Role of Nfu1 and Bol3 in iron-sulfur cluster transfer to mitochondrial clients

Andrew Melber,Un Na,James A Wohlschlegel,Dennis R Winge,Ajay Vashisht,Benjamin D Weiler,Roland Lill

doi:10.7554/elife.15991

Abstract

Iron-sulfur (Fe-S) clusters are essential for many cellular processes, ranging from aerobic respiration, metabolite biosynthesis, ribosome assembly and DNA repair. Mutations in NFU1 and BOLA3 have been linked to genetic diseases with defects in mitochondrial Fe-S centers. Through genetic studies in yeast, we demonstrate that Nfu1 functions in a late step of [4Fe-4S] cluster biogenesis that is of heightened importance during oxidative metabolism. Proteomic studies revealed Nfu1 physical interacts with components of the ISA [4Fe-4S] assembly complex and client proteins that need [4Fe-4S] clusters to function. Additional studies focused on the mitochondrial BolA proteins, Bol1 and Bol3 (yeast homolog to human BOLA3), revealing that Bol1 functions earlier in Fe-S biogenesis with the monothiol glutaredoxin, Grx5, and Bol3 functions late with Nfu1. Given these observations, we propose that Nfu1, assisted by Bol3, functions to facilitate Fe-S transfer from the biosynthetic apparatus to the client proteins preventing oxidative damage to [4Fe-4S] clusters.

Highlights

It was previously reported that nfu1D cells exhibit specific but partial defects in the formation of [4Fe-4S] clusters analogous to phenotypes seen in patients with mitochondrial dysfunction syndrome (Navarro-Sastre et al, 2011; Schilke et al, 1999)
Biochemistry harboring mutations in NFU1, as well as BOLA3, exhibit biochemical abnormalities in a set of [4Fe4S] enzymes leading to speculation that Nfu1, and BolA3, function as a late from defective iron-sulfur (Fe-S) maturation factor (Navarro-Sastre et al, 2011; Py et al, 2012) or that Nfu1 is an alternate Fe-S cluster synthesis scaffold protein used for a subset of specific Fe-S client proteins (Cameron et al, 2011; Tong et al, 2003)
We demonstrate in studies using yeast as a model system that the yeast orthologs of human NFU1 and BOLA3 function in a late step of transfer of [4Fe-4S] clusters to specific client proteins

Summary

Introduction

A severe syndrome characterized by the dysfunction of multiple mitochondrial enzymes has been described for a series of patients with mutations in four mitochondrial proteins IBA57, ISCA2, NFU1 and BOLA3 (Seyda et al, 2001; Cameron et al, 2011; Navarro-Sastre et al, 2011; FerrerCortes et al, 2013; Nizon et al, 2014; Baker et al, 2014; Debray et al, 2015; Lossos et al, 2015; Al-Hassnan et al, 2015). The syndrome is associated with an impairment of lipoic acid-dependent 2-oxoacid dehydrogenases arising from defective lipoate synthesis and defects in respiratory complexes I and II in select tissues including muscle and liver. These phenotypes arise from defective iron-sulfur (Fe-S) cluster assembly within the mitochondria. Whereas IBA57 and ISCA2 are known components of the ISA complex, along with ISCA1, which functions in the formation of [4Fe-4S] clusters within mitochondria (Muhlenhoff et al, 2011; Gelling et al, 2008; Sheftel et al, 2012), the functions of NFU1 and BOLA3 in Fe-S cluster assembly remain an enigma

Methods

Results

Conclusion