title: Microscopic relaxations in a protein sustained down to 160K in a non-glass forming organic solvent.
abstract: We have studied microscopic dynamics of a protein in carbon disulfide, a non-glass forming solvent, down to its freezing temperature of ca. 160K.
  
  
  
  We have utilized quasielastic neutron scattering.
  
  
  
  A comparison of lysozyme hydrated with water and dissolved in carbon disulfide reveals a stark difference in the temperature dependence of the protein's microscopic relaxation dynamics induced by the solvent. In the case of hydration water, the common protein glass-forming solvent, the protein relaxation slows down in response to a large increase in the water viscosity on cooling down, exhibiting a well-known protein dynamical transition. The dynamical transition disappears in non-glass forming carbon disulfide, whose viscosity remains a weak function of temperature all the way down to freezing at just below 160K. The microscopic relaxation dynamics of lysozyme dissolved in carbon disulfide is sustained down to the freezing temperature of its solvent at a rate similar to that measured at ambient temperature.
  
  
  
  Our results demonstrate that protein dynamical transition is not merely solvent-assisted, but rather solvent-induced, or, more precisely, is a reflection of the temperature dependence of the solvent's glass-forming dynamics.
  
  
  
  We hypothesize that, if the long debated idea regarding the direct link between the microscopic relaxations and the biological activity in proteins is correct, then not only the microscopic relaxations, but also the activity, could be sustained in proteins all the way down to the freezing temperature of a non-glass forming solvent with a weak temperature dependence of its viscosity. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.
authors.affiliation: Chemical and Engineering Materials Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States. Electronic address: mamontove@ornl.gov.
authors.forename: E
authors.initials: E
authors.lastname: Mamontov
authors.affiliation: Biology and Soft Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States.
authors.forename: H
authors.initials: H
authors.lastname: O'Neill
mesh_terms: D004548:Elasticity; D005898:Glass / Q000737:chemistry*; D008853:Microscopy / Q000379:methods*; D009113:Muramidase / Q000737:chemistry*; D033363:Neutron Diffraction; D012997:Solvents / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D012997:Solvents; D014867:Water; D009113:Muramidase
keywords: Microscopic dynamics; Non-aqueous solvent; Protein