ABSORPTION AND METABOLISM OF ESSENTIAL MINERAL NUTRIENTS IN CHILDREN
Location: Children Nutrition Research Center (Houston, Tx)
Title: Characterization of zinc transport by divalent metal transporters of the ZIP family from the model legume medicago truncatula
Submitted to: Biometals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2010
Publication Date: February 1, 2011
Citation: Stephens, B.W., Cook, D.R., Grusak, M.A. 2011. Characterization of zinc transport by divalent metal transporters of the ZIP family from the model legume medicago truncatula. Biometals. 24(1):51-58.
Interpretive Summary: We are interested in understanding how legume crops, like pea, bean, and soybean, control their absorption and utilization of zinc, an essential micronutrient metal. We know that various proteins, located in cell membranes, are responsible for moving zinc into cells and into different cellular compartments. In this work, we characterized the transport attributes of several zinc transporting proteins. Specifically, these proteins came from the model legume, Medicago truncatula. Our results showed that Medicago truncatula has zinc transporters with a range of sensitivities and that these transporters may function in different compartments within the plant. The results also suggest that various crop legumes have a range of zinc transporters to assist with their zinc absorption and utilization.
To understand how plants from the Fabaceae family maintain zinc (Zn) homeostasis, we have characterized the kinetics of the Zn transporting proteins from the ZIP family of divalent metal transporters in the model legume Medicago truncatula. MtZIP1, MtZIP5, and MtZIP6 were the only members from this family determined to transport Zn and were further characterized. MtZIP1 has a low affinity for Zn with a Km of 1 uM, as compared to MtZIP5 and MtZIP6, that have a higher affinity for Zn with Km of 0.4 uM and 0.3 uM, respectively. Zn transport by MtZIP1 was more sensitive to inhibition by copper (Cu) concentrations than MtZIP5 and MtZIP6, because 3 uM Cu inhibited Zn transport by 80% in MtZIP1 while 5 uM Cu was required to achieve the same inhibition of Zn transport in MtZIP5 and MtZIP6. Cadmium (Cd) had a greater effect on the ability of MtZIP1 to transport Zn than MtZIP5 and MtZIP6, because at a concentration of 3 uM Cd, the Zn transport by MtZIP1 was inhibited 55% and the transport of Zn by MtZIP5 and MtZIP6 was inhibited by 20% to 30%. However, only MtZIP6 transported Cd at higher rates than those observed in the control plasmid pFL61, demonstrating a low affinity for Cd based on a Km of 57 uM. These results suggest that Medicago truncatula has both high and low affinity Zn transporters to maintain Zn homeostasis and that these transporters may function in different compartments within the plant.