Biomimetic Cellulosomes Assembled on Molecular Brush Scaffolds: Random Complexes vs Enzyme Mixtures
Journal: ACS Appl. Polym. Mater.
Date: March 16, 2021
- molecular brush
- biomimetic cellulosome
- polymer−enzyme conjugate
- biocatalytic synergism
- molecular dynamic simulations
This work reports on the development of biomimetic polymeric cellulosomes—enzyme–polymer conjugates (EPCs) generated by covalent binding of cellulase enzymes onto a molecular brush polymer scaffold synthesized by radical copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and glycidyl methacrylate (GMA). In contrast to natural cellulosomes, the EPC is generated in a random process of the conjugation of different cellulases from their mixture in the solution. The catalytic activity of the EPCs is systematically studied using carboxymethyl cellulose, microcrystalline cellulose, filter paper, and pretreated switchgrass biomass substrates. EPCs exhibit improved catalytic activity with both soluble and insoluble substrates. The synergistic effect is essential, with multifold improvement in substrate surface coverage by the enzyme being less than 50% of the saturation amount. Coarse-grained molecular dynamics simulations provide evidence for the increased concentration of EPC-delivered synergistic motifs of enzymes on the substrate as compared to the number of such motifs randomly formed by adsorption of enzymes from a mixture of free enzymes, which is in good agreement with the experiments. The catalytic activity of the EPC conjugates increases with the increased diversity of enzymes included in the EPC structure and also in the presence of free enzymes in solutions. The experiments reveal that EPCs reduce the inhibitory effect of the depolymerization product (glucose), which could facilitate higher hydrolysis rates at increased solid loadings. The experimental results demonstrate that at a random arrangement of the enzymes in the complex, the synergistic effect is substantial and comparable to that of natural cellulosomes at a low enzyme-to-substrate surface ratio due to the combination of complementary catalytic functions bound to the same EPC in close vicinity.