Page 60 - ILL Annual Report 2019

BIOLOGY AND HEALTH
During this project, M. Grimaldo, H. Lopez (TU Dublin) and F. Roosen-Runge (Malmö University) have been postdoctoral/ visiting fellows at the ILL, and C. Beck a PhD student, jointly funded by the ILL and the University of Tübingen. This research was supported by the grant ‘ImmunoglobulinCrowding’ jointly funded by the DFG and ANR.
The effect of polydispersity on protein diffusion in naturally crowded cellular environments
Backscattering spectrometer IN16B, small-angle scattering instrument D11, theory and D-Lab
The interior of living cells is marked by the presence of various macromolecules at high concentrations. Combining high-resolution neutron spectroscopy with computer simulations, the effect
of the polydispersity within such a naturally crowded environment can be quantitatively understood on nanosecond time and nanometre length scales. In a pioneering study, this approach has been established employing immunoglobulins as tracer proteins. The resulting knowledge will contribute to our understanding of intracellular transport and assembly.
AUTHORS
M. Grimaldo and T. Seydel (ILL)
H. Lopez (ILL and UGA Grenoble University, France) C. Beck (ILL and Tübingen University, Germany)
F. Roosen-Runge (Malmö University, Sweden)
F. Schreiber (Tübingen University, Germany)
ARTICLE FROM
J. Phys. Chem. Lett. (2019)—doi: 10.1021/acs.jpclett.9b00345
REFERENCES
[1] M. Grimaldo, H. Lopez, C. Beck, F. Roosen-Runge, M. Moulin,
J. Devos, V. Laux, M. Härtlein, S. Da Vela, R. Schweins, A. Mariani,
F. Zhang, J.L. Barrat, M. Oettel, V.T. Forsyth, T. Seydel and F. Schreiber, J. Phys. Chem. Lett. 10 (2019) 1709
In pursuit of predicting biological dynamics at the molecular level, physical concepts can greatly advance quantitative modelling. Notably, concepts from colloid physics can help us to understand the diffusion of biological macromolecules on the nanometre length scale commensurate with molecular dimensions. Neutrons provide an ideal probe, being able to access the short-time tracer diffusion without causing any damage to the fragile biological samples and allowing selective information via the scattering contrast without the need for any labels on the proteins.
We combined high-resolution neutron spectroscopy experiments with computer simulations on samples
closely mimicking the natural, crowded macromolecular environment but allowing for systematic control of the system parameters, such as the tracer protein and crowder concentrations (figure 1) [1]. Complementary small-angle X-ray and neutron scattering experiments helped to further characterise the samples, confirming the presence of macromolecules and assemblies with a very broad range of shapes and length scales.
Figure 1
Experimental agreement of immunoglobulin diffusion under polydisperse and monodisperse crowding.
Main figure: experimental apparent diffusion coefficient D(φ) versus the total volume fraction φ of Ig and lysate combined; grey symbols = Ig without lysate; coloured symbols = Ig–lysate mixtures. Dashed line = polynomial fit Dp(φ) of the diffusion of Ig in pure D2O.
Top inset: D(φ) versus Dp(φ) for the samples with lysate (R2w: weighted coefficient of determination). The shaded area depicts a ±5 % deviation of D(φ) from Dp(φ).
Bottom inset: artistic view of the two experimental systems (Ig–D2O, bottom left, and Ig–lysate mixture, top) and of the simulations of hard-sphere suspensions (bottom right), all demonstrating the importance of hydrodynamic interactions.
ANNUAL REPORT 2019