Yeast homologs of human MCUR1 regulate mitochondrial proline metabolism

Mohammad Zulkifli,Prachi P Trivedi,Jeramie D Watrous,John K Neff,Yingqi Chen,Natalie M Garza,Mohit Jain,Shrishiv A Timbalia,Marta Murgia,Steven K Anderson,Roland Nilsson,Muniswamy Madesh,Dhanendra Tomar,Vishal M Gohil

doi:10.1038/s41467-020-18704-1

Abstract

Mitochondria house evolutionarily conserved pathways of carbon and nitrogen metabolism that drive cellular energy production. Mitochondrial bioenergetics is regulated by calcium uptake through the mitochondrial calcium uniporter (MCU), a multi-protein complex whose assembly in the inner mitochondrial membrane is facilitated by the scaffold factor MCUR1. Intriguingly, many fungi that lack MCU contain MCUR1 homologs, suggesting alternate functions. Herein, we characterize Saccharomyces cerevisiae homologs Put6 and Put7 of MCUR1 as regulators of mitochondrial proline metabolism. Put6 and Put7 are tethered to the inner mitochondrial membrane in a large hetero-oligomeric complex, whose abundance is regulated by proline. Loss of this complex perturbs mitochondrial proline homeostasis and cellular redox balance. Yeast cells lacking either Put6 or Put7 exhibit a pronounced defect in proline utilization, which can be corrected by the heterologous expression of human MCUR1. Our work uncovers an unexpected role of MCUR1 homologs in mitochondrial proline metabolism.

Highlights

Mitochondria house evolutionarily conserved pathways of carbon and nitrogen metabolism that drive cellular energy production
We have focused on deciphering the functions of uncharacterized mitochondrial proteins that are evolutionarily conserved and most likely to be involved in the fundamental mitochondrial processes of energy generation and intermediary metabolism
We demonstrate that Put[6] and Put[7] are orthologues of human mitochondrial calcium uniporter regulator 1 (MCUR1) and are mitochondrial matrixfacing integral membrane proteins that form a large heterooligomeric complex required for proline utilization

Summary

Introduction

Mitochondria house evolutionarily conserved pathways of carbon and nitrogen metabolism that drive cellular energy production. The importance of mitochondria in fundamental cellular functions and human health has motivated systematic studies to define the mitochondrial proteome[5,6,7,8] Despite these advances, functional annotation of many of the evolutionarily conserved proteins lags behind. This limits our understanding of basic mitochondrial biology and the molecular basis of many human diseases emanating from mitochondrial dysfunction[9] To address this challenge, we have focused on deciphering the functions of uncharacterized mitochondrial proteins that are evolutionarily conserved and most likely to be involved in the fundamental mitochondrial processes of energy generation and intermediary metabolism. MCUR1 has been shown to physically interact with the mitochondrial Ca2+ uniporter (MCU), where it functions as a scaffold factor for hetero-oligomeric MCU complex assembly[10,11] These studies suggested a role of MCUR1 in regulating mitochondrial bioenergetics via MCU-mediated Ca2+ signaling. We demonstrate that Put[6] and Put[7] are orthologues of human MCUR1 and are mitochondrial matrixfacing integral membrane proteins that form a large heterooligomeric complex required for proline utilization

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Results

Conclusion