Crosstalk Between Lysine Lactylation and Acetylation Regulates Lactate Dehydrogenase in <i>Streptococcus mutans</i>

Post-translational modifications (PTMs) provide essential fine-tuning of protein functions in response to environmental changes. Among the PTMs, lysine acetylation (Kac) and the recently identified lysine lactylation (Kla) play crucial roles in metabolic regulation considering that lactate and acetyl-CoA (Ac-CoA) are generated from pyruvate as the outlet of glycolysis. However, their crosstalk and regulatory mechanisms remain largely unknown, particularly in prokaryotes. Herein, we investigated the intricate interrelation between Kla and Kac in the cariogenic bacterium Streptococcus mutans, a prolific producer of lactate. We conducted a comprehensive profiling of Kla and Kac, observing their wide distribution in glycolytic enzymes. Lactate dehydrogenase (LDH), the terminal enzyme of glycolysis, exhibited dynamic Kla and Kac shifts in line with glycolytic intermediates, where the ratio of Kla to Kac denotes the metabolic influx. Furthermore, ActA was pinpointed as a dual-function acyltransferase catalyzing the Kla and Kac of LDH, both negatively regulating its enzymatic activity. Importantly, the study identifies lysine 307 (K307) on LDH as a critical site, with its acylation significantly altering LDH activity, thereby lactate production and bacterial growth. Our insights into the metabolic regulation mediated by Kla and Kac contribute to the understanding of the metabolism-PTM-metabolism feedback loop, allowing bacteria to fine-tune their metabolism based on the availability of metabolic intermediates.