Solid-State Nanostructured Materials from Self-Assembly of a Globular Protein–Polymer Diblock Copolymer

Abstract

Self-assembly of three-dimensional solid-state nanostructures containing approximately 33% by weight globular protein is demonstrated using a globular protein-polymer diblock copolymer, providing a route to direct nanopatterning of proteins for use in bioelectronic and biocatalytic materials. A mutant red fluorescent protein, mCherryS131C, was prepared by incorporation of a unique cysteine residue and site-specifically conjugated to end-functionalized poly(N-isopropylacrylamide) through thiol-maleimide coupling to form a well-defined model protein-polymer block copolymer. The block copolymer was self-assembled into bulk nanostructures by solvent evaporation from concentrated solutions. Small-angle X-ray scattering and transmission electron microscopy illustrated the formation of highly disordered lamellae or hexagonally perforated lamellae depending upon the selectivity of the solvent during evaporation. Solvent annealing of bulk samples resulted in a transition towards lamellar nanostructures with mCherry packed in a bilayer configuration and a large improvement in long range ordering. Wide-angle X-ray scattering indicated that mCherry did not crystallize within the block copolymer nanodomains and that the β-sheet spacing was not affected by self-assembly. Circular dichroism showed no change in protein secondary structure after self-assembly, while UV-vis spectroscopy indicated approximately 35% of the chromophore remained optically active.

Rational design of nanomaterials from assembly and reconfigurability of polymer-tethered nanoparticles

“…Protein-polymer conjugates, for example, were created using a covalent binding maleimide-thiol coupling reaction to create bioconjugates. [33][34][35] These bioconjugates were also been used in self-assembly experiments, demonstrating the same phase diversity as related building blocks. [35] Other materials, such as polyoxometalate anionic metal-oxygen nanocages, have been successfully attached to polymer tethers via covalent bonds.…”

Polymer Directed Protein Assemblies

“…Olsen and coworkers used an engineered red fluorescent protein, mCherry, which was modified to contain one exposed cysteine residue making a thiol-functionality available for covalent attachment of a single polymer. Onto the thiol, a pre-synthesized poly-NIPAAm chain was attached which has on one end a maleimide-functionality which is able to conjugate to a thiol-group under mild conditions [47]. The use of pNIPAAm is a clever choice since it allows for water to be used as a non-selective as well as a selective solvent, which is normally a way to influence assembly behavior in block-copolymer films.…”

Protein nanorings organized by poly(styrene-block-ethylene oxide) self-assembled thin films

“…6,7,[9][10][11][12][13][14] Peptides or proteins have also been used as one block of block copolymers and shown to self-assemble into ordered structures. [15][16][17][18][19] Biomolecules are generally believed to be good candidates for nanotechnology due to their versatility, small size and precise control over self-assembly. In the context of block copolymers, incorporation of biomolecules heralds a new domain of novel functional materials.…”