Bioconjugation and Active Site Design of Enzymes Using Non-natural Amino Acids

Nature Inspired Multienzyme Immobilization: Strategies and Concepts

In a biological system, the spatiotemporal arrangement of enzymes in a dense cellular milieu, subcellular compartments, membrane-associated enzyme complexes on cell surfaces, scaffold-organized proteins, protein clusters, and modular enzymes have presented many paradigms for possible multienzyme immobilization designs that were adapted artificially. In metabolic channeling, the catalytic sites of participating enzymes are close enough to channelize the transient compound, creating a high local concentration of the metabolite and minimizing the interference of a competing pathway for the same precursor. Over the years, these phenomena had motivated researchers to make their immobilization approach naturally realistic by generating multienzyme fusion, cluster formation via affinity domain-ligand binding, cross-linking, conjugation on/in the biomolecular scaffold of the protein and nucleic acids, and self-assembly of amphiphilic molecules. This review begins with the discussion of substrate channeling strategies and recent empirical efforts to build it synthetically. After that, an elaborate discussion covering prevalent concepts related to the enhancement of immobilized enzymes' catalytic performance is presented. Further, the central part of the review summarizes the progress in nature motivated multienzyme assembly over the past decade. In this section, special attention has been rendered by classifying the nature-inspired strategies into three main categories: (i) multienzyme/domain complex mimic (scaffold-free), (ii) immobilization on the biomolecular scaffold, and (iii) compartmentalization. In particular, a detailed overview is correlated to the natural counterpart with advances made in the field. We have then discussed the beneficial account of coassembly of multienzymes and provided a synopsis of the essential parameters in the rational coimmobilization design.

Product-oriented chemical surface modification of a levansucrase (SacB) via an ene-type reaction

Carbohydrate processing enzymes are sophisticated tools of living systems that have evolved to execute specific reactions on sugars. Here we present for the first time the site-selective chemical modification of exposed tyrosine residues in SacB, a levansucrase from Bacillus megaterium (Bm-LS) for enzyme engineering purposes via an ene-type reaction. Bm-LS is unable to sustain the synthesis of high molecular weight (HMW) levan (a fructose polymer) due to protein-oligosaccharide dissociation events occurring at an early stage during polymer elongation. We switched the catalyst from levan-like oligosaccharide synthesis to the efficient production of a HMW fructan polymer through the covalent addition of a flexible chemical side-chain that fluctuates over the central binding cavity of the enzyme preventing premature oligosaccharide disengagement.

Synthesis of α-(4-Oxazolyl)amino Esters via Brønsted Acid Catalyzed Tandem Reaction

A one-step, Brønsted acid catalyzed tandem reaction for the synthesis of α-(4-oxazolyl)amino esters was developed. 4-Nitrobenzenesulfonic acid was found to be an efficient catalyst for the coupling of ethyl 2-oxobut-3-ynoates with amides to provide various α-(4-oxazolyl)amino esters. The experimental and X-ray crystallographic data suggest that a series of bond-forming reactions including imine formation, intermolecular Michael addition, and intramolecular Michael addition are involved to generate both the oxazole and amino acid functionalities.

Click reaction-aided enzymatic kinetic resolution of secondary alcohols

A new, efficient lipase-mediated kinetic resolution–click-reaction-based procedure is presented for the production of both enantiomers of various 1-(hetero)aromatic ethanols.