(415g) Self-Assembly of Globular Protein-Polymer Diblock Copolymers

Protein-based materials show a great deal of
potential as catalysts and optoelectronics, where the unique efficiency,
selectivity, or activity of enzymes can be captured to improve material
performance.  The self-assembly of
globular protein-polymer diblock copolymers into nanostructured phases is
demonstrated as an elegant and simple method for structural control in
protein-based biocatalysts or bioelectronics. 
In order to fundamentally investigate self-assembly in these complex
block copolymer systems, a mutant of the red fluorescent protein mCherry is expressed in E.
coli and site-specifically conjugated to a low polydispersity
poly(N-isopropyl acrylamide) (PNIPAM) block. 
Using thiol-maleimide coupling, a well-defined
model globular protein-polymer diblock copolymer is
formed.  Nanostructured protein materials
are self-assembled by the evaporation of water from concentrated solutions of
the diblock copolymer.  Through changes in the temperature of the
solution or use of volatile acids and bases, different pathways toward
self-assembly may be accessed.  Small
angle X-ray scattering and transmission electron microscopy are used to explore
the dependence of nanostructure formation on the processing pathway, and
solvent annealing was used to achieve more fully equilibrated structures.  The effect of the molecular weight of the
PNIPAM block was also investigated, demonstrating the ability to self-assemble
a variety of different nanostructured morphologies from globular proteins.  Wide angle X-ray scattering illustrates that
diblock copolymer self-assembly results in a noncrystalline
structure within the protein nanodomains. 
Circular dichroism , UV/Vis spectroscopy, and Fourier transform
infra-red (FTIR) spectroscopy show that a large fraction of the protein remains
in its folded state after conjugation, and the activity of the protein is
explored as a function of processing conditions to identify conditions that maximize
the preservation of protein function.