Structural basis for alginate secretion across the bacterial outer membrane

Journal Article · Tue Aug 09 00:00:00 EDT 2011 · Proceedings of the National Academy of Sciences of the United States of America

DOI:https://doi.org/10.1073/pnas.1104984108· OSTI ID:1040511

Whitney, J C; Robinson, H; Hay, I D; Li, C; Eckford, P D. W.; Amaya, M F; Wood, L F; Ohman, D E; Bear, C E; Rehm, B H; Howell, P L

Pseudomonas aeruginosa is the predominant pathogen associated with chronic lung infection among cystic fibrosis patients. During colonization of the lung, P. aeruginosa converts to a mucoid phenotype characterized by the overproduction of the exopolysaccharide alginate. Secretion of newly synthesized alginate across the outer membrane is believed to occur through the outer membrane protein AlgE. Here we report the 2.3 {angstrom} crystal structure of AlgE, which reveals a monomeric 18-stranded {beta}-barrel characterized by a highly electropositive pore constriction formed by an arginine-rich conduit that likely acts as a selectivity filter for the negatively charged alginate polymer. Interestingly, the pore constriction is occluded on either side by extracellular loop L2 and an unusually long periplasmic loop, T8. In halide efflux assays, deletion of loop T8 ({Delta}T8-AlgE) resulted in a threefold increase in anion flux compared to the wild-type or {Delta}L2-AlgE supporting the idea that AlgE forms a transport pathway through the membrane and suggesting that transport is regulated by T8. This model is further supported by in vivo experiments showing that complementation of an algE deletion mutant with {Delta}T8-AlgE impairs alginate production. Taken together, these studies support a mechanism for exopolysaccharide export across the outer membrane that is distinct from the Wza-mediated translocation observed in canonical capsular polysaccharide export systems.

• Research Organization: Brookhaven National Lab. (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE SC OFFICE OF SCIENCE (SC)
• DOE Contract Number: DE-AC02-98CH10886
• OSTI ID: 1040511
• Report Number(s): BNL-96314-2011-JA; PNASA6; R&D Project: BO-070; KP1605010; TRN: US201210%%687
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Vol. 108, Issue 32; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
60 APPLIED LIFE SCIENCES
ALGINATES
ANIONS
CRYSTAL STRUCTURE
EXPORTS
FIBROSIS
HALIDES
IN VIVO
LUNGS
MEMBRANE PROTEINS
MEMBRANES
MUTANTS
PATHOGENS
PHENOTYPE
POLYSACCHARIDES
PORINS
PSEUDOMONAS
SECRETION
TRANSLOCATION
URONIC ACIDS
VIRULENCE
biofilm
exopolysaccharide secretion
porin
virulence factor
uronic acids