title: Oligomeric lipoprotein PelC guides Pel polysaccharide export across the outer membrane ofPseudomonas aeruginosa.
abstract: Secreted polysaccharides are important functional and structural components of bacterial biofilms. The opportunistic pathogenPseudomonas aeruginosaproduces the cationic exopolysaccharide Pel, which protects bacteria from aminoglycoside antibiotics and contributes to biofilm architecture through ionic interactions with extracellular DNA. A bioinformatics analysis of genome databases suggests that gene clusters for Pel biosynthesis are present in >125 bacterial species, yet little is known about how this biofilm exopolysaccharide is synthesized and exported from the cell. In this work, we characterize PelC, an outer membrane lipoprotein essential for Pel production. Crystal structures of PelC fromGeobacter metallireducensandParaburkholderia phytofirmanscoupled with structure-guided disulfide cross-linking inP. aeruginosasuggest that PelC assembles into a 12- subunit ring-shaped oligomer. In this arrangement, an aromatic belt in proximity to its lipidation site positions the highly electronegative surface of PelC toward the periplasm. PelC is structurally similar to theEscherichia coliamyloid exporter CsgG; however, unlike CsgG, PelC does not possess membrane-spanning segments required for polymer export across the outer membrane. We show that the multidomain protein PelB with a predicted C-terminal β-barrel porin localizes to the outer membrane, and propose that PelC functions as an electronegative funnel to guide the positively charged Pel polysaccharide toward an exit channel formed by PelB. Together, our findings provide insight into the unique molecular architecture and export mechanism of the Pel apparatus, a widespread exopolysaccharide secretion system found in environmental and pathogenic bacteria.
authors.affiliation: Program in Molecular Structure & Function, The Hospital for Sick Children, Toronto, ON, Canada M5G 0A4.|Department of Biochemistry, University of Toronto, Toronto, ON, Canada M5S 1A8.
authors.forename: Lindsey S
authors.initials: LS
authors.lastname: Marmont
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 1N4.
authors.forename: Jacquelyn D
authors.initials: JD
authors.lastname: Rich
authors.affiliation: Program in Molecular Structure & Function, The Hospital for Sick Children, Toronto, ON, Canada M5G 0A4.|Department of Biochemistry, University of Toronto, Toronto, ON, Canada M5S 1A8.
authors.forename: John C
authors.initials: JC
authors.lastname: Whitney
authors.affiliation: Program in Molecular Structure & Function, The Hospital for Sick Children, Toronto, ON, Canada M5G 0A4.|Department of Biochemistry, University of Toronto, Toronto, ON, Canada M5S 1A8.
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Whitfield
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 1N4.
authors.forename: Henrik
authors.initials: H
authors.lastname: Almblad
authors.affiliation: Photon Science Division, Brookhaven National Laboratory, Upton, NY 11973-5000.
authors.forename: Howard
authors.initials: H
authors.lastname: Robinson
authors.affiliation: Department of Microbiology, University of Washington, Seattle, WA 98195-7242.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Parsek
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 1N4.
authors.forename: Joe J
authors.identifier: 0000-0003-0368-9539
authors.initials: JJ
authors.lastname: Harrison
authors.affiliation: Program in Molecular Structure & Function, The Hospital for Sick Children, Toronto, ON, Canada M5G 0A4; howell@sickkids.ca.|Department of Biochemistry, University of Toronto, Toronto, ON, Canada M5S 1A8.
authors.forename: P Lynne
authors.initials: PL
authors.lastname: Howell
mesh_terms: D018441:Biofilms / Q000254:growth & development; D019295:Computational Biology; D018360:Crystallography, X-Ray; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D008074:Lipoproteins / Q000737:chemistry / Q000235:genetics; D019897:Periplasm / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011133:Polysaccharide-Lyases / Q000737:chemistry* / Q000235:genetics; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000737:chemistry* / Q000472:pathogenicity
chemical_list: D008074:Lipoproteins; D011135:Polysaccharides, Bacterial; D011133:Polysaccharide-Lyases; C023911:pectate lyase
keywords: PEL; Pseudomonas aeruginosa; X-ray crystallography; biofilms; exopolysaccharides