title: Counteracting chemical chaperone effects on the single-molecule α-synuclein structural landscape.
abstract: Protein structure and function depend on a close interplay between intrinsic folding energy landscapes and the chemistry of the protein environment. Osmolytes are small-molecule compounds that can act as chemical chaperones by altering the environment in a cellular context. Despite their importance, detailed studies on the role of these chemical chaperones in modulating structure and dimensions of intrinsically disordered proteins have been limited. Here, we used single-molecule Förster resonance energy transfer to test the counteraction hypothesis of counterbalancing effects between the protecting osmolyte trimethylamine-N-oxide (TMAO) and denaturing osmolyte urea for the case of α-synuclein, a Parkinson's disease-linked protein whose monomer exhibits significant disorder. The single-molecule experiments, which avoid complications from protein aggregation, do not exhibit clear solvent-induced cooperative protein transitions for these osmolytes, unlike results from previous studies on globular proteins. Our data demonstrate the ability of TMAO and urea to shift α-synuclein structures towards either more compact or expanded average dimensions. Strikingly, the experiments directly reveal that a 21 [urea][TMAO] ratio has a net neutral effect on the protein's dimensions, a result that holds regardless of the absolute osmolyte concentrations. Our findings shed light on a surprisingly simple aspect of the interplay between urea and TMAO on α-synuclein in the context of intrinsically disordered proteins, with potential implications for the biological roles of such chemical chaperones. The results also highlight the strengths of single-molecule experiments in directly probing the chemical physics of protein structure and disorder in more chemically complex environments.
authors: Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors: Allan Chris M
authors: AC
authors: Ferreon
authors: Mahdi Muhammad
authors: MM
authors: Moosa
authors: Yann
authors: Y
authors: Gambin
authors: Ashok A
authors: AA
authors: Deniz
mesh_terms: D031541:Fluorescence Resonance Energy Transfer; D008744:Methylamines / Q000737:chemistry; D018832:Molecular Chaperones / Q000737:chemistry*; D011487:Protein Conformation; D014508:Urea / Q000737:chemistry; D051844:alpha-Synuclein / Q000737:chemistry*
chemical_list: D008744:Methylamines; D018832:Molecular Chaperones; D051844:alpha-Synuclein; D014508:Urea; C005855:trimethyloxamine