On the Mechanism of Peptidoglycan Binding and Cleavage by the endo-Specific Lytic Transglycosylase MltE from Escherichia coli

Guntur Fibriansah, Francesca I. Gliubich, Andy-Mark W. H. Thunnissen*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

The lytic transglycosylase MltE from Escherichia coli. is a periplasmic, outer membrane-attached enzyme that cleaves the beta-1,4-glycosidic bonds between N-acetylmuramic acid and N-acetylglucosamine residues in the cell wall peptidoglycan, producing 1,6-anhydromuropeptides. Here we report three crystal structures of MltE: in a substrate-free state, in a binary complex with chitopentaose, and in a ternary complex with the glycopeptide inhibitor bulgecin A and the murodipeptide N-acetylglucosaminyl-N-acetylmuramy-L-Ala-D-Glu. The substrate-bound structures allowed a detailed analysis of the saccharicle-binding interactions in six subsites of the peptidoglycan-binding groove (subsites -4 to +2) and, combined with site-directed mutagenesis analysis, confirmed the role of Glu64 as catalytic acid/base. The structures permitted the precise modeling of a short glycan strand of eight saccharide residues, providing evidence for two additional subsites (+3 and +4) and revealing the productive conformational state of the substrate at subsites -1 and +1, where the glycosidic bond is cleaved. Full accessibility of the peptidoglycan-binding groove and preferential binding of an N-acetylmuramic acid residue in a C-4(1) chair conformation at subsite +2 explain why MltE shows only endo- and no exo-specific activity toward glycan strands. The results further indicate that catalysis of glycosidic bond cleavage by MltE proceeds Via distortion toward a sofa like conformation of the N-acetylmuramic acid sugar ring at subsite -1 and by anchimeric assistance Of the sugar's N-acetyl group, as shown previously for the lytic transglycosylases Slt70 and MltB.

Original languageEnglish
Pages (from-to)9164-9177
Number of pages14
JournalBiochemistry
Volume51
Issue number45
DOIs
Publication statusPublished - 13-Nov-2012

Keywords

  • MOLECULAR REPLACEMENT
  • CRYSTAL-STRUCTURES
  • CATALYTIC DOMAIN
  • DIFFRACTION DATA
  • CELL-WALL
  • CRYSTALLOGRAPHY
  • IDENTIFICATION
  • REFINEMENT
  • GENERATION
  • HYDROLASES

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