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AlgK is a TPR-containing protein and the periplasmic component of a novel exopolysaccharide secretin

Carrie-Lynn Keiski1, Michael Harwich, Sumita Jain

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

Structure (London, England : 1993)
|February 18, 2010
PubMed

Insights

Pseudomonas aeruginosa uses AlgK, an outer membrane lipoprotein, to produce high molecular weight alginate, crucial for chronic biofilm infections in cystic fibrosis patients. AlgK aids alginate complex assembly and outer membrane secretin function.

Area of Science:

  • Microbiology
  • Structural Biology
  • Biochemistry

Background:

  • Pseudomonas aeruginosa is an opportunistic pathogen causing chronic biofilm infections, particularly in cystic fibrosis patients.
  • During lung colonization, P. aeruginosa exhibits a mucoid phenotype marked by alginate overproduction, an exopolysaccharide essential for biofilm structure.

Purpose of the Study:

  • To elucidate the structural and functional role of AlgK in alginate production and outer membrane protein localization.
  • To investigate the potential involvement of AlgK in a novel outer membrane secretin system.

Main Methods:

  • X-ray crystallography was used to determine the 2.5 Å structure of AlgK.
  • Bioinformatics analysis was employed to compare AlgK topology with related proteins involved in exopolysaccharide synthesis.
  • Protein-protein interaction sites were identified through structural analysis.

Main Results:

  • AlgK is identified as an outer membrane lipoprotein essential for high molecular weight alginate production.
  • The structure of AlgK reveals 9.5 tetratricopeptide-like repeats and potential protein-protein interaction sites.
  • AlgK contributes to the proper localization of the porin AlgE and shares topological similarities with proteins involved in other exopolysaccharide systems (BcsA, PgaA, PelB).

Conclusions:

  • AlgK plays a critical role in the assembly of the alginate biosynthetic complex.
  • AlgK represents a periplasmic component of a novel outer membrane secretin, distinct from canonical bacterial polysaccharide secretion systems.

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