title: Characterization of Arabidopsis Ca2+/H+ exchanger CAX3.
abstract: Plant calcium (Ca(2+)) gradients, millimolar levels in the vacuole and micromolar levels in the cytoplasm, are regulated in part by high-capacity vacuolar cation/H(+) exchangers (CAXs). Several CAX transporters, including CAX1, appear to contain an approximately 40-amino acid N-terminal regulatory region (NRR) that modulates transport through N-terminal autoinhibition. Deletion of the NRR from several CAXs (sCAX) enhances function in plant and yeast expression assays; however, to date, there are no functional assays for CAX3 (or sCAX3), which is 77% identical and 91% similar in sequence to CAX1. In this report, we create a series of truncations in the CAX3 NRR and demonstrate activation of CAX3 in both yeast and plants by truncating a large portion (up to 90 amino acids) of the NRR. Experiments with endomembrane-enriched vesicles isolated from yeast expressing activated CAX3 demonstrate that the gene encodes Ca(2+)/H(+) exchange with properties distinct from those of CAX1. The phenotypes produced by activated CAX3-expressing in transgenic tobacco lines are also distinct from those produced by sCAX1-expressing plants. These studies demonstrate shared and unique aspects of CAX1 and CAX3 transport and regulation.
authors.affiliation: United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, 1100 Bates Street, Houston, Texas 77030, United States.
authors.forename: Murli
authors.initials: M
authors.lastname: Manohar
authors.forename: Toshiro
authors.initials: T
authors.lastname: Shigaki
authors.forename: Hui
authors.initials: H
authors.lastname: Mei
authors.forename: Sunghun
authors.initials: S
authors.lastname: Park
authors.forename: Joy
authors.initials: J
authors.lastname: Marshall
authors.forename: Jonathan
authors.initials: J
authors.lastname: Aguilar
authors.forename: Kendal D
authors.initials: KD
authors.lastname: Hirschi
mesh_terms: D017920:Antiporters / Q000737:chemistry* / Q000235:genetics; D017360:Arabidopsis / Q000737:chemistry* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics; D001692:Biological Transport / Q000235:genetics; D002118:Calcium / Q000737:chemistry*; D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics; D006859:Hydrogen / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D014026:Nicotiana / Q000235:genetics
chemical_list: D017920:Antiporters; D029681:Arabidopsis Proteins; C506406:CAX3 protein, Arabidopsis; D027682:Cation Transport Proteins; D010446:Peptide Fragments; C027614:calcium-hydrogen antiporters; D006859:Hydrogen; D002118:Calcium