Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2003
Publication Date: 10/1/2002
Citation: PITTMAN, J.K., SREEVIDYA, C.S., SHIGAKI, T., UEOKA-NAKANISHI, H., HIRSCHI, K. DISTINCT N-TERMINAL REGULATORY DOMAINS OF CA2+/H+ ANTIPORTERS. PLANT PHYSIOLOGY. 2002. v. 130. p. 1054-1062. Interpretive Summary: The ability to manipulate calcium levels in plants to improve human nutrition requires an understanding of how plants control calcium movement. In this study, we have analyzed how different plants control calcium levels. We have analyzed the regulation of calcium transporters from various different plants. These findings will help us engineer a plants ability to move nutrients into edible plants to improve human nutrition. Eventually, these types of approaches will limit the incidence of diseases like osteoporosis.
Technical Abstract: The regulation of intracellular Ca2+ levels is achieved in part by high capacity vacuolar Ca2+/H+ antiporters. An N-terminal regulatory region (NRR) on the Arabidopsis Ca2+/H+ antiporter CAX1 (cation exchanger 1) has previously been shown to regulate Ca2+ transport by a mechanism of N-terminal autoinhibition. The regulation of other CAX transporters was examined in order to determine whether such a mechanism was common for Ca2+/H+ antiporters. Here we show that N-terminal extensions also regulate the activity of other CAX transporters yet the regulatory elements appear specific for each. Mung bean VCAX1 is active despite having an extended N-terminal tail. Removal of the VCAX1 N-terminus significantly increased Ca2+/H+ antiport activity. Biochemical analysis of VCAX1 expressed in Saccharomyces cerevisiae showed that truncated VCAX1 had approximately 70% greater antiport activity compared to full-length VCAX1. The N-terminus of Arabidopsis CAX3 was also shown to contain an NRR. A synthetic peptide corresponding to the NRR of CAX1, which can strongly inhibit Ca2+ transport by CAX1, could not significantly inhibit Ca2+ transport by truncated VCAX1. Additions of either the CAX3 or VCAX1 regulatory regions to the N-terminus of an N-terminal truncated CAX1 failed to inhibit CAX1 activity. Both the CAX3 and VCAX1 regulatory regions could only inhibit CAX1 following mutagenesis of amino acids within these regions. These findings demonstrate that N-terminal regulation appears ubiquitous among plant CAX transporters, and suggest differential regulation among these transporters.