Artificial Enzymes Combining Proteins with Proline Polymers for Asymmetric Aldol Reactions in Water

Abstract

Artificial enzymes, usually created by incorporating one or two abiological catalytic species into protein hosts, are becoming promising tools for biocatalysis. However, they are still far behind natural enzymes due to their limited active sites with low activity and selectivity. Here, we proposed a polymeric approach to generate artificial enzymes by combining proteins with organocatalytic polymers, in which multiple proline organocatalysts are grafted from protein scaffolds via atom-transfer radical polymerization. The resultant artificial polyenzymes, abbreviated as “ArPoly”, have similar physicochemical properties as natural enzymes and proved to be effective aldolase mimics for the aqueous asymmetric aldol reaction, in which an optimal ArPoly gave rise to 33% conversion and 94% enantioselectivity. Therefore, we proved the concept of water-soluble proline-based organocatalyst for aqueous asymmetric aldol reactions. This success not only expands the toolbox of asymmetric organocatalysis but also opens other avenues in the field of artificial enzymes where a plethora of proteins/enzymes can be combined with various well-designed organocatalytic polymers for synthetically useful reactions.

Copper-Containing Artificial Polyenzymes as a Clickase for Bioorthogonal Chemistry

“…For the preparation of ArPoly clickase , a synthetic water-soluble initiator, N -2-bromo-2-methylpropanoyl-β-alanine N ′-oxysuccinimide ester, was first linked to the surface lysine residues of BSA to generate BSA macro initiator (BSA MI) (Scheme S1). The linkage was confirmed by the molecular weight difference of 11,500 between native BSA (average MW 66 kDa) and BSA MI (average MW 77.5 kDa) in the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (Figure a), implying around 51 initiators in BSA MI as before . The molecular weight difference was further observed in the SDS-PAGE result showing two discrete bands with similar molecular weights corresponding to that in the MALDI-TOF (Figure b).…”

“…The linkage was confirmed by the molecular weight difference of 11,500 between native BSA (average MW 66 kDa) and BSA MI (average MW 77.5 kDa) in the matrix-assisted laser desorption/ ionization time-of-flight (MALDI-TOF) mass spectrometry (Figure 1a), implying around 51 initiators in BSA MI as before. 32 The molecular weight difference was further observed in the SDS-PAGE result showing two discrete bands with similar molecular weights corresponding to that in the MALDI-TOF (Figure 1b). The self-designed monomer, O-(2-methacryloyloxyethylsuccinoyl)-trans-4-hydroxy-L-proline, was polymerized onto BSA via copper-catalyzed "grafting-from" polymerization, serving as copper ligands, resulting in copper-containing ArPoly (ArPoly clickase ) (Scheme S2).…”

“…Beyond that, polymers were designed and applied to construct the outer coordination sphere surrounding metal clusters, acting as catalytic metallopolymers for hydrogen production . Very recently, benefiting from the in-depth understanding of structure–function relations, artificial polyenzymes (ArPoly) have been seminally proposed as a new type of artificial enzyme . Therein, a controllable number of synthetic l -proline have been incorporated into common protein scaffolds such as green fluorescent protein (GFP) as active sites.…”

“…31 Very recently, benefiting from the in-depth understanding of structure−function relations, artificial polyenzymes (ArPoly) have been seminally proposed as a new type of artificial enzyme. 32 Therein, a controllable number of synthetic L-proline have been incorporated into common protein scaffolds such as green fluorescent protein (GFP) as active sites. The obtained ArPoly were proved to be the first water-soluble aldolase mimics able to catalyze aldol reactions in water with excellent selectivity.…”

Tailoring Protein–Polymer Conjugates as Efficient Artificial Enzymes for Aqueous Asymmetric Aldol Reactions

“…5 Very recently, we have proposed a novel polymerization approach to generate protein−polymer conjugates by combining protein scaffolds with organocatalytic polymers as a new type of artificial enzyme. 19 These protein−polymer conjugates own several advantages over conventional artificial enzymes. First, the polymeric approach allows for the unitization of a variety of common protein scaffolds such as bovine serum albumin.…”