title: Dynamical transition in proteins and non-Gaussian behavior of low-frequency modes in self-consistent normal mode analysis.
abstract: Self-consistent normal mode analysis (SCNMA) is applied to heme c type cytochrome f to study temperature-dependent protein motion. Classical normal mode analysis assumes harmonic behavior and the protein mean-square displacement has a linear dependence on temperature. This is only consistent with low-temperature experimental results. To connect the protein vibrational motions between low and physiological temperatures, we have incorporated a fitted set of anharmonic potentials into SCNMA. In addition, quantum harmonic-oscillator theory has been used to calculate the displacement distribution for individual vibrational modes. We find that the modes involving soft bonds exhibit significant non-Gaussian dynamics at physiological temperature, which suggests that it may be the cause of the non-Gaussian behavior of the protein motions probed by elastic incoherent neutron scattering. The combined theory displays a dynamical transition caused by the softening of few "torsional" modes in the low-frequency regime ( <50 cm(-1) or <6 meV or >0.6 ps). These modes change from Gaussian to a classical distribution upon heating. Our theory provides an alternative way to understand the microscopic origin of the protein dynamical transition.
authors.affiliation: Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Jianguang
authors.initials: J
authors.lastname: Guo
authors.forename: Timo
authors.initials: T
authors.lastname: Budarz
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Ward
authors.forename: Earl W
authors.initials: EW
authors.lastname: Prohofsky
mesh_terms: D045348:Cytochromes f / Q000378:metabolism*; D008954:Models, Biological; D009068:Movement; D016011:Normal Distribution; D013696:Temperature
chemical_list: D045348:Cytochromes f