Soft Matter
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Thermal motion in the multi-subunit protein, apoferritin, as
probed by high energy resolution neutron spectroscopy
Mark. T. F. Telling ,* Cameron Neylon, Luke Clifton,
Spencer Howells, Lambert van Eijck
and Victoria Garc
ıa SakaiART
C1SM0560c1sm05603d3D_GRABS

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Soft MatterThermal motion in the multi-subunit p
energy resolution neutron spectroscop
Mark. T. F. Telling ,†*ab Cameron Neylon,b Luke Cli
and Victoria Garc
ıa Sakaib
Received 6th April 2011, Accepted 31st May 2011
DOI: 10.1039/c1sm05603d
Insight into the dynamic landscape of the multi-subunit globular
spectroscopy is presented in this paper. We combine elastic and q
collected using three different neutron spectrometers, to probe len
up to 2 ns. We show, for the first time without ambiguity, and via a
that in its lyophilised form, apoferritin, above T
100 K and in th
dynamic response driven by methyl groups alone. No contribution
with non-methyl species. A distribution of CH3 activation energi
environmental heterogeneity that exists around the methyl specie
performing a complete and detailed analysis of the neutron scatter
theoretical assumptions required by the methyl group activation
spectral response.
1. Introduction
It is well established that protein dynamics play a pivotal role in
biological functions such as enzyme catalysis, ligand binding and
protein folding, and thus a detailed analysis of the dynamical
landscape is required to fully appreciate the intricate relationship
between dynamics and biological function. Neutron spectros-
copy is an ideal tool with which to gain insight into the dynamics
of biomolecules1 since it not only is a non-destructive and
selective technique but also provides simultaneously spatial and
temporal information. In addition, the parameters extracted
from experimental neutron studies are directly akin to those
calculated in molecular dynamic (MD) simulations;2,3 such
interplay helping illuminate the dynamic complexity of biological
systems. The range of bio-macromolecular problems addressed
using neutron spectroscopy is considerable. For a comprehensive
overview see for example Fitter et al.4 and references therein.
However, in broad terms the neutron method has been success-
fully applied to problems that encompass proteins,5
membranes,6,7 lipids,8,9 nucleic acids10 and saccharides.11–13
aDepartment of Materials, University of Oxford, Parks, Road, Oxford,
OX1 3PH, UK. E-mail: mark.telling@materials.ox.ac.uk
bISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, OX11
OQX, UK. E-mail: victoria.garcia-sakai@stfc.ac.uk; luke.clifton@stfc.
ac.uk; spencer.howells@stfc.ac.uk; cameron.neylon@stfc.ac.uk; mark.
telling@stfc.ac.uk
cTU Delft, Postbus 5, 2600 AA Delft, The Netherlands. E-mail: l.
vaneijck@tudelft.nl
† Position held: Academic Visitor
Cite this: DOI: 10.1039/c1sm05603d
www.rsc.org/softmatterART
C1SM
This journal is ª The Royal Society of Chemistry 2011tein, apoferritin, as probed by high
n,b Spencer Howells,†b Lambert van Eijckc
tein, apoferritin, using neutron
si-elastic neutron scattering data
scales up to 10 A and timescales
orough and systematic approach,
s–ns time regime, exhibits a single
observed from protons associated
s obtained in line with the
this protein. In addition, by
data, we prove the validity of the
del used to analyse the observed
Previously, we used neutron scattering spectroscopy to char-
acterise the dynamic landscape in hydrated and lyophilised
apoferritin14 in the pico-second (ps) time regime and over length
scales of 3.5 to 9 A. Apoferritin is an intracellular iron storage
protein found in almost all living organisms, and represents
a model system for colloidal bio-systems due to its mono-
disperse spherical form factor. Considering the lyophilised
material, we observed a weak inflection in the mean squared
displacement (msd) parameter at
100 K, analogous to that
observed in other dry proteins, and the corresponding elastic
neutron scattering intensity was successfully modelled using
theory developed to describe methyl group activation processes
in glassy polymers.15 The role, contribution and importance of
methyl group motions to any measured bulk protein dynamic
response should not be understated, as stressed in 16,17.
However, in this study it was unclear whether higher energy
resolution spectroscopy, which probed dynamical processes on
a nanosecond timescale, would reveal not only CH3 dynamics
but also other possible dynamic processes at temperatures
between 100 and 300 K. In addition, certain theoretical
assumptions needed to be imposed when modelling the data,
including (i) that the relaxation rate followed an Arrhenius form
and (ii) that the elastic incoherent structure factor, Ao(Q) took
the form of the 3-fold jump rotation model.18
To truly understand the dynamic landscape in lyophilised
apoferritin, to investigate the presence of additional dynamic
processes on the nano-second timescale, and thus enhance the
experimental data available for future bio-molecular MD effort
on this protein system, we have now performed higher energy
PAPER05603D
Soft Matter, 2011, xx, 1–9 | 1