RimJ is responsible for Nα-acetylation of thymosin α1 in Escherichia coli

N α-Acetylation is one of the most common protein modifications in eukaryotes but a rare event in prokaryotes. Some endogenously N α-acetylated proteins in eukaryotes are frequently reported not to be acetylated or only very partially when expressed in recombinant Escherichia coli. Thymosin α1 (Tα1), an N α-acetylated peptide of 28 amino acids, displays a powerful general immunostimulating activity. Here, we revealed that a fusion protein of thymosin α1 and L12 is partly N α-acetylated in E. coli. Through deletion of some N α-acetyltransferases by Red recombination, we found that, when rimJ is disrupted, the fusion protein is completely unacetylated. The relationship of rimJ and N α-acetylation of Tα1 was further investigated by gene rescue and in vitro modification. Our results demonstrate that N α-acetylation of recombinant Tα1-fused protein in E. coli is catalyzed by RimJ and that fully acetylated Tα1 can be obtained by co-expressing with RimJ. This is the first description that an ectopic protein acetylation in bacterial expression systems is catalyzed by RimJ, a known prokaryotic N α-acetyltransferase.