title: Vibrio spp. secrete proaerolysin as a folded dimer without the need for disulphide bond formation.
abstract: Proaerolysin is an extracellular dimeric protein that is secreted across the inner and outer membranes of Aeromonas spp. in separate steps. To investigate the role of protein folding in the second step, one or more cysteine residues were introduced and the mutant proaerolysins were expressed in Aeromonas hydrophila and Aeromonas salmonicida, as well as Vibrio cholerae. Replacing Met-41 with Cys resulted in expression of a protein that could form a dimer in which the monomers were linked together by a disulphide bridge. A double mutant was also made, in which Gly-202 and Ile-445 were replaced with cysteine in order to allow the formation of an intrachain disulphide bridge when the molecule was correctly folded. The M41C covalent dimer and G202C/I445C proaerolysin with the new intrachain bridge were both easily detected inside the bacteria, and they later appeared in the culture supernatants. Small amounts of incorrectly folded proaerolysin were also observed in the cells, but they were not secreted. We observed in the cells, but they were not secreted. We conclude that proaerolysin folds and dimerizes before being released from the cell, and that correct folding is a requirement for secretion to occur. The proton ionophore CCCP reduced release of the folded proteins. Unoxidized protein was secreted by cells grown in beta-mercaptoethanol and by a dsbA mutant of V. cholerae, indicating that disulphide bond formation may not be essential for release.
authors.affiliation: Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada.
authors.forename: K R
authors.initials: KR
authors.lastname: Hardie
authors.forename: A
authors.initials: A
authors.lastname: Schulze
authors.forename: M W
authors.initials: MW
authors.lastname: Parker
authors.forename: J T
authors.initials: JT
authors.lastname: Buckley
mesh_terms: D000333:Aeromonas / Q000235:genetics / Q000502:physiology*; D016980:Aeromonas hydrophila / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D003545:Cysteine / Q000737:chemistry*; D003553:Cystine / Q000737:chemistry; D004229:Dithiothreitol / Q000494:pharmacology; D004926:Escherichia coli / Q000378:metabolism; D007535:Isomerases / Q000235:genetics / Q000378:metabolism; D008623:Mercaptoethanol / Q000494:pharmacology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D052899:Pore Forming Cytotoxic Proteins; D011487:Protein Conformation; D019704:Protein Disulfide-Isomerases; D017510:Protein Folding; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D014734:Vibrio cholerae / Q000235:genetics / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D052899:Pore Forming Cytotoxic Proteins; D011498:Protein Precursors; D011994:Recombinant Proteins; D013439:Sulfhydryl Reagents; D003553:Cystine; C032676:aerolysin; D008623:Mercaptoethanol; D007535:Isomerases; D019704:Protein Disulfide-Isomerases; D003545:Cysteine; D004229:Dithiothreitol