title: Evidence of differential pH regulation of the Arabidopsis vacuolar Ca2+/H+ antiporters CAX1 and CAX2.
abstract: The Arabidopsis Ca(2+)/H(+) antiporters cation exchanger (CAX) 1 and 2 utilise an electrochemical gradient to transport Ca(2+) into the vacuole to help mediate Ca(2+) homeostasis. Previous whole plant studies indicate that activity of Ca(2+)/H(+) antiporters is regulated by pH. However, the pH regulation of individual Ca(2+)/H(+) antiporters has not been examined. To determine whether CAX1 and CAX2 activity is affected by pH, Ca(2+)/H(+) antiport activity was measured in vacuolar membrane vesicles isolated from yeast heterologously expressing either transporter. Ca(2+) transport by CAX1 and CAX2 was regulated by cytosolic pH and each transporter had a distinct cytosolic pH profile. Screening of CAX1/CAX2 chimeras identified an amino acid domain within CAX2 that altered the pH-dependent Ca(2+) transport profile so that it was almost identical to the pH profile of CAX1. Results from mutagenesis of a specific His residue within this domain suggests a role for this residue in pH regulation.
authors.affiliation: Faculty of Life Sciences, University of Manchester, UK. jon.pittman@manchester.ac.uk
authors.forename: Jon K
authors.initials: JK
authors.lastname: Pittman
authors.forename: Toshiro
authors.initials: T
authors.lastname: Shigaki
authors.forename: Kendal D
authors.initials: KD
authors.lastname: Hirschi
mesh_terms: D017920:Antiporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000737:chemistry*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry; D006639:Histidine / Q000737:chemistry; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics; D014617:Vacuoles / Q000378:metabolism
chemical_list: D017920:Antiporters; D029681:Arabidopsis Proteins; D011994:Recombinant Proteins; D006639:Histidine; D006859:Hydrogen; D002118:Calcium