosales, María Pilar
Venema, Kees
Title Arabidopsis KEA2, a homolog of bacterial KefC, encodes a K+/H+ antiporter with a chloroplast transit peptide
Formatted title
Arabidopsis KEA2, a homolog of bacterial KefC, encodes a K+/H+ antiporter with a chloroplast transit peptide
Journal name Biochimica et Biophysica Acta (BBA) - Biomembranes   Check publisher's open access policy
ISSN 0005-2736
Publication date 2012-09-01
Sub-type Article (original research)
DOI 10.1016/j.bbamem.2012.04.011
Open Access Status Not Open Access
Volume 1818
Issue 9
Start page 2362
End page 2371
Total pages 10
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Language eng
Subject 1303 Specialist Studies in Education
1307 Cell Biology
1304 Biophysics
Formatted abstract
KEA genes encode putative K+ efflux antiporters that are predominantly found in algae and plants but are rare in metazoa; however, nothing is known about their functions in eukaryotic cells. Plant KEA proteins show homology to bacterial K+ efflux (Kef) transporters, though two members in the Arabidopsis thaliana family, AtKEA1 and AtKEA2, have acquired an extra hydrophilic domain of over 500 residues at the amino terminus. We show that AtKEA2 is highly expressed in leaves, stems and flowers, but not in roots, and that an N-terminal peptide of the protein is targeted to chloroplasts in Arabidopsis cotyledons. The full-length AtKEA2 protein was inactive when expressed in yeast; however, a truncated AtKEA2 protein (AtsKEA2) lacking the N-terminal domain complemented disruption of the Na+(K+)/H+ antiporter Nhx1p to confer hygromycin resistance and tolerance to Na+ or K+ stress. To test transport activity, purified truncated AtKEA2 was reconstituted in proteoliposomes containing the fluorescent probe pyranine. Monovalent cations reduced an imposed pH gradient (acid inside) indicating AtsKEA2 mediated cation/H+ exchange with preference for K+ = Cs+ > Li+ > Na+. When a conserved Asp721 in transmembrane helix 6 that aligns to the cation binding Asp164 of Escherichia coli NhaA was replaced with Ala, AtsKEA2 was completely inactivated. Mutation of a Glu835 between transmembrane helix 8 and 9 in AtsKEA2 also resulted in loss of activity suggesting this region has a regulatory role. Thus, AtKEA2 represents the founding member of a novel group of eukaryote K+/H+ antiporters that modulate monovalent cation and pH homeostasis in plant chloroplasts or plastids.

Highlights
► Plant KEA proteins share high homology to bacterial KefC/B antiporters. ► Full‐length AtKEA2 is inactive in yeast. ► AtKEA2 without N-terminal domain complements yeast Nhx1p. ► Purified and reconstituted short AtKEA2 protein has K+/H+ exchange activity. ► Cation specificity of AtKEA2 is similar to EcKefC.
Keyword Arabidopsis
K+/H+ antiport
Potassium transport
Reconstitution
Yeast
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Agriculture and Food Sciences
 
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