Zhiwu Zhu - US grants

DESCRIPTION (adapted from applicant's abstract): Human Menkes and Wilsons diseases are caused by homeostatic defects of a metal ion, copper (Cu2+ and Cu+). Copper ion is a dynamic biological nature, essential yet toxic. The two diseases represent the two extremes in copper ion homeostasis: copper ions deficiency and excess. Copper ion deficiency caused loss of function of copper ion-dependent enzymes leads to Menkes disease. Copper ion excess mediated toxicity is Wilson's disease. Since the copper ion is an essential nutrient yet a potent toxin, cells must possess a dynamic homeostasis to maintain a proper cellular level of copper ions. What is the molecular mechanism of dynamic copper ion homeostasis? This is still a fundamental question to be addressed. The goal of this proposal is, using yeast as a model system, to study the dynamic regulation in copper ion homeostasis. Yeast cells carry out similar biochemical reactions to those required in humans. Furthermore, copper ion homeostatic mechanisms are largely conserved among yeast, human and other divergent species. Mac1p, a putative metal ion sensing yeast protein, functions as a key regulatory factor in high affinity copper ion uptake and transport under physiological conditions. Recent studies have demonstrated that Mac1p responds to toxic levels of copper ions through an uncharacterized mechanism of regulated protein degradation. Mac1p degradation is a new mechanism in copper ion homeostasis and independent of its regulatory function in copper ion transporter gene CTR1 and CTR3 expression. The differential functions of Mac1p under physiological and toxic copper ion conditions reflect the dynamic biological nature of copper ions. Therefore, understanding Mac1p functions will be instrumental to determine molecular mechanism of dynamic copper ion homeostasis. In this proposal, a combination of genetic, molecular biology, chemical and biochemical methods are designed to determine the precise molecular mechanisms of Mac1p functions. These approaches will be applied to address the following questions: (1) how does Mac1p respond differentially to physiological and toxic levels of copper ions? (2) how does Mac1p sense copper ion and its concentration changes? (3) What is the molecular mechanism and importance of regulated protein degradation in copper ion homeostasis? The outcomes of these proposed research will make fundamental contributions to the understanding of dynamic copper ion homeostasis.

9807786
Zhu
Copper ion is essential yet toxic for all living organisms. Because of this dual nature, cells must posses a dynamic homeostasis to maintain a proper cellular level of copper ion: not too low to cause deficiency and not too high to cause toxicity. What is the molecular mechanism of dynamic copper ion homeostasis? This is still a fundamental question to be addressed. Therefore, it is absolutely critical to understand copper ion homeostatic mechanisms. The goal of this project is, using yeast as a model system, to study the dynamic regulation of copper ion homeostasis. Yeast cells carry out similar biochemical reactions to those required in humans, and copper ion homeostatic mechanisms are largely conserved among yeast, human and other divergent species. In yeast, copper ion uptake and transport under physiological conditions is regulated by a putative copper ion-sensing protein, Mac 1p. Recent studies have shown that Mac lp also responds to toxic levels of copper ions through an uncharacterized mechanism of regulated protein degradation. Mac lp degradation is a new mechanism in copper ion homeostasis. The differential functions of Mac lp under physiological and toxic copper ion conditions reflect the dynamic biological nature of copper ions. Therefore, understanding Mac lp functions will be instrumental in determining molecular mechanism of dynamic copper ion homeostasis. This project, using a combination of molecular biological, chemical and biochemical methods, will to determine the precise molecular mechanisms of Mac lp functions. These approaches will be applied to achieve two specific aims: (1) to further characterize how Mac lp responds differentially to physiological and toxic levels of copper ions, (2) to elucidate the biochemical mechanisms of Mac 1p sensing and differentiating physiological and toxic levels of copper ions. The outcomes of this research will make fundamental contributions to understanding of the molecular mechanism of dynamic copper ion homeostasis. The results will also provide critical insights into the fields of metal ions in biology and regulated protein degradation.

This project will study a fundamentally important question in biology, that is, how living organisms monitor and ensure an adequate supply of nutrients during organismal development. Nutrient deprivation is known to stop the cells from dividing. The cell cycle is the most basic process underlying organismal development. One essential nutrient is copper, which is somewhat unique in that it is essential but toxic at high levels. Thus, the cells have to keep a balanced copper level so that it is not too low and not too high. To balance the copper content, the cells must sense and signal the copper status of the environment in which they live and divide. Currently, very little is known about how cells monitor the copper availability so that they either increase or block taking up copper from the environment. This project uses the baker's yeast Saccharomyces cerevisiae to study how living organisms secure enough copper for growth and development. Preliminary studies observed in yeast show that copper taken in from the environment is under the control of processes that drive cell division. This discovery shows that the cell cycle and nutrient copper homeostasis are integrated with each other. Thus, the study of cell cycle controlling copper uptake will serve as a model for the understanding of how cells monitor and ensure an adequate supply of nutrients during cell development. The research will not only help to solve a fundamental question in cell biology but also mechanistically link the fields of cell cycle biology, nutrition sciences, and the biology of metal ions. They will expand the current understanding of the roles for the cell cycle in cell biology. This research also provides an excellent opportunity for training graduate and undergraduate students in a multidisciplinary research environment.