Mutations in Iron-Sulfur Cluster Scaffold Genes NFU1 and BOLA3 Cause a Fatal Deficiency of Multiple Respiratory Chain and 2-Oxoacid Dehydrogenase Enzymes

Abstract

Severe combined deficiency of the 2-oxoacid dehydrogenases, associated with a defect in lipoate synthesis and accompanied by defects in complexes I, II, and III of the mitochondrial respiratory chain, is a rare autosomal recessive syndrome with no obvious causative gene defect. A candidate locus for this syndrome was mapped to chromosomal region 2p14 by microcell-mediated chromosome transfer in two unrelated families. Unexpectedly, analysis of genes in this area identified mutations in two different genes, both of which are involved in [Fe-S] cluster biogenesis. A homozygous missense mutation, c.545G>A, near the splice donor of exon 6 in NFU1 predicting a p.Arg182Gln substitution was found in one of the families. The mutation results in abnormal mRNA splicing of exon 6, and no mature protein could be detected in fibroblast mitochondria. A single base-pair duplication c.123dupA was identified in BOLA3 in the second family, causing a frame shift that produces a premature stop codon (p.Glu42Argfs(∗)13). Transduction of fibroblast lines with retroviral vectors expressing the mitochondrial, but not the cytosolic isoform of NFU1 and with isoform 1, but not isoform 2 of BOLA3 restored both respiratory chain function and oxoacid dehydrogenase complexes. NFU1 was previously proposed to be an alternative scaffold to ISCU for the biogenesis of [Fe-S] centers in mitochondria, and the function of BOLA3 was previously unknown. Our results demonstrate that both play essential roles in the production of [Fe-S] centers for the normal maturation of lipoate-containing 2-oxoacid dehydrogenases, and for the assembly of the respiratory chain complexes.

Deleterious mutation in FDX1L gene is associated with a novel mitochondrial muscle myopathy

“…At least three instances of autosomal recessive disruption in genes playing an essential role in Fe-S biogenesis result in human phenotype accompanied by characteristic defects in complexes I, II and III of the mitochondrial respiratory chain. 14,15 In agreement with this, targeted disruption of fdx2 and NFU1, another late-acting maturation factor for a subset of mitochondrial Fe-S proteins, resulted in severely decreased content and activity of mitochondrial complex II (SDH) and the mitochondrial and cytosolic aconitases (only in fdx2 depletion) as well as impairment of lipoic acid containing enzymatic complexes. 16,17 Indeed, we also detected similar deficiencies in our Fdx2-deficient patient indicating that both SDH functional (enzyme activity) and content (immunoblotting) are affected (Figure 2).…”

Structural and Spectroscopic Insights into BolA-Glutaredoxin Complexes

“…The function of these holo-heterodimers is still not clear (6,9,50,51). The only characterized physiological role for a GrxBolA holo-heterodimer is in sensing the intracellular iron/Fe-S cluster status in yeast.…”

Iron–sulfur cluster biogenesis and trafficking in mitochondria

“…(Fig. 2) (12,13,(85)(86)(87)(88). Recent in vivo evidence indicates that the mitochondrial protein Nfu1 can interact with the [4Fe-4S] cluster machinery and with potential [4Fe-4S] target proteins, thus supporting its targeting function (89).…”

“…Two recent in vivo studies in yeast and a BOLA3 patient analysis suggested that Bol3 and Bol1 are involved in the maturation of a sub-class of mitochondrial [4Fe-4S] proteins, especially succinate dehydrogenase and lipoic acid synthase with its two [4Fe-4S] clusters, whereas several [2Fe-2S] proteins were assembled independently of the Bol proteins (Fig. 2) (13,89,93). Like Nfu1, the mitochondrial Bol proteins are not essential for viability of S. cerevisiae, and residual maturation of their target proteins was observed even in BOL double null mutants.…”