Ectopic protein lysine methacrylation contributes to defects caused by loss of HIBCH or ECHS1.

The absence of HIBCH or ECHS1, two Leigh syndrome genes, in cultured cells results in abnormal mitochondrial morphology and respiratory defects. Fly eyes lacking either protein exhibit age-dependent degeneration. Elevated lysine methacrylation (Kmea) is observed in both HIBCH- and ECHS1-deficient cells and fly tissues. Quantitative mass spectrometry reveals that many proteins are ectopically modified by Kmea in these cells. Mimicking Kmea in proteins like CH60, FKBP4, BIP, LDHB, or DHRS2 replicates the mitochondrial morphology changes seen in HIBCH- or ECHS1-deficient cells. Reducing Kmea modification partially rescues mitochondrial morphology changes in cells and eye degeneration in flies. Fibroblasts from patients with HIBCH or ECHS1 mutations show similar mitochondrial changes and elevated Kmea, which are significantly reversed by administering N-acetyl-L-cysteine to reduce Kmea levels. We propose that ectopic Kmea modification mediates the defects caused by HIBCH- or ECHS1-deficiency. Reducing Kmea modification provides a new approach for treating HIBCH- or ECHS1-related Leigh syndrome.