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Synthesis of Zwitterionic Polymers Containing a Tertiary Sulfonium Group for Protein Stabilization

Imamura, Ryutaro, Mori, Hideharu
Biomacromolecules 2018 v.20 no.2 pp. 904-915
algae, alkaline phosphatase, antibodies, composite polymers, cytotoxicity, dimethylsulfoniopropionate, freeze-thaw cycles, immunoglobulin G, methyl iodide, mice, peroxidase, polymerization, storage temperature, zwitterions
The present study demonstrates the controlled synthesis and biological potential of poly(N-acryloyl-l-methionine methyl sulfonium salt)s (poly(A-Met(S⁺)–OH)s), which mimic dimethylsulfoniopropionate (DMSP), a compound produced by marine algae to protect their proteins. The novel sulfonium-containing zwitterionic polymers were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization of the amino acid-based monomer N-acryloyl-l-methionine (A-Met-OH) followed by a postmodification process in which the sulfide groups were reacted with iodomethane. The DMSP-mimic zwitterionic macromolecules were shown for the first time to exhibit low cytotoxicity and the ability to stabilize proteins. By adding the resulting poly(A-Met(S⁺)–OH)s to horse radish peroxidase (HRP) solution, the activity of HRP was maintained even after storage at 4 °C for several days. In addition, the protein activities were tested using peroxidase-labeled antibody to mouse immunoglobulin G (IgG-HRP) and alkaline phosphatase (ALP) after storage and for HRP after freeze–thaw cycles. Amphiphilic random copolymers, poly(A-Met(S⁺)–OH-co-BA)s, also exhibited excellent properties for protein stabilization.