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Generation of Alginate Microspheres for Biomedical Applications
10:33

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Published on: August 12, 2012

Structural basis for alginate secretion across the bacterial outer membrane.

John C Whitney1, Iain D Hay, Canhui Li

  • 1Molecular Structure and Function, The Hospital for Sick Children, Toronto, ON, Canada M5G 1X8.

Proceedings of the National Academy of Sciences of the United States of America
|July 23, 2011
PubMed
Summary

The outer membrane protein AlgE facilitates alginate export in Pseudomonas aeruginosa, crucial for cystic fibrosis lung infections. Its structure reveals a unique pore regulated by loop T8, controlling exopolysaccharide secretion.

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08:57

Identification of Novel Genes Associated with Alginate Production in Pseudomonas aeruginosa Using Mini-himar1 Mariner Transposon-mediated Mutagenesis

Published on: March 10, 2014

Area of Science:

  • Microbiology
  • Structural Biology
  • Biochemistry

Background:

  • Pseudomonas aeruginosa is a major cause of chronic lung infections in cystic fibrosis patients.
  • Alginate overproduction by P. aeruginosa leads to a mucoid phenotype, contributing to lung colonization.
  • The outer membrane protein AlgE is hypothesized to mediate alginate secretion across the bacterial outer membrane.

Purpose of the Study:

  • To determine the crystal structure of the outer membrane protein AlgE.
  • To elucidate the mechanism of alginate export through AlgE.
  • To investigate the role of specific AlgE loops in transport regulation.

Main Methods:

  • X-ray crystallography to obtain the 2.3 Å structure of AlgE.
  • Site-directed mutagenesis to create loop deletion mutants (ΔT8-AlgE, ΔL2-AlgE).
  • Anion flux assays and in vivo complementation experiments.

Main Results:

  • The crystal structure revealed AlgE as a monomeric 18-stranded β-barrel with an electropositive pore constriction.
  • An arginine-rich conduit in the pore likely acts as a selectivity filter for alginate.
  • Deletion of periplasmic loop T8 significantly increased anion flux, suggesting its regulatory role in transport.
  • Complementation studies with ΔT8-AlgE impaired alginate production in vivo.

Conclusions:

  • AlgE forms a regulated transport pathway for alginate export across the outer membrane.
  • Periplasmic loop T8 plays a critical role in regulating AlgE-mediated transport.
  • This export mechanism differs from canonical capsular polysaccharide export systems like Wza.