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N-terminal (Nt)-acylation is the irreversible addition of an acyl moiety to the terminal alpha amino group of a peptide chain. This type of modification alters the nature of the N terminus, which can interfere with the function of the modified protein by disrupting protein interactions, function, localization, degradation, hydrophobicity, or charge. Nt acylation is found in all domains of life and is a highly common occurrence in eukaryotic cells. However, in prokaryotes very few cases of Nt acylation have been reported. It was once thought that Nt acylation of proteins, other than ribosomal proteins, was uncommon in prokaryotes, but recent evidence suggests that this modification may be more common than once realized. In this review, we discuss what is known about prokaryotic Nt acetylation and the acetyltransferases that are responsible, as well as recent advancements in this field and currently used methods to study Nt acetylation.

Several of the enzymes involved in the conversion of adenosylcobyric acid (AdoCby) to adenosylcobamide (AdoCba) are yet to be identified and characterized in some cobamide (Cba)-producing prokaryotes. Using a bioinformatics approach, we identified the bluE gene (locus tag RSP_0788) of Rhodobacter sphaeroides 2.4.1 as a putative functional homologue of the L-threonine kinase enzyme (PduX, EC 2.7.1.177) of S. enterica. In AdoCba, (R)-1-aminopropan-2-ol O-phosphate (AP-P) links the nucleotide loop to the corrin ring; most known AdoCba producers derive AP-P from L-Thr-O-3-phosphate (L-Thr-P). Here, we show that RsBluE has L-Thr independent ATPase activity in vivo and in vitro. We used (31)P-NMR spectroscopy to show that RsBluE generates L-Thr-P at the expense of ATP and is unable to use L-Ser as substrate. BluE from R. sphaeroides or Rhodobacter capsulatus restored AdoCba biosynthesis in S. enterica ΔpduX and R. sphaeroides ΔbluE mutant strains. R. sphaeroides ΔbluE strains exhibited a decreased pigment phenotype that was restored by complementation with BluE. Finally, phylogenetic analyses revealed that bluE was restricted to the genomes of a few Rhodobacterales that appear to have a preference for a specific form of Cba, namely Coα-(α−5,6-dimethylbenzimidazolyl-Coβ-adenosylcobamide (a.k.a. adenosylcobalamin, AdoCbl; coenzyme B(12), CoB(12)).

The extensive involvement of the reversible lysine acylation (RLA) system in metabolism has attracted the attention of investigators interested in understanding the fundamentals of prokaryotic and eukaryotic cell function. Research in this area of cell physiology is diverse, ranging, among others, from probing the molecular bases of human diseases, to optimizing engineered metabolic pathways for biotechnological applications, to advancing our understanding of fundamental cellular processes. A gap of knowledge exists in our understanding of the regulatory circuitry that integrates the expression of genes encoding modifiers (i.e., acyltransferases) and demodifiers (i.e., deacylases) with the expression of genes encoding known targets of the system. Here we discuss the implications of recently reported work performed in the enteropathogen Salmonella enterica (mBio (2015) 6(4):e00891-15), which provided the first insights into the integration of the transcriptional regulation of genes encoding the RLA system with the acs gene encoding the central metabolic enzyme acetyl-CoA synthetase (Acs).

Salmonella enterica catabolizes ethanolamine inside a compartment known as the metabolosome. The ethanolamine utilization (eut) operon of this bacterium encodes all functions needed for the assembly and function of this structure. To date, the roles of the EutQ and EutP were not known. Herein we show that both proteins have acetate kinase activity, and that EutQ is required during anoxic growth of S. enterica on ethanolamine and tetrathionate. EutP and EutQ-dependent ATP synthesis occurred when enzymes were incubated with ADP, Mg(II) ions and acetyl-phosphate. EutQ and EutP also synthesized acetyl-phosphate from ATP and acetate. Although EutP had acetate kinase activity, ΔeutP strains lacked discernable phenotypes under the conditions where ΔeutQ strains displayed clear phenotypes. The kinetic parameters indicate that EutP is a faster enzyme than EutQ. Our evidence supports the conclusions that EutQ and EutP represent novel classes of acetate kinases. We propose that EutQ is necessary to drive flux through the pathway under physiological conditions, preventing a buildup of acetaldehyde. We also suggest that ATP generated by these enzymes may be used as a substrate for EutT, the ATP-dependent corrinoid adenosyltransferase, and for the EutA ethanolamine ammonia-lyase reactivase.