Mutations in LYRM4, encoding iron–sulfur cluster biogenesis factor ISD11, cause deficiency of multiple respiratory chain complexes

Abstract

Iron-sulfur clusters (ISCs) are important prosthetic groups that define the functions of many proteins. Proteins with ISCs (called iron-sulfur or Fe-S proteins) are present in mitochondria, the cytosol, the endoplasmic reticulum and the nucleus. They participate in various biological pathways including oxidative phosphorylation (OXPHOS), the citric acid cycle, iron homeostasis, heme biosynthesis and DNA repair. Here, we report a homozygous mutation in LYRM4 in two patients with combined OXPHOS deficiency. LYRM4 encodes the ISD11 protein, which forms a complex with, and stabilizes, the sulfur donor NFS1. The homozygous mutation (c.203G>T, p.R68L) was identified via massively parallel sequencing of >1000 mitochondrial genes (MitoExome sequencing) in a patient with deficiency of complexes I, II and III in muscle and liver. These three complexes contain ISCs. Sanger sequencing identified the same mutation in his similarly affected cousin, who had a more severe phenotype and died while a neonate. Complex IV was also deficient in her skeletal muscle. Several other Fe-S proteins were also affected in both patients, including the aconitases and ferrochelatase. Mutant ISD11 only partially complemented for an ISD11 deletion in yeast. Our in vitro studies showed that the l-cysteine desulfurase activity of NFS1 was barely present when co-expressed with mutant ISD11. Our findings are consistent with a defect in the early step of ISC assembly affecting a broad variety of Fe-S proteins. The differences in biochemical and clinical features between the two patients may relate to limited availability of cysteine in the newborn period and suggest a potential approach to therapy.

Mapping Key Residues of ISD11 Critical for NFS1-ISD11 Subcomplex Stability

“…Reinforcing the idea, the ISD11 ts mutants and COXPD19-associated disease variant (R68A/R68L) showed reduced mitochondrial membrane potential and diminished respiratory activity with lower ATP levels in the mitochondria. Based on these findings, it is reasonable to believe that reduced respiratory activity associated with the R68L ISD11 mutation in COXPD19 patients may be responsible for the manifestation of disease symptoms, especially the most common symptom of respiratory distress (23).…”

“…Required for Cell Growth and Survival-Human mitochondrial matrix protein ISD11 (Isd11 in yeast) assists the function of the sulfur donor protein NFS1 (Nfs1 in yeast) (22,23,31). Although there is no bacterial ortholog of the ISD11 protein, it is well conserved in eukaryotes, ranging from yeast to humans as highlighted in multiple sequence alignment (Fig.…”

“…Of these, the Arg-68 residue was identified to be critical for ISD11 function because an R68L conversion leads to development of combined oxidative phosphorylation deficiency (COXPD19) in humans ( Fig. 1C) (23). Interestingly, none of the 8 mutants of ISD11 could completely rescue the lethal phenotype of the ⌬isd11 strain on 5-FOA media.…”

“…Although Isd11 is not required for desulfurase activity of Nfs1 in vitro, the Nfs1-Isd11 complex represents the functional sulfur donor, in vivo (21). In humans, the Isd11 ortholog ISD11 is believed to play a similar conserved role in Fe-S cluster biogenesis (22) and loss of ISD11 function results in a mitochondrial disorder termed as combined oxidative phosphorylation deficiency 19 (COXPD19) 5 (23). Recent studies on human ISD11 have shown that a homozygous mutation in the LYRM4 gene on chromosome 6p25, which codes for the ISD11 protein, converts a conserved arginine residue at position 68 into leucine (R68L) implicated in the mitochondrial genetic disorder COXPD19.…”

Du fer et du soufre dans les protéines

“…révélé chez les deux patients une mutation dans le gène ISD11/LYRM4 (LYR motif containing 4) [9,46]. Cette mutation provoque la substitution d'un résidu arginine conservé en leucine.…”