0021 Genetic engineering of polypeptide block copolymer that form ...


Dec 11, 2012 (4 years and 6 months ago)


Genetic engineering of polypeptide block copolymer that form large nanostructures
Ara Moses
, Vinod Valluripalli, Guoyong Sun, Siti Janib, Andrew MacKay
University of Southern California School of Pharmacy, Los Angeles, CA, USA
Block copolymers that assemble into vesicles, micelles, and worms, have potential
applications for targeted drug delivery. Similar to polar lipids, amphipathic block copolymers
have hydrophobic and hydrophilic regions that drive the assembly of nanostructures. Despite
progress with synthetic polymeric materials, there are few reports of equivalent behavior
observed for protein block copolymers. Protein polymers are genetically encoded amino acid
sequences, based on either homopolymers or repetitive motifs. Like synthetic polymers,
protein polymers have physico-chemico properties that are determined by the nature and
arrangement of their monomers. Unlike synthetic polymers, protein polymers can be
generated at high precision using recombinant DNA methodology. As gene products, protein
polymers can be fused to other biologically active proteins, which constitutes an elegant
approach to assemble biologically active peptides (antibodies, toxins, enzymes, peptide
ligands). To facilitate this approach, this study describes a rational study of protein
biopolymers that undergo controlled assembly of micelles and larger nanostructures.

A library of protein polymers was generated from elastin-like polypeptides (ELPs).
ELPs are biodegradable, repetitive polypeptides that undergo reversible assembly above a
characteristic inverse phase transition temperature. Block copolymers were designed by
joining hydrophobic (Val-Pro-Gly-Ile-Gly)
and hydrophilic (Val-Pro-Gly-Ser-Gly)
segments. A diblock copolymer that is hydrophilic 49 % by mass assembled into micelles with
a hydrodynamic diameter of 46 nm at physiological temperature. By reducing the hydrophilic
fraction to between 26 to 40 %, the resulting copolymers assemble significantly larger
structures, ranging in diameter from 100 to 2000 nm. Fluorescence microscopy revealed the
presence of vesicular lamellae for the larger structures; furthermore, these particles were
capable of encapsulating hydrophilic dyes. Similar to polymersomes and liposomes, the
diameter and polydispersity of ELP nanoparticles can be adjusted by extrusion through a
porous polycarbonate membrane. The block copolymers described here may be useful to
assemble biologically active peptides into therapeutic nanostructures.