Simple Derivatization of RAFT-Synthesized Styrene-Maleic Anhydride Copolymers for Lipid Disk Formulations.

Styrene-maleic acid copolymers have received significant attention because of their ability to interact with lipid bilayers and form styrene-maleic acid copolymer lipid nanoparticles (SMALPs). However, these SMALPs are limited in their chemical diversity, with only phenyl and carboxylic acid functional groups, resulting in limitations because of sensitivity to low pH and high concentrations of divalent metals. To address this limitation, various nucleophiles were reacted with the anhydride unit of well-defined styrene-maleic anhydride copolymers in order to assess the potential for a new lipid disk nanoparticle-forming species. These styrene-maleic anhydride copolymer derivatives (SMADs) can form styrene-maleic acid derivative lipid nanoparticles (SMADLPs) when they interact with lipid molecules. Polymers were synthesized, purified, characterized by Fourier-transform infrared spectroscopy, gel permeation chromatography, and nuclear magnetic resonance and then used to make disk-like SMADLPs, whose sizes were measured by dynamic light scattering (DLS). The SMADs form lipid nanoparticles, observable by DLS and transmission electron microscopy, and were used to reconstitute a spin-labeled transmembrane protein, KCNE1. The polymer method reported here is facile and scalable and results in functional and robust polymers capable of forming lipid nanodisks that are stable against a wide pH range and 100 mM magnesium.

Two-distinct polymer ubiquitin conjugates by photochemical grafting-from.

Protein-polymer bioconjugates present a way to make enzymes more efficient and robust for industrial and medicinal applications. While much work has focused on mono-functional conjugates, i.e. conjugates with one type of polymer attached such as poly(ethylene glycol) or poly(N-isopropylacrylamide), there is a practical interest in gaining additional functionality by synthesizing well-defined bifunctional conjugates in a hetero-arm star copolymer architecture with protein as the core. Using ubiquitin as a model protein, a synthetic scheme was developed to attach two different polymers (OEOMA and DMAm) directly to the protein surface, using orthogonal conjugation chemistries and grafting-from by photochemical living radical polymerization techniques. The additional complexity arising from attempts to selectively modify multiple sites led to decreased polymerization performance and indicates that ICAR-ATRP and RAFT are not well-suited to bifunctional bioconjugates applications. Nonetheless, the polymerization conditions preserve the native fold of the ubiquitin and enable production of a hetero-arm star protein-polymer bioconjugate.