Acetylation and Phosphorylation Regulate the Role of Pyruvate Kinase as a Glycolytic Enzyme or a Protein Kinase in Lamb

Protein post-translational modifications (PTMs) play an essential role in meat quality development. However, the effect of specific PTM sites on meat proteins has not been investigated yet. The characteristics of pyruvate kinase M (PKM) were found to exhibit a close correlation with final meat quality, and thus, serine 99 (S99) and lysine 137 (K137) in PKM were mutated to study their effect on PKM function. The structural and functional properties of five lamb PKM variants, including wild-type PKM (wtPKM), PKM_S99D (S99 phosphorylation), PKM_S99A (PKM S99 dephosphorylation), PKM_K137Q (PKM K137 acetylation), and PKM_K137R (PKM K137 deacetylation), were evaluated. The results showed that the secondary structure, tertiary structure, and polymer formation were affected among different PKM variants. In addition, the glycolytic activity of PKM_K137Q was decreased because of its weakened binding with phosphoenolpyruvate. In the PKM_K137R variant, the actin phosphorylation level exhibited a decrease, suggesting a low kinase activity of PKM_K137R. The results of molecular simulation showed a 42% reduction in the interface area between PKM_K137R and actin, in contrast to wtPKM and actin. These findings are significant for revealing the mechanism of how PTMs regulate PKM function and provide a theoretical foundation for the development of precise meat quality preservation technology.