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Updated: Aug 4, 2026

From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
Published on: July 4, 2016
Doughnut-shaped structure of a bacterial muramidase revealed by X-ray crystallography
A M Thunnissen1, A J Dijkstra, K H Kalk
1BIOSON Research Institute, Department of Chemistry, University of Groningen, The Netherlands.
Abstract:
The integrity of the bacterial cell wall depends on the balanced action of several peptidoglycan (murein) synthesizing and degrading enzymes. Penicillin inhibits the enzymes responsible for peptide crosslinks in the peptidoglycan polymer. Enzymes that act solely on the glycosidic bonds are insensitive to this antibiotic, thus offering a target for the design of antibiotics distinct from the beta-lactams. Here we report the X-ray structure of the periplasmic soluble lytic transglycosylase (SLT; M(r) 70,000) from Escherichia coli. This unique bacterial exomuramidase cleaves the beta-1,4-glycosidic bonds of peptidoglycan to produce small 1,6-anhydromuropeptides. The structure of SLT reveals a 'superhelical' ring of alpha-helices with a separate domain on top which resembles the fold of lysozyme. Site-directed mutagenesis and a crystallographic inhibitor-binding study confirmed that the lysozyme-like domain contains the active site of SLT.
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