Macromolecular diffusion in crowded media beyond the hard-sphere model

Abstract

The effect of macromolecular crowding on diffusion beyond the hard-core sphere model is studied. A new coarse-grained model is presented, the Chain Entanglement Softened Potential (CESP) model, which takes into account the macromolecular flexibility and chain entanglement. The CESP model uses a shoulder-shaped interaction potential that is implemented in the Brownian Dynamics (BD) computations. The interaction potential contains only one parameter associated with the chain entanglement energetic cost (Ur). The hydrodynamic interactions are included in the BD computations via Tokuyama mean-field equations. The model is used to analyze the diffusion of a streptavidin protein among different sized dextran obstacles. For this system, Ur is obtained by fitting the streptavidin experimental long-time diffusion coefficient Dlongversus the macromolecular concentration for D50 (indicating their molecular weight in kg mol−1) dextran obstacles. The obtained Dlong values show better quantitative agreement with experiments than those obtained with hard-core spheres. Moreover, once parametrized, the CESP model is also able to quantitatively predict Dlong and the anomalous exponent (α) for streptavidin diffusion among D10, D400 and D700 dextran obstacles. Dlong, the short-time diffusion coefficient (Dshort) and α are obtained from the BD simulations by using a new empirical expression, able to describe the full temporal evolution of the diffusion coefficient.

We acknowledge the financial support from the Spanish Ministry of Science and Innovation (project CTM2016-78798-C2-1-P) and Generalitat de Catalunya (Grants 2014SGR1017, 2014SGR1132 and XrQTC). Sergio Madurga and Francesc Mas acknowledge the funding of the EU project 8SEWP-HORIZON 2020 (692146). PabloM. Blanco also acknowledges the financial support fromthe grant (FI-2017) of Generalitat de Catalunya. The authors also want to thank Prof. Giancarlo Franzese (University of Barcelona) for his suggestion to use a shouldered interaction potential to model macromolecular flexibility.