Mitochondrial calcium (Ca2+) uptake is central to many fundamental physiological processes. It stimulates ATP production during times of increased metabolic need and provides a Ca2+ sink to modulate Ca2+-mediated signaling locally within a cell. Mitochondrial Ca2+ concentrations also regulate apoptosis and dysregulation?? specifically, Ca2+ overload??is a hallmark of pathologies ranging from neuronal excitotoxicity to heart failure and some epilepsies to muscular dystrophies. Yet despite the importance of mitochondrial Ca2+ uptake in normal physiology and disease, the molecular machinery mediating this process is relatively recently identified and many fundamental questions remain to be answered. The main route of Ca2+ influx to mitochondria is a channel called mitochondrial calcium uniporter, which includes the ubiquitous pore-forming subunit MCU and, depending on the species, several regulatory subunits (termed ?uniplex? when in complex). This novel channel is highly selective for Ca2+, and its activity is tightly regulated by cytosolic Ca2+ concentration. My group recently determined a high-resolution crystal structure for a fungal MCU that defined a novel channel architecture and revealed a high-affinity Ca2+-binding site. Moreover, our cryo-EM structure of the human uniplex holocomplex revealed its architecture and hints at the mechanisms by which it is regulated. With these structures and the methods we developed, my lab is uniquely poised to embark on the mechanistic understanding of the mitochondrial calcium uniporter. Here, we propose to: 1) elucidate the structural and biophysical basis of ion selectivity, conduction and inhibition; 2) understand mechanisms of the channel gating and the long-range modulation; and 3) probe the molecular basis of Ca2+-dependent regulation of the uniplex. These results will give us much needed mechanistic insights into the activity and regulation of mitochondrial calcium uniporter, expanding our understanding of general principles of Ca2+ channels. In addition, they should provide a strong framework to aid the design of MCU inhibitors, which may represent promising treatments for diseases and pathologies marked by MCU dysregulation and mitochondrial Ca2+ overload. !

Public Health Relevance

The concentration of Ca2+ in mitochondria is tightly regulated under normal physiology and perturbed in many disease states, yet the primary channel that uptakes Ca2+ into mitochondria is not well understood. Here, we propose orthogonal studies to investigate the mechanisms that underlie the channel?s ion selectivity, gating and regulation. These experiments will reveal the molecular details of this important channel and, hopefully, help us design targeted modulators for use as therapeutics in the future.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Biophysics of Neural Systems Study Section (BPNS)
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Nie, Zhongzhen
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Stanford University
Schools of Medicine
United States
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