title: Aeropin from the extremophile Pyrobaculum aerophilum bypasses the serpin misfolding trap.
abstract: Serpins are metastable proteinase inhibitors. Serpin metastability drives both a large conformational change that is utilized during proteinase inhibition and confers an inherent structural flexibility that renders serpins susceptible to aggregation under certain conditions. These include point mutations (the basis of a number of important human genetic diseases), small changes in pH, and an increase in temperature. Many studies of serpins from mesophilic organisms have highlighted an inverse relationship: mutations that confer a marked increase in serpin stability compromise inhibitory activity. Here we present the first biophysical characterization of a metastable serpin from a hyperthermophilic organism. Aeropin, from the archaeon Pyrobaculum aerophilum, is both highly stable and an efficient proteinase inhibitor. We also demonstrate that because of high kinetic barriers, aeropin does not readily form the partially unfolded precursor to serpin aggregation. We conclude that stability and activity are not mutually exclusive properties in the context of the serpin fold, and propose that the increased stability of aeropin is caused by an unfolding pathway that minimizes the formation of an aggregation-prone intermediate ensemble, thereby enabling aeropin to bypass the misfolding fate observed with other serpins.
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia.
authors.forename: Lisa D
authors.initials: LD
authors.lastname: Cabrita
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia.
authors.forename: James A
authors.initials: JA
authors.lastname: Irving
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia.
authors.forename: Mary C
authors.initials: MC
authors.lastname: Pearce
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia; ARC Centre of Excellence for Structural and Function Microbial Genomics, Monash University, Clayton 3800, Australia. Electronic address: james.whisstock@med.monash.edu.au.
authors.forename: James C
authors.initials: JC
authors.lastname: Whisstock
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia. Electronic address: steve.bottomley@med.monash.edu.au.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Bottomley
mesh_terms: D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D002942:Circular Dichroism; D004220:Disulfides / Q000737:chemistry; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D017510:Protein Folding; D041543:Pyrobaculum / Q000737:chemistry*; D015842:Serine Proteinase Inhibitors / Q000737:chemistry*; D015843:Serpins / Q000737:chemistry*
chemical_list: D004220:Disulfides; D015842:Serine Proteinase Inhibitors; D015843:Serpins