TRANSLATIONAL AND ROTATIONAL DIFFUSION OF GLOBULAR PROTEINS IN CONCENTRATED POLYMER NETWORKS

Abstract

The dynamics of a model ovalbumin protein in a dense polymer mesh, including both translational diffusion and rotational diffusion, are studied by NMR. Protein dynamics in complex matrices arises in applications involving enzymatic activity in inter‐cellular compartments or in industrial enzymatic hydrolysis reactions on polysaccharides at high substrate concentrations. For enzymatic reactions translational diffusion controls the spatial extent of degradation and rotational diffusion correlates with local enzyme docking on the polymer substrate. CF₃ tagging of proteins enables the differentiation of the protein from polymer matrix. ¹⁹F pulsed field gradient NMR is used to measure translational diffusion coefficient, while T₁ and T₂ relaxation of the ¹⁹F signal is measured to obtain the rotational diffusion coefficient. Both translational and rotational diffusions are compared with micro‐mechanical hydrodynamic theories. The Brinkman effective medium model captures the reduction in both translational and rotational diffusion using the polymer correlation length determined from scaling theory as the Brinkman hydrodynamic screening length. A scaling approach correlates the reduced diffusion coefficient to the ratio of protein size to mesh size of the polymer network. In highly concentrated polymer networks, the translational diffusion of proteins is greatly hindered but the rotational mobility is much less hindered. The two correlation times are correlated in a stretched exponential form.

Keywords:

• Confined diffusion
• Effective medium theory
• Pulsed Field Gradient NMR
• Rotational diffusion
• T₁ and T₂ relaxation
• Translational diffusion