title: Hydration dependent dynamics in sol-gel encapsulated myoglobin.
abstract: In this work we study the effect of hydration on the dynamics of a protein in confined geometry, i.e. encapsulated in a porous silica matrix. Using elastic neutron scattering we investigate the temperature dependence of the mean square displacements of non-exchangeable hydrogen atoms of sol-gel encapsulated met-myoglobin. The study is extended to samples at 0.2, 0.3 and 0.5 g water/g protein fractions and comparison is made with met-myoglobin powders at the same average hydration and with a dry powder sample. Elastic data are analysed using a model of dynamical heterogeneity to take into account deviations of elastic intensity from gaussian behaviour in a large momentum transfer range and reveal a specific, model independent, effect of sol-gel confinement on protein dynamics, consisting mainly in a reduction of large-scale motions that are activated at temperatures larger than approximately 230 K. Surprisingly, the effect of confinement depends markedly on hydration and has a maximum at about 35% water/protein fraction corresponding to full first shell hydration. The presence of hydration-dependent MSD also in encapsulated met-Mb strongly supports the idea that the effect of sol-gel confinement on protein dynamics involves a modification of the structural/dynamical properties of the co-encapsulated solvent more than direct protein-matrix interactions.
authors.affiliation: Department of Physical and Astronomical Sciences, CNISM and University of Palermo, Via Archirafi, 36, 90123 Palermo, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Schirò
authors.forename: Michele
authors.initials: M
authors.lastname: Sclafani
authors.forename: Francesca
authors.initials: F
authors.lastname: Natali
authors.forename: Antonio
authors.initials: A
authors.lastname: Cupane
mesh_terms: D000818:Animals; D004548:Elasticity; D005782:Gels; D006859:Hydrogen; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism; D033363:Neutron Diffraction; D013696:Temperature; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005782:Gels; D009211:Myoglobin; D014867:Water; D006859:Hydrogen