title: Temperature-dependent dynamics of dry and hydrated β-casein studied by quasielastic neutron scattering.
abstract: β-Casein is a component of casein micelle with amphillic nature and is recognized as a "natively disordered" protein that lacks secondary structures. In this study, the temperature and hydration effects on the dynamics of β-casein are explored by quasielastic neutron scattering (QENS). An upturn in the mean square displacement (MSD) of hydrated β-casein indicates an increase of protein flexibility at a temperature of ~225 K. Another increase in MSD at ~100 K, observed in both dry and hydrated β-casein, is ascribed to the methyl group rotations, which are not sensitive to hydration. QENS analysis in the energy domain reveals that the fraction of hydrogen atoms participating in motion in a sphere of diffusion is highly hydration dependent and increases with temperature. In the time domain analysis, a logarithmic-like decay is observed in the range of picosecond to nanosecond (β-relaxation time) in the dynamics of hydrated β-casein. This dynamical behavior has been observed in hydrated globular and oligomeric proteins. Our temperature-dependent QENS experiments provide evidence that lack of a secondary structure in β-casein results in higher flexibility in its dynamics and easier reversible thermal unfolding compared to other rigid biomolecules.
authors.affiliation: Department of Physics and Astronomy, Wayne State University , Detroit, Michigan 48201, United States.
authors.forename: Gurpreet K
authors.initials: GK
authors.lastname: Dhindsa
authors.forename: Madhusudan
authors.initials: M
authors.lastname: Tyagi
authors.forename: Xiang-qiang
authors.initials: XQ
authors.lastname: Chu
mesh_terms: D002364:Caseins / Q000737:chemistry*; D017666:Deuterium Oxide / Q000737:chemistry; D004058:Diffusion; D006859:Hydrogen / Q000737:chemistry; D033363:Neutron Diffraction; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D002364:Caseins; D014867:Water; D006859:Hydrogen; D017666:Deuterium Oxide