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.