Submitted to: Federation of European Biochemical Societies Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/21/2005
Publication Date: 5/9/2005
Citation: Pittman, J.K., Shigaki, T., Hirschi, K. 2005. Evidence of differential ph regulation of the arabidopsis vacuolar Ca2+/H+ antiporters CAX1 and CAX2. FEBS Letters. 579(12):2648-2656. Interpretive Summary: Some transporters work best under very acidic conditions. For example, the sour taste of some citruses are caused by particular transporters being active at low pH. Here we have examined what makes a transporter sensitive to the pH in the media. The next step will be to manipulate the pH optima. We may not want to get rid of the sour taste, but it will be nice to be able to some day modulate the taste!
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.