Submitted to: Molecular Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/30/2004
Publication Date: 11/1/2004
Citation: Pittman, J.K., Cheng, N., Shigaki, T., Kunta, M., Hirschi, K. 2004. Functional dependence on calcineurin by variants of the saccharomyces cerevisiae vacuolar ca2+/h+ exchanger vcx1p. Molecular Microbiology. 54(4):1104-1116. Interpretive Summary: Understanding how plants and animals adapt to change is an important component of basic biology. In order to keep this simple and fast, the brewer's yeast is sometimes used as a model system because many of the basic components of biology are found in this laboratory fungus. In this study, we have used yeast to understand how organisms adapt to alterations in the growth media. We have elucidated how a specific regulator can modulate a given target in many different ways. Insights from this work will aid in our ability to eventually modulate plants and animals to improve human health.
Technical Abstract: The Ca(2+)-dependent protein phosphatase calcineurin is an important regulator of ion transporters from many organisms, including the Saccharomyces cerevisiae vacuolar Ca(2+)/H(+) exchanger Vcx1p. In yeast and plants, cation/H(+) exchangers are important in shaping cytosolic Ca(2+) levels involved in signal transduction and providing tolerance to potentially toxic concentrations of cations such as Ca(2+), Mn(2+) and Cd(2+). Previous genetic evidence suggested Vcx1p is negatively regulated by calcineurin. By utilizing direct transport measurements into vacuolar membrane vesicles, we demonstrate that Vcx1p is a low-affinity Ca(2+) transporter and may also function in Cd(2+) transport, but cannot transport Mn(2+). Furthermore, direct Ca(2+) transport by Vcx1p is calcineurin sensitive. Using a yeast growth assay, a mutant allele of VCX1 (VCX1-S204A/L208P), termed VCX1-M1, was previously found to confer strong Mn(2+) tolerance. Here we demonstrate that this Mn(2+) tolerance is independent of the Ca(2+)/Mn(2+)-ATPase Pmr1p and results from Mn(2+)-specific vacuolar transport activity of Vcx1-M1p. This Mn(2+) transport by Vcx1-M1p is calcineurin dependent, although the localization of Vcx1-M1p to the vacuole appears to be calcineurin independent. Additionally, we demonstrate that mutation of L208P alone is enough to confer calcineurin-dependent Mn(2+) tolerance. This study demonstrates that calcineurin can positively regulate the transport of cations by VCX1-M1p