title: Ultrafast dynamics of nonequilibrium resonance energy transfer and probing globular protein flexibility of myoglobin.
abstract: Protein structural plasticity is critical to many biological activities and accurate determination of its temporal and spatial fluctuations is challenging and difficult. Here, we report our extensive characterization of global flexibility of a globular heme protein of myoglobin using resonance energy transfer as a molecular ruler. With site-directed mutagenesis, we use a tryptophan scan to examine local structural fluctuations from B to H helices utilizing 10 tryptophan-heme energy transfer pairs with femtosecond resolution. We observed ultrafast resonance energy transfer dynamics by following a nearly single exponential behavior in 10-100 ps, strongly indicating that the globular structure of myoglobin is relatively rigid, with no observable static or slow dynamic conformational heterogeneity. The observation is against our molecular dynamics simulations, which show large local fluctuations and give multiple exponential energy transfer behaviors, suggesting too flexible of the global structure and thus raising a serious issue of the force fields used in simulations. Finally, these ultrafast energy transfer dynamics all occur on the similar time scales of local environmental relaxations (solvation), leading to nonexponential processes caused by energy relaxations, not structural fluctuations. Our analyses of such processes reveal an intrinsic compressed- and/or stretched-exponential behaviors and elucidate the nature of inherent nonequilibrium of ultrafast resonance energy transfer in proteins. This new concept of compressed nonequilibrium transfer dynamics should be applied to all protein studies by time-resolved Förster resonance energy transfer (FRET).
authors.affiliation: Department of Physics, OSU Biophysics Program, 191 West Woodruff Avenue, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Stevens
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Link
authors.forename: Chen
authors.initials: C
authors.lastname: Zang
authors.forename: Lijuan
authors.initials: L
authors.lastname: Wang
authors.forename: Dongping
authors.initials: D
authors.lastname: Zhong
mesh_terms: D031541:Fluorescence Resonance Energy Transfer; D006418:Heme / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D016297:Mutagenesis, Site-Directed; D009211:Myoglobin / Q000737:chemistry* / Q000235:genetics; D018583:Pliability; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D013997:Time Factors; D014364:Tryptophan / Q000737:chemistry* / Q000235:genetics
chemical_list: D009211:Myoglobin; D011994:Recombinant Proteins; D012996:Solutions; D006418:Heme; D014364:Tryptophan