title: How osmolytes influence hydrophobic polymer conformations: A unified view from experiment and theory.
abstract: It is currently the consensus belief that protective osmolytes such as trimethylamine N-oxide (TMAO) favor protein folding by being excluded from the vicinity of a protein, whereas denaturing osmolytes such as urea lead to protein unfolding by strongly binding to the surface. Despite there being consensus on how TMAO and urea affect proteins as a whole, very little is known as to their effects on the individual mechanisms responsible for protein structure formation, especially hydrophobic association. In the present study, we use single-molecule atomic force microscopy and molecular dynamics simulations to investigate the effects of TMAO and urea on the unfolding of the hydrophobic homopolymer polystyrene. Incorporated with interfacial energy measurements, our results show that TMAO and urea act on polystyrene as a protectant and a denaturant, respectively, while complying with Tanford-Wyman preferential binding theory. We provide a molecular explanation suggesting that TMAO molecules have a greater thermodynamic binding affinity with the collapsed conformation of polystyrene than with the extended conformation, while the reverse is true for urea molecules. Results presented here from both experiment and simulation are in line with earlier predictions on a model Lennard-Jones polymer while also demonstrating the distinction in the mechanism of osmolyte action between protein and hydrophobic polymer. This marks, to our knowledge, the first experimental observation of TMAO-induced hydrophobic collapse in a ternary aqueous system.
authors.affiliation: Department of Chemistry, Columbia University, New York, NY 10027; TIFR Centre for Interdisciplinary Sciences, Narsingi, Hyderabad 500075, India;
authors.forename: Jagannath
authors.initials: J
authors.lastname: Mondal
authors.affiliation: Department of Chemistry, University of Toronto, ON, Canada M5S 3HS;
authors.forename: Duncan
authors.initials: D
authors.lastname: Halverson
authors.affiliation: Department of Chemistry, University of Toronto, ON, Canada M5S 3HS;
authors.forename: Isaac T S
authors.initials: IT
authors.lastname: Li
authors.affiliation: CNRS - Institut de Biologie Physico-Chimique - PSL Research University, Laboratoire de Biochimie Théorique, 75005 Paris, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Stirnemann
authors.affiliation: Department of Chemistry, University of Toronto, ON, Canada M5S 3HS;
authors.forename: Gilbert C
authors.initials: GC
authors.lastname: Walker
authors.affiliation: Department of Chemistry, Columbia University, New York, NY 10027; bb8@columbia.edu.
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Berne
mesh_terms: D003198:Computer Simulation; D057927:Hydrophobic and Hydrophilic Interactions; D008744:Methylamines / Q000737:chemistry; D018625:Microscopy, Atomic Force; D056004:Molecular Dynamics Simulation; D016011:Normal Distribution; D011108:Polymers / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry; D012984:Software; D012997:Solvents / Q000737:chemistry; D013314:Stress, Mechanical; D013816:Thermodynamics; D014508:Urea / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D008744:Methylamines; D011108:Polymers; D011137:Polystyrenes; D011506:Proteins; D012997:Solvents; D014867:Water; D014508:Urea; C005855:trimethyloxamine
keywords: TMAO; free energy; preferential binding; single-molecule force spectroscopy; urea