Biochemical evidence for relaxed substrate specificity of Nα-acetyltransferase (Rv3420c/rimI) of Mycobacterium tuberculosis.

Deepika Pathak,Aadil Hussain Bhat,Vandana Sapehia,Alka Rao,Jagdish Rai

doi:10.1038/srep28892

Deepika Pathak, Aadil Hussain Bhat + Show 3 more

Open Access

https://doi.org/10.1038/srep28892

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Abstract

Nα-acetylation is a naturally occurring irreversible modification of N-termini of proteins catalyzed by Nα-acetyltransferases (NATs). Although present in all three domains of life, it is little understood in bacteria. The functional grouping of NATs into six types NatA - NatF, in eukaryotes is based on subunit requirements and stringent substrate specificities. Bacterial orthologs are phylogenetically divergent from eukaryotic NATs, and only a couple of them are characterized biochemically. Accordingly, not much is known about their substrate specificities. Rv3420c of Mycobacterium tuberculosis is a NAT ortholog coding for RimIMtb. Using in vitro peptide-based enzyme assays and mass-spectrometry methods, we provide evidence that RimIMtb is a protein Nα-acetyltransferase of relaxed substrate specificity mimicking substrate specificities of eukaryotic NatA, NatC and most competently that of NatE. Also, hitherto unknown acetylation of residues namely, Asp, Glu, Tyr and Leu by a bacterial NAT (RimIMtb) is elucidated, in vitro. Based on in vivo acetylation status, in vitro assay results and genetic context, a plausible cellular substrate for RimIMtb is proposed.

Highlights

Appreciated once in eukaryotes only, Nα-acetylation of proteins appears quintessential in all three domains of life
Protein Nα-acetylation is a co/post-translational modification that is implicated in a variety of cellular processes and regulation thereof, in eukaryotes, but it is little understood in bacteria
Enzymes belonging to GNAT family of proteins that acetylate amino group of aminoglycosides are well known in mycobacteria

Summary

Introduction

Appreciated once in eukaryotes only, Nα-acetylation of proteins appears quintessential in all three domains of life. Sequence analysis of mycobacterial Nα-acetylated peptides suggests the presence of at least one NAT with eukaryotic NatA-like substrate specificity that is involved in acetylating approximately 84% of the protein substrates (Supplementary Figure S1).

Results

Conclusion