Cysteine variants in PMM2 lead to protein instability and higher sensitivity to oxidative stress in PMM2-CDG.

PMM2-congenital disorder of glycosylation (PMM2-CDG) is caused by genetic defects in PMM2, the gene encoding phosphomannomutase 2. Effective therapies for this disorder remain elusive. Recent studies emphasize cysteine's vulnerability to oxidative modifications that can instigate disease by facilitating inter-protein disulfide bonding, reducing protein mobility, highlighting its potential as a target for therapeutic intervention. Specifically, five cysteine-related pathogenic mutants have been identified in PMM2-CDG, namely Phe11Cys (F11C), Tyr64Cys (Y64C), Tyr76Cys (Y76C), Tyr106Cys (Y106C) and Gly228Cys (G228C), however the fundamental molecular mechanisms are still not fully understood. In this study, compared to wild-type (WT), Cys pathogenic mutants induced structural destruction, augmented hydrophobic exposure, reduced thermal stability, and a propensity to aggregate at physiological temperatures. Meanwhile, Cys mutants were sensitive to oxidative stress, which in the evident formation of aggregation. Molecular dynamics simulation revealed alterations in the core region and subunit binding free energy of homologous PMM2, instigated by the pathophysiogenic variants. Based on previous articles, we found cysteine pathogenic mutants can be partly rescued by celastrol. In summary, our findings provide critical insights into the molecular and functional impacts of specific cysteine variants in the PMM2 enzyme, offering a foundation for exploring novel therapeutic strategies for the prevention and treatment of PMM2-CDG.