title: A redox-sensitive loop regulates plasminogen activator inhibitor type 2 (PAI-2) polymerization.
abstract: Plasminogen activator inhibitor type 2 (PAI-2) is the only wild-type serpin that polymerizes spontaneously under physiological conditions. We show that PAI-2 loses its ability to polymerize following reduction of thiol groups, suggesting that an intramolecular disulfide bond is essential for the polymerization. A novel disulfide bond was identified between C79 (in the CD-loop) and C161 (at the bottom of helix F). Substitution mutants in which this disulfide bond was broken did not polymerize. Reactive center loop peptide insertion experiments and binding of bis-ANS to hydrophobic cavities indicate that the C79-C161 disulfide bond stabilizes PAI-2 in a polymerogenic conformation with an open A-beta-sheet. Elimination of this disulfide bond causes A-beta-sheet closure and abrogates the polymerization. The finding that cytosolic PAI-2 is mostly monomeric, whereas PAI-2 in the secretory pathway is prone to polymerize, suggests that the redox status of the cell could regulate PAI-2 polymerization. Taken together, our data suggest that the CD-loop functions as a redox-sensitive switch that converts PAI-2 between an active stable monomeric and a polymerogenic conformation, which is prone to form inactive polymers.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umeå University, 901 87 Umeå, Sweden.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Wilczynska
authors.forename: Sergei
authors.initials: S
authors.lastname: Lobov
authors.forename: Per-Ingvar
authors.initials: PI
authors.lastname: Ohlsson
authors.forename: Tor
authors.initials: T
authors.lastname: Ny
mesh_terms: D003545:Cysteine / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D017396:Plasminogen Activator Inhibitor 2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011108:Polymers / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D004220:Disulfides; D010455:Peptides; D017396:Plasminogen Activator Inhibitor 2; D011108:Polymers; D003545:Cysteine