Well-defined polymer–protein bioconjugates are widely used in therapeutics and biocatalysis. One of the challenges in the synthesis of bioconjugates is the efficient separation of the target conjugate molecules from reaction systems. In this research, surface coassembly of polymer brushes and polymer–protein bioconjugates is investigated, and it is demonstrated that the coassembly approach can be applied in the purification of polymer–protein bioconjugates. Bovine serum albumin-poly(N-isopropylacrylamide) (BSA-PNIPAM) bioconjugates were synthesized by the “grafting from” approach, and PNIPAM brushes on silica particles were prepared by the “grafting to” approach. PNIPAM brushes on silica particles are able to coassemble with BSA-PNIPAM at a temperature above the lower critical solution temperature of PNIPAM. Two-layer surface structures with collapsed PNIPAM in the inner layers and BSA in the outer layers are formed on the silica particles. The size of the silica particles and molecular weight of PNIPAM on the bioconjugates exert influences on the coassembly. The coassembly approach can be used in the purification of bioconjugates. After repeated coassembly centrifugation-release cycles, all the BSA-PNIPAM bioconjugates can be removed from the reaction solutions, and the purified bioconjugates are obtained.
Self-assembly of proteins into well-organized proteinosomes has attracted great interest due to the potential medical and biological applications of the structures. Herein, a new concept of electrostatic assisted fabrication of proteinosomes is proposed. The self-assembly is performed by using multi-step dialysis approach, where negatively charged bovine serum albumin-poly( N -isopropylacrylamide) (BSA-PNIPAM) bioconjugate and positively charged enzyme (lysozyme or trypsin) are initially dissolved in phosphate buffer (PB) solution at a high salt concentration, and subsequently the protein solution is dialyzed against PB solutions at low salt concentrations, resulting in the formation of biofunctional proteinosomes. Transmission electron microscopy (TEM), cryo-TEM and light scattering results all demonstrate the formation of hollow structures. The wall of a proteinosome is composed of BSA and enzyme (lysozyme or trypsin), and PNIPAM chains of the bioconjugate are in the corona stabilizing the structure. In comparison with the native enzymes, the enzyme molecules in the assemblies basically retain their bioactivities. The proteinosomes formed by BSA-PNIPAM and lysozyme can be dissociated in the presence of trypsin, and those self-assembled by BSA-PNIPAM and trypsin are able to be self-hydrolyzed, resulting in the dissociation of the structures in aqueous solution. The size and morphology changes of the proteinosomes in the hydrolysis are studied.
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