Poly(ethylene glycol)-Supported Enzyme Inactivators. Efficient Identification of the Site of Covalent Attachment to α-Chymotrypsin by PEG-TPCK

Creation of an artificial metalloprotein with a Hoveyda-Grubbs catalyst moiety through the intrinsic inhibition mechanism of α-chymotrypsin

An L-phenylalanyl chloromethylketone-based inhibitor equipped with a Hoveyda-Grubbs catalyst moiety was regioselectively incorporated into the cleft of α-chymotrypsin through the intrinsic inhibition mechanism of the protein to construct an artificial organometallic protein.

Thermoresponsive block copolymer-protein conjugates prepared by grafting-from via RAFT polymerization

Well-defined "smart" block copolymer-protein conjugates were prepared by two consecutive "grafting-from" reactions via reversible addition-fragmentation chain transfer (RAFT) polymerization. The initiating portion (R-group) of the RAFT agent was anchored to a model protein such that the thiocarbonylthio moiety was readily accessible for chain transfer with propagating chains in solution. Well-defined polymer-protein conjugates of poly(N-isopropylacrylamide) (PNIPAM) and bovine serum albumin (BSA) were prepared at room temperature in aqueous media. The retained trithiocarbonate moiety on the free end group of the immobilized polymer allowed the homopolymer conjugate to be extended by polymerization of N,N-dimethylacrylamide. Polyacrylamide gel electrophoresis, size exclusion chromatography, and NMR spectroscopy confirmed the synthesis of the various conjugates and revealed that the polymerizations were well controlled. As expected, the resulting block copolymer-protein conjugates demonstrated thermoresponsive behavior due to the temperature-sensitivity of the PNIPAM block, as evidenced by turbidity measurements and dynamic light scattering analysis.

Modulation of enzyme-substrate selectivity using tetraethylene glycol functionalized gold nanoparticles

Tetraethylene glycol (TEG) functionalized gold nanoparticles with 2 nm core diameters (AuTEG) enhance alpha-chymotrypsin (ChT) enzyme activity in a substrate-selective fashion. We explored the hydrolysis of four different substrates and observed a marked increase in activity with the most hydrophobic substrate N-succinyl-alanine-alanine-proline-phenylalanine- p-nitroanilide (TP), while the other substrates remain virtually unaffected by the AuTEG 'crowding effect' in solution. The enhancement in catalysis is indicated by an increase in K(cat)/K(m) as obtained from Lineweaver-Burk analysis and we hypothesize it to arise from a macromolecular crowding effect analogous to that observed with high molecular weight poly(ethylene glycol) (PEG) polymers.

In Situ Preparation of Protein−“Smart” Polymer Conjugates with Retention of Bioactivity

Protein-polymer conjugates are widely used in biotechnology and medicine, and new methods to prepare the bioconjugates would be advantageous for these applications. In this report, we demonstrate that bioactive "smart" polymer conjugates can be synthesized by polymerizing from defined initiation sites on proteins, thus preparing the polymer conjugates in situ. In particular, free cysteines, Cys-34 of bovine serum albumin (BSA) and Cys-131 of T4 lysozyme V131C, were modified with initiators for atom transfer radical polymerization (ATRP) either through a reversible disulfide linkage or irreversible bond by reaction with pyridyl disulfide- and maleimide-functionalized initiators, respectively. Initiator conjugation was verified by electrospray-ionization mass spectroscopy (ESI-MS), and the location of the modification was confirmed by muLC-MSMS (tandem mass spectrometry) analysis of the trypsin-digested protein macroinitiators. Polymerization of N-isopropylacrylamide (NIPAAm) from the protein macroinitiators resulted in thermosensitive BSA-polyNIPAAm and lysozyme-polyNIPAAm in greater than 65% yield. The resultant conjugates were characterized by gel electrophoresis and size exclusion chromatography (SEC) and easily purified by preparative SEC. The identity of polymer isolated from the BSA conjugate was confirmed by (1)H NMR, and the polydispersity index was determined by gel permeation chromatography (GPC) to be as low as 1.34. Lytic activities of the lysozyme conjugates were determined by two standard assays and compared to that of the unmodified enzyme prior to polymerization; no statistical differences in bioactivity were observed.