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Smart Polymer Enhanced Protein Refolding: Molecular Dynamic Simulation and Experimental Validation

Diannan Lu1, Zheng Liu1, and Jianzhong Wu2. (1) Chemical Engineering, Tsinghua University, Beijing, China, (2) Chemical Engineering, University of California, Riverside, 3637 Canyon Crest Drive, Mailbox #516, Riverside, CA 92507

Adding chemical additives, such as surfactants and polymers of appropriate hydrophobicity and concentration into the refolding buffer, often significantly enhance protein refolding, the formation of the correct tertiary structure from denatured form. Monte Carlo simulations of a two-dimensional simple lattice protein shown that polymers of suitable hydrophobicity and concentration can enhance protein refolding via enriching folding pathways to facilitate the conformational transitions. The present work aimed at gain a molecular detail of folding kinetics, using a GĻ-like off-lattice model to investigate the refolding of an all b-barrel protein via Langevin molecular dynamics. It is shown that the folding of model protein can be divided into two consecutive steps: collapsing and rearranging. While collapsing can be accelerated by polymers of strong hydrophobicity or high concentration, which also simultaneously inhibits protein aggregation due to intermolecular hydrophobic interaction, rearranging requests the dissociation of protein-polymer complex. On the other hand, long chain polymer entangles around partially folded state protein while short chain polymer penetrates into the core structure of protein, both leading to the failure of the formation of the hydrophobic core of the protein. These simulations gave a molecular insight of the experimental results published elsewhere and inspired us to develop a new folding process, i.e., using SMART polymer of adjustable hydrophobicity to meet the demands of both collapsing and rearranging. Thus a refolding process featured by a controlled temperature declining was developed and applied to refold lysozyme and CAB using Dextran-g-PNIPAAm as the SMART polymer. A significantly improved recovery of enzyme activity was obtained for these two proteins when the refolding was performed in their respective optimal temperature gradient, as predicted by the molecular simulation.