Well-defined protein–polymer conjugates—synthesis and potential applications

Precisely defined protein-polymer conjugates: construction of synthetic DNA binding domains on proteins by using multivalent dendrons

Nature has evolved proteins and enzymes to carry out a wide range of sophisticated tasks. Proteins modified with functional polymers possess many desirable physical and chemical properties and have applications in nanobiotechnology. Here we describe multivalent Newkome-type polyamine dendrons that function as synthetic DNA binding domains, which can be conjugated with proteins. These polyamine dendrons employ naturally occurring spermine surface groups to bind DNA with high affinity and are attached onto protein surfaces in a site-specific manner to yield well-defined one-to-one protein-polymer conjugates, where the number of dendrons and their attachment site on the protein surface are precisely known. This precise structure is achieved by using N-maleimido-core dendrons that selectively react via 1,4-conjugate addition with a single free thiol group on the protein surface--either Cys-34 of bovine serum albumin (BSA) or a genetically engineered cysteine mutant of Class II hydrophobin (HFBI). This reaction can be conducted in mild aqueous solutions (pH 7.2-7.4) and at ambient temperature, resulting in BSA- and HFBI-dendron conjugates. The protein-dendron conjugates constitute a specific biosynthetic diblock copolymer and bind DNA with high affinity, as shown by ethidium bromide displacement assay. Importantly, even the low-molecular-weight first-generation polyamine dendron (1 kDa) can bind a large BSA protein (66.4 kDa) to DNA with relatively good affinity. Preliminary gene transfection, cytotoxicity, and self-assembly studies establish the relevance of this methodology for in vitro applications, such as gene therapy and surface patterning. These results encourage further developments in protein-dendron block copolymer-like conjugates and will allow the advance of functional biomimetic nanoscale materials.

Well-Defined Protein−Polymer Conjugates via in Situ RAFT Polymerization

Biotechnology, biomedicine, and nanotechnology applications would benefit from methods generating well-defined, monodisperse protein-polymer conjugates, avoiding time-consuming and difficult purification steps. Herein, we report the in situ synthesis of protein-polymer conjugates via reversible addition-fragmentation chain transfer polymerization (RAFT) as an efficient method to generate well-defined, homogeneous protein-polymer conjugates in one step, eliminating major postpolymerization purification steps. A water soluble RAFT agent was conjugated to a model protein, bovine serum albumin (BSA), via its free thiol group at Cys-34 residue. The conjugation of the RAFT agent to BSA was confirmed by UV-visible spectroscopy, matrix-assisted laser desorption ionization--time of flight (MALDI-TOF), and 1H NMR. BSA-macroRAFT agent was then used to control the polymerization of two different water soluble monomers, N-isopropylacrylamide (NIPAAm) and hydroxyethyl acrylate (HEA), in aqueous medium at 25 degrees C. The growth of the polymer chains from BSA-macroRAFT agent was characterized by size exclusion chromatography (SEC), 1H NMR, MALDI-TOF, and polyacrylamide gel electrophoresis (PAGE) analyses. The controlled character of the RAFT polymerizations was confirmed by the linear evolution of molecular weight with monomer conversion. The SEC analyses showed no detectable free, nonconjugated polymer formation during the in situ polymerization. The efficiency of BSA-macroRAFT agent to generate BSA-polymer conjugates was found to be ca. 1 by deconvolution of the SEC traces of the polymerization mixtures. The structural integrity and the conformation-related esterase activity of BSA were found to be unaffected by the polymerization conditions and the conjugation of the polymer chain. BSA-poly(NIPAAm) conjugates showed hybrid temperature-dependent phase separation and aggregation behavior. The lower critical solution temperature values of the conjugates were found to increase with the decrease in molecular weight of poly(NIPAAm) block conjugated to BSA.

Photoinduced reduction of catalytically and biologically active Ru(ii)bisterpyridine–cytochrome c bioconjugates

Ruthenium(II)bisterpyridine chromophores were covalently linked to iso-1 cytochrome c from yeast to create light-activated donor-acceptor bioconjugates.