A Major Portion of DNA Gyrase Inhibitor Microcin B17 Undergoes an N,O-Peptidyl Shift during Synthesis

Dmitry Ghilarov,Marina Serebryakova,Irina Shkundina,Konstantin Severinov

doi:10.1074/jbc.m111.241315

Abstract

Microcin B17 (McB) is a 43-amino acid antibacterial peptide targeting the DNA gyrase. The McB precursor is ribosomally produced and then post-translationally modified by the McbBCD synthase. Active mature McB contains eight oxazole and thiazole heterocycles. Here, we show that a major portion of mature McB contains an additional unusual modification, a backbone ester bond connecting McB residues 51 and 52. The modification results from an N → O shift of the Ser(52) residue located immediately downstream of one of McB thiazole heterocycles. We speculate that the N,O-peptidyl shift undergone by Ser(52) is an intermediate of post-translational modification reactions catalyzed by the McbBCD synthase that normally lead to formation of McB heterocycles.

Highlights

Microcins are small (Ͻ10 kDa) antibacterial peptides produced by enterobacteria
The new structure is characterized by the presence of depsipeptide bond between microcin B17 (McB) residues 51 and 52
The presence of depsipeptide bond explains the discrepancy of the dominating MS-MS X-type ion with a value calculated based on standard McB structure

Summary

Introduction

Microcins are small (Ͻ10 kDa) antibacterial peptides produced by enterobacteria. They are synthesized on the ribosomes, and some are subject to complex post-translational modifications [1, 2]. MALDI-MS analysis revealed that the first two HPLC peaks contained mass-ions with m/z ϭ 3094 and correspond to fully matured 8-cycle compound shown in Fig. 1 and previously termed McB ⌬0 [15].

Results

Conclusion