MOF-Immobilized Two-in-One Engineered Enzymes Enhancing Activity of Biocatalytic Cascade for Tumor Therapy

Biocatalytic systems based on enzyme cascade reactions have attracted growing interest in the field of biocatalytic medicine. However, it is a major challenge to reasonably construct enzyme cascade reactions with high stability, selectivity, and catalytic efficiency for the in vivo biocatalytic application. Herein, two-in-one engineered glucose oxidase (GOx-Fe⁰ ) is fabricated by a biomineralization strategy, through which a nanozyme (Fe⁰ NP) is anchored within the inner cavity of GOx. Then, GOx-Fe⁰ is immobilized in a pH-sensitive metal-organic framework (MOF) zeolitic imidazolate framework-8 (ZIF-8) to establish a stable and effective MOF-immobilized two-in-one engineered enzyme, GOx-Fe⁰ @ZIF-8. In vitro studies show that GOx-Fe⁰ @ZIF-8 exhibits excellent stability and high pH/glucose selectivity, and the shorter spacing between cascade enzymes can increase the cascade throughput and effectively improve the reaction efficiency of the enzyme cascade. In vivo experiments exhibit that GOx-Fe⁰ @ZIF-8 solves the instability and systemic toxicity of free enzymes, and achieves deep tumor penetration and significant chemodynamic therapeutic efficacy through a pH/glucose-selective enzyme cascade reaction in tumor site. Taken together, such an orchestrated enzyme engineering strategy can effectively improve enzyme stability, selectivity, and enzyme cascade reaction efficiency via chemical transformations, and also provide a promising strategy for the application of biocatalytic cascade reactions in vivo.

Enhanced electrochemical oxidation of ethanol using a hybrid catalyst cascade architecture containing pyrene-TEMPO, oxalate decarboxylase and carboxylated multi-walled carbon nanotube

The work presented herein demonstrates a hybrid bi-catalytic architecture for the complete electrochemical oxidation of ethanol. The new catalytic system contains pyrene-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidinyl-N-oxyl) immobilized on the surface of carboxylated multi-walled carbon nanotubes (MWCNT-COOH), and oxalate decarboxylase enzyme (OxDc) immobilized onto a carbon cloth electrode. Electrolysis revealed a stable amperometric curve and an excellent current density value over a duration of 10 h. In addition, the hybrid system immobilized on the carbon electrode exhibits outstanding stability after electrolysis. Nuclear magnetic resonance (NMR) and gas chromatography (GC) demonstrate that the hybrid electrode system is able to oxidize ethanol to CO₂ after 10 h of electrolysis. Overall, this study illustrates the enhancement of an enzymatic biofuel cell through the hybrid multi-catalytic systems, which exhibit high oxidation rates for all substrates involved in complete ethanol oxidation, enabling the collection of up to 12 electrons per molecule of ethanol.

Bioinspired architecture of a hybrid bifunctional enzymatic/organic electrocatalyst for complete ethanol oxidation

Electrochemical ethanol oxidation was performed at an innovative hybrid architecture electrode containing TEMPO-modified linear poly(ethylenimine) (LPEI) and oxalate oxidase (OxOx) immobilized on carboxylated multi-walled carbon nanotubes (MWCNT-COOH). On the basis of chromatographic results, the catalytic hybrid electrode system completely oxidized ethanol to CO₂ after 12 h of electrolysis. The fact that the developed system can catalyze ethanol electrooxidation at a carbon electrode confirms that organic oxidation catalysts combined with enzymatic catalysts allow up to 12 electrons to be collected per fuel molecule. The Faradaic efficiency of the hybrid system investigated herein lies above 87%. The combination of OxOx with TEMPO-LPEI to obtain a novel hybrid anode to oxidize ethanol to carbon dioxide constitutes a simple methodology with useful application in the development of enzymatic biofuel cells.

Engineering enzyme microenvironments for enhanced biocatalysis

Protein engineering provides a means to alter protein structure leading to new functions. Much work has focused on the engineering of enzyme active sites to enhance catalytic activity, however there is an increasing trend towards engineering other aspects of biocatalysts as these efforts can also lead to useful improvements. This tutorial discusses recent advances in engineering an enzyme's local chemical and physical environment, with the goal of enhancing enzyme reaction kinetics, substrate selectivity, and activity in harsh conditions (e.g., low or high pH). By introducing stimuli-responsiveness to these enzyme modifications, dynamic control of activity also becomes possible. These new biomolecular and protein engineering techniques are separate and independent from traditional active site engineering and can therefore be applied synergistically to create new biocatalyst technologies with novel functions.