Modulation of the bacterial CobB sirtuin deacylase activity by N-terminal acetylation.

In eukaryotic cells, the N-terminal amino moiety of many proteins is modified by N-acetyltransferases (NATs). This protein modification can alter the folding of the target protein; can affect binding interactions of the target protein with substrates, allosteric effectors, or other proteins; or can trigger protein degradation. In prokaryotes, only ribosomal proteins are known to be N-terminally acetylated, and the acetyltransferases responsible for this modification belong to the Rim family of proteins. Here, we report that, in Salmonella enterica, the sirtuin deacylase CobB long isoform (CobBL) is N-terminally acetylated by the YiaC protein of this bacterium. Results of in vitro acetylation assays showed that CobBL was acetylated by YiaC; liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to confirm these results. Results of in vitro and in vivo experiments showed that CobBL deacetylase activity was negatively affected when YiaC acetylated its N terminus. We report 1) modulation of a bacterial sirtuin deacylase activity by acetylation, 2) that the Gcn5-related YiaC protein is the acetyltransferase that modifies CobBL, and 3) that YiaC is an NAT. Based on our data, we propose the name of NatA (N-acyltransferase A) in lieu of YiaC to reflect the function of the enzyme.

Sirtuin-Dependent Reversible Lysine Acetylation Controls the Activity of Acetyl Coenzyme A Synthetase in Campylobacter jejuni.

Posttranslational modifications are mechanisms for rapid control of protein function used by cells from all domains of life. Acetylation of the epsilon amino group (Nε) of an active-site lysine of the AMP-forming acetyl coenzyme A (acetyl-CoA) synthetase (Acs) enzyme is the paradigm for the posttranslational control of the activity of metabolic enzymes. In bacteria, this active-site lysine of Acs enzymes can be modified by a number of different GCN5-type N-acetyltransferases (GNATs). Acs activity is lost as a result of acetylation and is restored by deacetylation. Using a heterologous host, we show that Campylobacter jejuni NCTC11168 synthesizes enzymes that control Acs function by reversible lysine acetylation (RLA). This work validates the function of gene products encoded by the cj1537c, cj1715, and cj1050c loci, namely, the AMP-forming acetate-CoA ligase (CjAcs), a type IV GCN5-type lysine acetyltransferase (GNAT [CjLatA]), and a NAD+-dependent (class III) sirtuin deacylase (CjCobB), respectively. To our knowledge, these are the first in vivo and in vitro data on C. jejuni enzymes that control the activity of CjAcs. IMPORTANCE This work provides the experimental evidence needed to support the assignment of function to three key enzymes, two of which control the reversible posttranslational modification of an active-site lysyl residue of the central metabolic enzyme acetyl-CoA synthetase (CjAcs). We can now generate Campylobacter jejuni mutant strains defective in these functions, so we can establish the conditions in which this mode of regulation of CjAcs is triggered in this bacterium. Such knowledge may provide new therapeutic strategies for the control of this pathogen.