N-terminal acetylation (Nt-acetylation) is a ubiquitous protein modification involving the transfer of an acetyl moiety from acetyl-CoA to the α-amino group of a nascent polypeptide. The modification is presumed irreversible and is catalyzed by a group of enzymes called N-terminal acetyltransferases (NATs). The NATs have defined substrate specificities, which are largely determined by the N-terminal sequence identity. The acetylation event can be partial or complete and occurs primarily cotranslational. The biological role of Nt-acetylation remains an enigma. Increasing evidence suggest that Nt-acetylation has diverse molecular functions depending upon the protein being targeted, such as protein degradation, protein folding, protein-protein interaction, and membrane targeting.
Another major type of protein acetylation is the more commonly known lysine acetylation. Unlike Nt-acetylation, lysine acetylation is a reversible process, due to the action of lysine deacetylases. An additional level of regulation is provided by the sensitivity towards the availability of acetyl-CoA. This is particularly the case for histone lysine acetylation where energy availability, and thus acetyl-CoA levels, is linked to altered expression of genes involved in metabolism.
Although the intricate linkage between lysine acetylation and metabolism has been highlighted by several studies, the effect of cellular energy status on Nt-acetylation remains unclear. To address this, we have used COFRADIC proteomics to perform a global analysis of Nt-acetylation in response to nutrient starvation. Our study shows that Nt-acetylation is largely unaffected by alterations in cellular metabolism. However, a minor group of cytosolic proteins are differentially acetylated at their N-termini. The majority of affected neo-N-termini presented the same acetylation trend as histones, becoming less acetylated at stationary phase. To our surprise, a group of affected mature N-termini were more acetylated in stationary phase as compared to active phase. Our results indicate that specific Nt-acetylation events are subjected to metabolic-dependent regulation. This is the first study concerning regulation of Nt-acetylation from a nutrient perspective, and thus provides an important insight to metabolic regulation of protein acetylation as an entirety.