Abstract
In order to establish the sequence dependence of RimJ-mediated protein N-terminal acetylation in E. coli, the Z-domain variants differing by the second or third amino acid residue were expressed and analyzed by mass spectrometry. Only subsequent to the initiating methionine residue cleavage, the RimJ-catalyzed N-terminal acetylation mainly occurred at the N-terminal serine and threonine residues and was significantly enhanced by hydrophobic or negatively charged residues in the penultimate position.
Highlights
The initial stage of protein maturation involves the processing of the N-terminal end of newly synthesized polypeptide chain in both prokaryotes and eukaryotes [1]
The intiating N-formylmethionine residue is deformylated by peptide deformylase in most proteins and the resulting methionine (Met1) residue is cleaved by methionine aminopeptidases (MAP) in a significant fraction of total proteins [2]
Each of the purified Z-domain variants differing by the second or third amino acid residue was analyzed by electrospray ionization mass spectrometry (ESI-MS) and subsequent deconvolution of multiple-charged protein ions as shown in Figure 1 and Figure 2, respectively
Summary
The initial stage of protein maturation involves the processing of the N-terminal end of newly synthesized polypeptide chain in both prokaryotes and eukaryotes [1]. In a few endogenous bacterial proteins, the N-terminal residues after the Met cleavage are subsequently acetylated by the corresponding N-acetyltranferases (NATs) [3]-[5]. In Escherichia coli, the ribosomal proteins S18, S5 and L7/L12 are Nα-acetylated by their corresponding NATs, RimI, RimJ, and RimL, respectively [6] [7]. The functional relevance of the Nα-acetyl group in these Nα-acetylated endogenous proteins is unclear since no phenotypic difference was observed in the bacterial cells in which the NAT genes were deleted. In eukaryotes Nα-acetylation is prevalent and plays a significant role in the stability, activity and tar-
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