title: Folding mechanism of the metastable serpin α1-antitrypsin.
abstract: The misfolding of serpins is linked to several genetic disorders including emphysema, thrombosis, and dementia. During folding, inhibitory serpins are kinetically trapped in a metastable state in which a stretch of residues near the C terminus of the molecule are exposed to solvent as a flexible loop (the reactive center loop). When they inhibit target proteases, serpins transition to a stable state in which the reactive center loop forms part of a six-stranded β-sheet. Here, we use hydrogen-deuterium exchange mass spectrometry to monitor region-specific folding of the canonical serpin human α(1)-antitrypsin (α(1)-AT). We find large differences in the folding kinetics of different regions. A key region in the metastable → stable transition, β-strand 5A, shows a lag phase of nearly 350 s. In contrast, the "B-C barrel" region shows no lag phase and the incorporation of the C-terminal residues into β-sheets B and C is largely complete before the center of β-sheet A begins to fold. We propose this as the mechanism for trapping α(1)-AT in a metastable form. Additionally, this separation of timescales in the folding of different regions suggests a mechanism by which α(1)-AT avoids polymerization during folding.
authors.affiliation: Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Tsutsui
authors.forename: Richard
authors.initials: R
authors.lastname: Dela Cruz
authors.forename: Patrick L
authors.initials: PL
authors.lastname: Wintrode
mesh_terms: D002621:Chemistry / Q000379:methods; D006801:Humans; D006859:Hydrogen / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D015843:Serpins / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D053719:Tandem Mass Spectrometry / Q000379:methods; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry; D000515:alpha 1-Antitrypsin / Q000737:chemistry*
chemical_list: D011108:Polymers; D015843:Serpins; D012997:Solvents; D000515:alpha 1-Antitrypsin; D006859:Hydrogen; D014364:Tryptophan