NDUFS3 depletion permits complex I maturation and reveals TMEM126A/OPA7 as an assembly factor binding the ND4-module intermediate.

Luigi D’Angelo,Monica De Luise,Anna Maria Porcelli,Massimo Zeviani,Elisa Astro,Shujing Ding,Nikkitha Umesh-Ganesh,Giuseppe Gasparre,Ivana Kurelac,Luisa Iommarini,Ian M Fearnley,Erika Fernandez-Vizarra

doi:10.1016/j.celrep.2021.109002

Abstract

SummaryComplex I (CI) is the largest enzyme of the mitochondrial respiratory chain, and its defects are the main cause of mitochondrial disease. To understand the mechanisms regulating the extremely intricate biogenesis of this fundamental bioenergetic machine, we analyze the structural and functional consequences of the ablation of NDUFS3, a non-catalytic core subunit. We show that, in diverse mammalian cell types, a small amount of functional CI can still be detected in the complete absence of NDUFS3. In addition, we determine the dynamics of CI disassembly when the amount of NDUFS3 is gradually decreased. The process of degradation of the complex occurs in a hierarchical and modular fashion in which the ND4 module remains stable and bound to TMEM126A. We, thus, uncover the function of TMEM126A, the product of a disease gene causing recessive optic atrophy as a factor necessary for the correct assembly and function of CI.

Highlights

Human complex I (CI; NADH:ubiquinone oxidoreductase), the largest multi-heteromeric enzyme of the mitochondrial respiratory chain (MRC), is composed of 45 subunits encoded by both the nuclear DNA and mitochondrial DNA (Hirst, 2013; Sazanov, 2015)
A residual, fully assembled, and functional respiratory CI is present upon NDUFS3 ablation We have previously reported that the genetic ablation of NDUFS3 in two human cell lines, from osteosarcoma 143BÀ/À and colorectal carcinoma HCT116À/À, induced a severe decrease of both CI NADH dehydrogenase activity and CI-driven ATP production (Kurelac et al, 2019)
Such residual CI activity was evident in the two NDUFS3null cell models by CI in-gel activity (CI-IGA) in both isolated, fully assembled CI and in SCs (Figures 1B, 1C, S1C, and S1D)

Summary

Introduction

Human complex I (CI; NADH:ubiquinone oxidoreductase), the largest multi-heteromeric enzyme of the mitochondrial respiratory chain (MRC), is composed of 45 subunits encoded by both the nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) (Hirst, 2013; Sazanov, 2015). Supernumerary subunits are all nDNA encoded, whereas seven core subunits (MTND1–6 and MT-ND4L) are encoded by mtDNA (Vinothkumar et al, 2014; Zhu et al, 2016) This gigantic complex has a distinctive L-shaped structure with a hydrophilic arm protruding into the matrix and a hydrophobic arm embedded in the inner mitochondrial membrane. The transmembrane P-module contains all the mtDNA-encoded subunits and can be further divided into two proximal modules (the ND1- and ND2-modules) plus two distal modules (the ND4- and ND5-modules) (GuerreroCastillo et al, 2017; Sanchez-Caballero et al, 2016a; Stroud et al, 2016) Such modular organization reflects the enzyme evolution (Friedrich and Scheide, 2000; Moparthi and Hagerhall, 2011), structure (Agip et al, 2018) and function (Hirst, 2013), as well as the pathways involved in its assembly (Guerrero-Castillo et al, 2017). CI biogenesis is an intricate process that takes place in a modular fashion, in which each of the functional submodules are assembled and stabilized by a number of specific

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Discussion

Conclusion