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Updated: Feb 11, 2026
12:25
A Step-by-step Method for the Reconstitution of an ABC Transporter into Nanodisc Lipid Particles
Published on: August 31, 2012
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Periplasmic depolymerase provides insight into ABC transporter-dependent secretion of bacterial capsular
Sean D Liston1, Stephen A McMahon2, Audrey Le Bas3
1Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
Summary
Researchers discovered VexL, an enzyme that degrades Vi antigen, revealing that bacterial capsular polysaccharides are exposed to the periplasm during cell surface assembly via ATP-binding cassette (ABC) transporters.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Bacteria utilize capsular polysaccharides (CPSs) for virulence, with *Salmonella enterica* serovar Typhi producing Vi antigen.
- ATP-binding cassette (ABC) transporters facilitate CPS translocation to the bacterial cell surface.
- The exact mechanism of CPS cell-surface assembly via ABC transporters remains incompletely understood.
Purpose of the Study:
- To investigate the role of VexL, a pectate lyase homolog found in *Burkholderiales*, in Vi antigen processing and cell-surface assembly.
- To elucidate the structural features of VexL and its interaction with Vi antigen.
- To probe the conserved model of ABC transporter-dependent bacterial cell-surface polysaccharide export.
Main Methods:
- Identification of Vi antigen biosynthesis loci and VexL in *Burkholderiales*.
- Biochemical characterization of VexL activity, including pH optimum and metal dependence.
- X-ray crystallography of the VexL-Vi antigen complex at 1.22-Å resolution.
- Functional assays of VexL in *S. Typhi* to assess its localization and degradation activity.
Main Results:
- VexL was identified as a metal-independent endolyase specific for O-acetylated Vi antigen with an acidic pH optimum.
- The crystal structure revealed VexL's unique features for periplasmic localization and glycan binding, distinguishing it from secreted pectate lyases.
- VexL localized to the periplasm in *S. Typhi* and degraded Vi antigen, while a cytosolic form was ineffective unless export was blocked.
- Degradation of Vi antigen by periplasmic VexL indicates CPS exposure to the periplasm during ABC transporter-mediated export.
Conclusions:
- VexL is a novel enzyme involved in the processing or modification of Vi antigen in the periplasm.
- The study provides structural insights into VexL's substrate specificity and its role in bacterial cell-surface assembly.
- Findings support the model that capsular polysaccharides are translocated through the periplasm via ABC transporters before final cell surface exposure.
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