title: Pressure-induced protein unfolding in the ternary system AOT-octane-water is different from that in bulk water.
abstract: In a cellular environment, the presence of macromolecular cosolutes and membrane interfaces can influence the folding-unfolding behavior of proteins. Here we report on the pressure stability of alpha-chymotrypsin in the ternary system bis(2-ethylhexyl)sodium sulfosuccinate-octane-water using FTIR spectroscopy. The ternary system forms anionic reverse micelles which mimic cellular conditions. We find that inclusion of a single protein molecule in a reverse micelle does not alter its conformation. When pressurized in bulk water, alpha-chymotrypsin unfolds at 750 MPa into a partially unfolded structure. In contrast, in the ternary system, the same pressure increase induces a random coil-like unfolded state, which collapses into an amorphous aggregate during the decompression phase. It is suggested that the unfolding pathway is different in a cell-mimicking environment due to the combined effect of multiple factors, including confinement. A phase transition of the reverse micellar to the lamellar phase is thought to be essential to provide the conditions required for unfolding and aggregation, though the unfolding is not a direct result of the phase transition. Our observations therefore suggest that membranes may cause the formation of alternative conformations that are more susceptible to aggregation.
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom. fpsm2@cam.ac.uk
authors.forename: Filip
authors.initials: F
authors.lastname: Meersman
authors.forename: Carolien
authors.initials: C
authors.lastname: Dirix
authors.forename: Stepan
authors.initials: S
authors.lastname: Shipovskov
authors.forename: Natalia L
authors.initials: NL
authors.lastname: Klyachko
authors.forename: Karel
authors.initials: K
authors.lastname: Heremans
mesh_terms: D000818:Animals; D002918:Chymotrypsin / Q000737:chemistry* / Q000378:metabolism; D004143:Dioctyl Sulfosuccinic Acid / Q000737:chemistry*; D008823:Micelles; D018716:Molecular Mimicry; D009795:Octanes / Q000737:chemistry*; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D008823:Micelles; D009795:Octanes; D011506:Proteins; D014867:Water; D004143:Dioctyl Sulfosuccinic Acid; D002918:Chymotrypsin; C117608:alpha-chymotrypsin; C026728:octane