Structural determinants of Ca2+ transport in the Arabidopsis H+/Ca2+ antiporter CAX1

J Biol Chem. 2001 Nov 16;276(46):43152-9. doi: 10.1074/jbc.M106637200. Epub 2001 Sep 18.


Ca(2+) levels in plants, fungi, and bacteria are controlled in part by H(+)/Ca(2+) exchangers; however, the relationship between primary sequence and biological activity of these transporters has not been reported. The Arabidopsis H(+)/cation exchangers, CAX1 and CAX2, were identified by their ability to suppress yeast mutants defective in vacuolar Ca(2+) transport. CAX1 has a much higher capacity for Ca(2+) transport than CAX2. An Arabidopsis thaliana homolog of CAX1, CAX3, is 77% identical (93% similar) and, when expressed in yeast, localized to the vacuole but did not suppress yeast mutants defective in vacuolar Ca(2+) transport. Chimeric constructs and site-directed mutagenesis showed that CAX3 could suppress yeast vacuolar Ca(2+) transport mutants if a nine-amino acid region of CAX1 was inserted into CAX3 (CAX3-9). Biochemical analysis in yeast showed CAX3-9 had 36% of the H(+)/Ca(2+) exchange activity as compared with CAX1; however, CAX3-9 and CAX1 appear to differ in their transport of other ions. Exchanging the nine-amino acid region of CAX1 into CAX2 doubled yeast vacuolar Ca(2+) transport but did not appear to alter the transport of other ions. This nine-amino acid region is highly variable among the plant CAX-like transporters. These findings suggest that this region is involved in CAX-mediated Ca(2+) specificity.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Amino Acids / chemistry
  • Antiporters / chemistry*
  • Antiporters / metabolism*
  • Arabidopsis / chemistry*
  • Biological Transport
  • Calcium / metabolism*
  • Calcium-Binding Proteins / chemistry*
  • Calcium-Binding Proteins / metabolism*
  • Cation Transport Proteins*
  • Cations
  • Cell Membrane / metabolism
  • Dose-Response Relationship, Drug
  • Hydrogen / metabolism*
  • Hydrogen-Ion Concentration
  • Kinetics
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Protein Binding
  • Protein Conformation
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Signal Transduction
  • Structure-Activity Relationship
  • Time Factors
  • Vacuoles / metabolism


  • Amino Acids
  • Antiporters
  • Calcium-Binding Proteins
  • Cation Transport Proteins
  • Cations
  • Recombinant Fusion Proteins
  • calcium-hydrogen antiporters
  • Hydrogen
  • Calcium