Engineered bacterial lipoate protein ligase A (lplA) restores lipoylation in cell models of lipoylation deficiency.

Protein lipoylation, a vital lysine posttranslational modification (PTM), plays a crucial role in the function of key mitochondrial TCA cycle enzymatic complexes. In eukaryotes, lipoyl PTM synthesis occurs exclusively through de novo pathways, relying on lipoyl synthesis/transfer enzymes, dependent upon mitochondrial fatty acid and Fe-S cluster biosynthesis. Dysregulation in any of these pathways leads to diminished cellular lipoylation. Efficient restoration of lipoylation in lipoylation deficiency cell states using either chemical or genetic approaches has been challenging due to pathway complexity and multiple upstream regulators. To address this challenge, we explored the possibility that a bacterial lipoate protein ligase (lplA) enzyme, that can salvage free lipoic acid bypassing the dependency on de novo synthesis, could be engineered to be functional in human cells. Overexpression of the engineered lplA in lipoylation null cells restored lipoylation levels, cellular respiration, and growth in low glucose conditions. Engineered lplA restored lipoylation in all tested lipoylation null cell models, mimicking defects in mitochondrial fatty acid synthesis (MECR KO), Fe-S cluster biosynthesis (BOLA3 KO), and specific lipoylation regulating enzymes (FDX1, LIAS and LIPT1 KOs). Furthermore, we describe a patient with a homozygous c.212C>T variant LIPT1 with a previously uncharacterized syndromic congenital sideroblastic anemia. K562 erythroleukemia cells engineered to harbor this missense LIPT1 allele recapitulate the lipoylation deficient phenotype and exhibit impaired proliferation in low glucose that is completely restored by engineered lplA. This synthetic approach offers a potential therapeutic strategy for treating lipoylation disorders.