Submitted to: Journal of Biological Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/12/2002
Publication Date: 2/21/2003
Citation: SHIGAKI,T., PITTMAN,J.K., HIRSCHI,K. ., MANGANESE SPECIFICITY DETERMINANTS IN THE ARABIDOPSIS METAL/H+ ANTIPORTER CAX2, JOURNAL OF BIOLOGICAL CHEMISTRY, 2003. v. 278. p. 6610-6617. Interpretive Summary: Nutrients such as manganese are needed in trace amounts for optimal growth of plants and humans, but manganese can be toxic if large amounts get into the cell. Both plants and animals regulate manganese levels by modifying the movement of this substance using various transporters. In this paper, we have identified and characterized a novel manganese transporter. As part of this characterization, we have identified the mechanism of manganese transport. Potentially, this transporter can be manipulated to manipulate manganese levels in edible portions of foods.
Technical Abstract: In plants and fungi, vacuolar transporters are thought to help remove potentially toxic cations from the cytosol. Metal/H+ antiporters are involved in metal sequestration into the vacuole; however, the specific transport properties and the ability to manipulate these transporters to alter substrate specificity is poorly understood. The Arabidopsis thaliana cation exchangers, CAX1 and CAX2 both appear to be able to transport calcium (Ca2+) into the yeast vacuole. There are 12 CAX-like transporters in Arabidopsis; however, as we demonstrate here, CAX2 was the only characterized CAX transporter capable of manganese (Mn2+) transport in yeast. In order to determine the domains within CAX2 which mediate Mn2+ specificity, six CAX2 mutants were constructed which contained different regions of the CAX1 transporter. One class displayed no alterations in Mn2+ or Ca2+ transport (3n), the second class showed a reduction in Ca2+ transport and no measurable Mn2+ transport (2n) and the third mutant, which contained 6 amino acids from CAX1 (CAX2-C), showed no reduction in Ca2+ transport and complete loss of Mn2+ transport. (FURTHER DETAILS PENDING). This study identified at least some of the residues important for metal selection and transport in a metal/H+ antiporter, an important family of transporters found in a variety of organisms.