The mechanism of MICU-dependent gating of the mitochondrial Ca2+uniporter.

Vivek Garg,Liron Boyman,Junji Suzuki,Yuriy Kirichok,Ishan Paranjpe,W Jonathan Lederer,Lorin S Milescu,Tiffany Unsulangi

doi:10.7554/elife.69312

Abstract

Ca2+ entry into mitochondria is through the mitochondrial calcium uniporter complex (MCUcx), a Ca2+-selective channel composed of five subunit types. Two MCUcx subunits (MCU and EMRE) span the inner mitochondrial membrane, while three Ca2+-regulatory subunits (MICU1, MICU2, and MICU3) reside in the intermembrane space. Here, we provide rigorous analysis of Ca2+ and Na+ fluxes via MCUcx in intact isolated mitochondria to understand the function of MICU subunits. We also perform direct patch clamp recordings of macroscopic and single MCUcx currents to gain further mechanistic insights. This comprehensive analysis shows that the MCUcx pore, composed of the EMRE and MCU subunits, is not occluded nor plugged by MICUs during the absence or presence of extramitochondrial Ca2+ as has been widely reported. Instead, MICUs potentiate activity of MCUcx as extramitochondrial Ca2+ is elevated. MICUs achieve this by modifying the gating properties of MCUcx allowing it to spend more time in the open state.

Highlights

Mitochondrial Ca2+ uptake regulates ATP production by modulating the activities of several dehydrogenases in the mitochondrial matrix primarily the pyruvate dehydrogenase and likely other control systems (Glancy and Balaban, 2012; McCormack et al, 1990; McCormack and Denton, 1993; Wescott et al, 2019)
The mitochondrial Ca2+ uniporter holocomplex (MCUcx) is composed of five distinct subunits types, two of which span the inner mitochondrial membrane (IMM) - MCU and EMRE - and two of the three MICU subunits (MICU1, MICU2, and MICU3) which reside in the intermembrane space (Baughman et al, 2011; De Stefani et al, 2011; Sancak et al, 2013)
This potentiation would result in efficient stimulation of the mitochondrial ATP production in response to cytosolic Ca2+ signaling events, when energy demand is increased as shown in neurons (Ashrafi et al, 2020) and heart (Wescott et al, 2019)

Summary

Introduction

Mitochondrial Ca2+ uptake regulates ATP production by modulating the activities of several dehydrogenases in the mitochondrial matrix primarily the pyruvate dehydrogenase and likely other control systems (Glancy and Balaban, 2012; McCormack et al, 1990; McCormack and Denton, 1993; Wescott et al, 2019). The MCUcx is composed of five distinct subunits types, two of which span the inner mitochondrial membrane (IMM) - MCU and EMRE - and two of the three MICU subunits (MICU1, MICU2, and MICU3) which reside in the intermembrane space (Baughman et al, 2011; De Stefani et al, 2011; Sancak et al, 2013). Recent structural discoveries (Wang et al, 2019; Fan et al, 2020; Wang et al, 2020b; Zhuo et al, 2021) suggest that the functioning channel is a dimer composed of two MCU/EMRE pores joined through the N-terminal of MCU subunits in the matrix, and MICU subunits in the intermembrane space.

Methods

Results

Conclusion