Nanoarmoring of Proteins by Conjugation to Block Copolymer Micelles

The creation of polymer nanoparticles with protein functionality is of great interest to many applications such as targeted drug or gene delivery, diagnostic imaging, cancer theranostics, delivery of protein therapeutics, sensing chemical and biomolecular analytes in complex environments, and design of protective clothing resembling a second skin. Many approaches to achieving this goal are being explored in the current literature. In this chapter, we describe a relatively simple and flexible approach of conjugating the protein to an amphiphilic block copolymer and creating polymer nanoparticles with protein functionality by taking advantage of the intrinsic self-assembly behavior of the amphiphilic block copolymer. The commercially available and biocompatible polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is used as the polymer building block. For demonstrative purposes, bovine serum albumin was chosen as the protein. We determine the molecular weight of the protein-polymer conjugate and thereby the degree of conjugation using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry measurements. Retention of protein secondary structure in the conjugate was determined by circular dichroism spectroscopy, and the biological activity of the protein in the conjugated state has been evaluated by kinetic assay involving hydrolysis of an organophosphate compound. Dynamic light scattering and zeta potential measurements were used to characterize the size and charge of the protein-polymer conjugate micelle. Precise control of the size of the micelle and surface number density of the proteins on the micelle surface by coassembling with a second block copolymer have been demonstrated. These studies document a rational approach to armor the protein by conjugation with a block copolymer micelle, as a general approach.