Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2002
Publication Date: 7/19/2002
Citation: Pittman,J.K., Shigaki,T., Cheng,N.H., Hirschi,K.D. 2002. Mechanism of N-terminal autoinhibition in the Arabidopsis Ca(2+)/H(+) antiporter CAX1. Journal of Biological Chemistry. 277(29):26452-26459. Interpretive Summary: A small weed, termed Arabidopsis, can be used as a model to understand complex biological processes in agriculturally important plants. In this study, we have used Arabidopsis to analyze the regulation of calcium transporters. For the first time, we have shown that specific types of calcium transporters are tightly controlled. These results will form a foundation for future studies in agriculturally important crops. Eventually, we hope to manipulate these calcium transporters to increase the calcium levels in important crops. These engineered crops will allow greater consumption of important nutrients by consumers.
Technical Abstract: Regulation of Ca2+/H+ antiporters may be an important component in determining the duration and amplitude of cytosolic Ca2+ oscillations. Previously, the Arabidopsis Ca2+/H+ transporter, CAX1 (cation exchanger 1), was identified by its ability to suppress yeast mutants defective in vacuolar Ca2+ transport. Recently, a 36 amino acid N-terminal regulatory region on CAX1 has been identified that inhibits CAX1-mediated Ca2+/H+ antiport. Here we show that a synthetic peptide designed against the CAX1 36 amino acids inhibited Ca2+/H+ transport mediated by an N-terminal truncated CAX1 but did not inhibit Ca2+ transport by other Ca2+/H+ antiporters. Ca2+/H+ antiport activity measured from vacuolar-enriched membranes of Arabidopsis root was also inhibited by the CAX1 peptide. Through analyzing CAX chimeric constructs, the region of interaction of the N-terminal regulatory region was mapped to include 7 amino acids (residues 56 to 62) within CAX1. The CAX1 N-terminal regulatory region was shown to physically interact with this 7 amino acid region by yeast two-hybrid analysis. Mutagenesis of amino acids within the N-terminal regulatory region implicated several residues as being essential for regulation. These findings describe a unique mode of antiporter autoinhibition and demonstrate the first detailed mechanisms for the regulation of a Ca2+/H+ antiporter from any organism.