Elastic Scattering Spectroscopy (ESS): an Instrument-Concept for Dynamics of Complex (Bio-) Systems From Elastic Neutron Scattering

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Abstract

A new type of neutron-scattering spectroscopy is presented that is designed specifically to measure dynamics in bio-systems that are difficult to obtain in any other way. The temporal information is largely model-free and is analogous to relaxation processes measured with dielectric spectroscopy, but provides additional spacial and geometric aspects of the underlying dynamics. Numerical simulations of the basic instrument design show the neutron beam can be highly focussed, giving efficiency gains that enable the use of small samples. Although we concentrate on continuous neutron sources, the extension to pulsed neutron sources is proposed, both requiring minimal data-treatment and being broadly analogous with dielectric spectroscopy, they will open the study of dynamics to new areas of biophysics.

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Most cited references 27

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Role of hydration and water structure in biological and colloidal interactions.

J Israelachvili, H Wennerström (1996)

The conventional explanation of why hydrophilic surfaces and macromolecules remain well separated in water is that they experience a monotonically repulsive hydration force owing to structuring of water molecules at the surfaces. A consideration of recent experimental and theoretical results suggests an alternative interpretation in which hydration forces are either attractive or oscillatory, and where repulsions have a totally different origin. Further experiments are needed to distinguish between these possibilities.

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Dynamical transition of myoglobin revealed by inelastic neutron scattering.

W Doster, S Cusack, W Petry (1989)

Structural fluctuations in proteins on the picosecond timescale have been studied in considerable detail by theoretical methods such as molecular dynamics simulation, but there exist very few experimental data with which to test the conclusions. We have used the technique of inelastic neutron scattering to investigate atomic motion in hydrated myoglobin over the temperature range 4-350 K and on the molecular dynamics timescale 0.1-100 ps. At temperatures below 180 K myoglobin behaves as a harmonic solid, with essentially only vibrational motion. Above 180 K there is a striking dynamic transition arising from the excitation of nonvibrational motion, which we interpret as corresponding to torsional jumps between states of different energy, with a mean energy asymmetry of 12 kJ mol-1. This extra mobility is reflected in a strong temperature dependence of the mean-square atomic displacements, a phenomenon previously observed specifically for the heme iron by Mössbauer spectroscopy, but on a much slower timescale (10(-7) s). It also correlates with a glass-like transition in the hydration shell of myoglobin and with the temperature-dependence of ligand-binding rates at the heme iron, as monitored by flash photolysis. In contrast, the crystal structure of myoglobin determined down to 80 K shows no significant structural transition. The dynamical behaviour we find for myoglobin (and other globular proteins) suggests a coupling of fast local motions to slower collective motions, which is a characteristic feature of other dense glass-forming systems.

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A unified model of protein dynamics.

Keith Jansson, D. Craig Young, Paul Fenimore … (2009)

Protein functions require conformational motions. We show here that the dominant conformational motions are slaved by the hydration shell and the bulk solvent. The protein contributes the structure necessary for function. We formulate a model that is based on experiments, insights from the physics of glass-forming liquids, and the concepts of a hierarchically organized energy landscape. To explore the effect of external fluctuations on protein dynamics, we measure the fluctuations in the bulk solvent and the hydration shell with broadband dielectric spectroscopy and compare them with internal fluctuations measured with the Mössbauer effect and neutron scattering. The result is clear. Large-scale protein motions are slaved to the fluctuations in the bulk solvent. They are controlled by the solvent viscosity, and are absent in a solid environment. Internal protein motions are slaved to the beta fluctuations of the hydration shell, are controlled by hydration, and are absent in a dehydrated protein. The model quantitatively predicts the rapid increase of the mean-square displacement above approximately 200 K, shows that the external beta fluctuations determine the temperature- and time-dependence of the passage of carbon monoxide through myoglobin, and explains the nonexponential time dependence of the protein relaxation after photodissociation.

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Author and article information

Journal

Journal ID (nlm-ta): Sci Rep

Journal ID (iso-abbrev): Sci Rep

Title: Scientific Reports

Publisher: Nature Publishing Group

ISSN (Electronic): 2045-2322

Publication date (Electronic): 05 October 2016

Publication date Collection: 2016

Volume: 6

Electronic Location Identifier: 34266

Affiliations

[1 ]School of Physics, University College Dublin , Dublin, Ireland

[2 ]Laboratory for Neutron Scattering, Paul Scherrer Institut , Villigen, Switzerland

[3 ]School of Materials Science and Engineering, UNSW Australia , Sydney, NSW 2052, Australia

Author notes

[a ] antonio.benedetto@ 123456psi.ch

Article

Publisher Item ID: srep34266

DOI: 10.1038/srep34266

PMC ID: 5050422

PubMed ID: 27703184

SO-VID: 08a84588-237e-48f3-bedb-1726bd148364

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Elastic Scattering Spectroscopy (ESS): an Instrument-Concept for Dynamics of Complex (Bio-) Systems From Elastic Neutron Scattering

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Most cited references 27

Role of hydration and water structure in biological and colloidal interactions.

Dynamical transition of myoglobin revealed by inelastic neutron scattering.

A unified model of protein dynamics.

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