Lactyllysine Esterification Enables Efficient Lactylprotein Expression via Genetic Code Expansion and Supports Functional Proteomics Studies.

Lysine lactylation has recently been discovered and demonstrated to be an essential player in immunity, cancer and neurodegenerative diseases. Genetic code expansion (GCE) technique is powerful in uncovering lactylation functions, since it allows site-specific incorporation of lactyllysine (Klac) into proteins of interest (POIs) in living cells. However, the inefficient uptake of Klac into cells, due to its high hydrophilicity, results in limited expression of lactylated POIs. To address this challenge, here we designed esterified Klac derivatives, exemplified by ethylated Klac (KlacOEt), to enhance Klac's lipophilicity and improve its cellular uptake. The expression level of site-specifically lactylated POIs was doubled using KlacOEt in both and HEK293T cells. Immunoprecipitation mass spectrometry analysis verified the significantly increased yield of the precisely lactylated fructose-bisphosphate aldolase A using KlacOEt. Furthermore, in conjunction with the Target Responsive Accessibility Profiling approach, we found that lactylation at ALDOA-K147 altered the protein's conformation, which may explain the lactylation-induced reduction in enzyme activity. Together, we demonstrate that, through enhancing the yield of lactylated proteins with Klac esters via GCE, we are able to site-specifically reveal the effects of lactylation on POIs' interactions, conformations and activities using a suite of functional proteomics and biochemical tools.