Submitted to: Federation of European Biochemical Societies Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/21/2005
Publication Date: 4/9/2005
Citation: Pittman, J.K., Shigaki, T., Hirschi, K. 2005. Evidence of differential ph regulation of the arabidopsis vacuolar ca2+/h+ antiporters cax1 and cax2. Federation of European Biochemical Societies Letters. 579(12):2648-2656. Interpretive Summary: We report here how a particular metal transporter is regulated by environmental factors such as the concentration of protons in the media. Understanding this type of regulation is important if we are to eventually express these transporters in plants to cleanse soils of pollutants (toxic metals) through a process termed phytoremediation.
Technical 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.