4.1.1. Regulation of enzymatic activity
In prokaryotes, the role of N-lysine acetylation regulating enzymatic activity was first reported in the acetyl-CoA synthetase (Acs) ofS. enterica (Starai et al., 2002). In vivo and in vitro assays showed that Pat interacts with leucine 641 of Acs, leading to acetylation of lysine-609, decreasing Acs’s activity, the incubation of the acetylated enzyme with NAD+-dependent deacetylase CobB results in its activation. A Leu-641 Acs mutant showed that position 641 has a structural contribution that allows the interaction of Acs with the protein acetyltransferase (Pat) (Starai & Escalante-Semerena, 2004; Starai et al., 2002; Starai et al., 2004). In other bacteria (E. coli, B. subtilis, Saccharopolyspora erythraea, Rhodopseudomonas palustris, and M. smegmatis ) similar acetylation-dependent regulatory modes of Acs have been described (Castaño-Cerezo et al., 2015; Crosby et al., 2012; Gardner et al., 2006; Kim et al., 2013; Xu et al., 2011; You et al., 2014).
Interestingly, Mycobacterium tuberculosis employs acetylation instead of phosphorylation to regulate isocitrate dehydrogenase (ICDH). The enzyme is acetylated in two lysine residues by Rv2170, reducing the enzymatic activity to around 30% (Lee et al., 2017).
As demonstrated by Venkat et al. (2017), protein acetylation can also increase enzyme activity. The enzymatic activity of different acetylated variants of malate dehydrogenase (MDH) obtained by the expansion of the genetic code strategy showed that only the acetylation at positions K99 and K140 and the doubly acetylated MDH at both positions increased the enzyme activity. In other variants, no effect was observed. The authors also demonstrated that MDH acetylation can occur either enzymatically or non-enzymatically and that the level of MDH acetylation increases in a glucose-dependent manner (Venkat et a., 2017).
In other proteins, the effect on activity depends on the lysine residue that is acetylated. For example, the enzyme assay and kinetic analysis of different acetylated variants of E. coli citrate synthase (CS), showed that lysine acetylation could decrease the overall CS enzyme activity, mainly due to the acetylation of K295, which impaired the binding of acetyl-coenzyme A. However, acetylation at K283 increased the enzymatic activity since the binding of acetyl-coenzyme A is promoted (Venkat et al., 2019). The same result was observed in the isocitrate dehydrogenase (ICDH) (Venkat et al., 2018).
These studies prove that acetylation modulates the activity of central metabolic enzymes and eventually alters protein function for controlling competing pathways.