title: Bacterial secretins form constitutively open pores akin to general porins.
abstract: Proteins called secretins form large multimeric complexes that are essential for macromolecular transit across the outer membrane of Gram-negative bacteria. Evidence suggests that the channels formed by some secretin complexes are not tightly closed, but their permeability properties have not been well characterized. Here, we used cell-free synthesis coupled with spontaneous insertion into liposomes to investigate the permeability of the secretin PulD. Leakage assays using preloaded liposomes indicated that PulD allows the efflux of small fluorescent molecules with a permeation cutoff similar to that of general porins. Other secretins were also found to form similar pores. To define the polypeptide region involved in determining the pore size, we analyzed a collection of PulD variants and studied the roles of gates 1 and 2, which were previously reported to affect the pore size of filamentous phage f1 secretin pIV, in assembly and pore formation. Liposome leakage and a novel in vivo assay showed that replacement of the conserved proline residue at position 443 in PulD by leucine increased the apparent size of the pore. The in vitro approach described here could be used to study the pore properties of membrane proteins whose production in vivo is toxic.
authors.affiliation: Université de Paris-Sud, Institut de Biochimie et de Biophysique Moléculaire et Cellulaire, Orsay, France.
authors.forename: Elena
authors.initials: E
authors.lastname: Disconzi
authors.forename: Ingrid
authors.initials: I
authors.lastname: Guilvout
authors.forename: Mohamed
authors.initials: M
authors.lastname: Chami
authors.forename: Muriel
authors.initials: M
authors.lastname: Masi
authors.forename: Gerard H M
authors.initials: GH
authors.lastname: Huysmans
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Pugsley
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bayan
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D010539:Permeability; D018272:Porins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; D008081:Liposomes; D018272:Porins; C560058:PulD protein, E coli