Regulation of translation by lysine acetylation in Escherichia coli

Abstract

N{varepsilon}-lysine acetylation is a common post-translational modification observed in diverse species of bacteria. Aside from a few central metabolic enzymes and transcription factors, little is known about how this post-translational modification regulates protein activity. In this work, we investigated how lysine acetylation affects translation in Escherichia coli. In multiple species of bacteria, ribosomal proteins are highly acetylated at conserved lysine residues, suggesting that this modification may regulate translation. In support of this hypothesis, we found that the addition of the acetyl donors, acetyl phosphate or acetyl-Coenzyme A, inhibits translation but not transcription using an E. coli cell-free system. Further investigations using in vivo assays revealed that acetylation does not appear to alter the rate of translation elongation but rather increases the proportion of dissociated 30S and 50S ribosomes, based on polysome profiles of mutants or growth conditions known to promote lysine acetylation. Furthermore, ribosomal proteins are more acetylated in the disassociated 30S and 50S ribosomal subunit than in the fully assembled 70S complex. The effect of acetylation is also growth rate dependent, with disassociation of the subunits most pronounced during late exponential and early stationary phase growth - the same growth phase where protein acetylation is greatest. Collectively, our data demonstrate that lysine acetylation inhibits translation, most likely by interfering with subunit association. These results have also uncovered a new mechanism for coupling translation to the metabolic state of the cell. IMPORTANCENumerous cellular processes are regulated in response to the metabolic state of the cell. One such regulatory mechanism involves lysine acetylation, a covalent modification involving the transfer of an acetyl group from the central metabolites acetyl coenzyme A or acetyl phosphate to a lysine residue in a protein. This post-translational modification is known to regulate some central metabolic enzymes and transcription factors in bacteria, though a comprehensive understanding of its effect on cellular physiology is still lacking. In the present study, lysine acetylation was also found to inhibit translation in Escherichia coli by impeding ribosome association, most likely by disrupting salt-bridges along the binding interface of the 30S and 50S ribosomal subunits. These results further our understanding of lysine acetylation by uncovering a new target of regulation, protein synthesis, and aid in the design of bacteria for biotechnology applications where the growth conditions are known to promote lysine acetylation.