Speaker
Description
Proteins are complex molecular systems whose internal dynamics is
characterized by a vast spectrum of time scales, ranging from
sub-picoseconds for vibrations of chemical bonds to seconds and beyond
for large conformational rearrangements. Using a "minimalistic"
multi-time scale model for the relaxation dynamics of
proteins~[1,2], we show here that even small changes due to external stress, such as temperature, solvent modification or ligand binding,
can be elucidated by quasi-elastic neutron scattering (QENS).
The neutron intermediate scattering function is here written in the form $F(q,t)=EISF(q)+(1-EISF(q))\phi(q,t)$, where $EISF(q)$ is the elastic incoherent structure factor which gives information about the motional amplitudes of the hydrogen-atoms in hydrogen-rich systems,
and $\phi(q,t)$ is a relaxation function which is chosen to be
the "stretched" Mittag-Leffler function, $\phi(q,t)=E_\alpha(-(t/\tau)^\alpha)$ in order to account
for the asymptotically self-similar relaxation dynamics of proteins.
An important technical point is the estimation of the EISF
on the basis of its measured counterpart and the model
parameters
of the relaxation function, which are the $q$-dependent
form parameter $\alpha $ and the time scale parameter $\tau$ [3].
Our first example concerns the intrinsically disordered protein
Myelin Basic Protein (MBP) in solution, which is studied
in pure D$_2$O-buffer and in a mixture of D$_2$O-buffer with
30\%\, deuterated Trifluoroethanol at different temperatures,
in order to evaluate the impact of formation of secondary structure
elements on the internal dynamics [4]. The second example concerns
the change of the internal dynamics of myoglobin in solution
in presence of denaturing agents, and the third example
is devoted to understanding the functional dynamics
of the enzyme Phosphoglycerate kinase. Here the model allows
for determining unambiguously the amplitude of the
inter-domain fluctuations which are important for its catalytic function.
References:
[1] G. R. Kneller. PNAS USA, vol. 115, no. 38, pp. 9450-9455, 2018
[2] M. Saouessi, J. Peters, and G. R. Kneller. J. Chem. Phys.,
vol. 150, p. 161104, 2019.
[3] A. N. Hassani, A. M. Stadler, and G. R. Kneller. J. Chem. Phys.
vol. 157, p. 134103, 2022.
[4] A. N. Hassani, L. Haris, M. Appel, T. Seydel, A. M. Stadler,
and G. R. Kneller. J. Chem. Phys. vol. 156, p. 025102, 2022.
