Enhancing the stability of trehalose synthase via SpyTag/SpyCatcher cyclization to improve its performance in industrial biocatalysts

Recent progress in lactate oxidase-based drug delivery systems for enhanced cancer therapy

Lactate oxidase (LOX) is a natural enzyme that efficiently consumes lactate. In the presence of oxygen, LOX can catalyse the formation of pyruvate and hydrogen peroxide (H2O2) from lactate. This process led to acidity alleviation, hypoxia, and a further increase in oxidative stress, alleviating the immunosuppressive state of the tumour microenvironment (TME). However, the high cost of LOX preparation and purification, poor stability, and systemic toxicity limited its application in tumour therapy. Therefore, the rational application of drug delivery systems can protect LOX from the organism's environment and maintain its catalytic activity. This paper reviews various LOX-based drug-carrying systems, including inorganic nanocarriers, organic nanocarriers, and inorganic-organic hybrid nanocarriers, as well as other non-nanocarriers, which have been used for tumour therapy in recent years. In addition, this area's challenges and potential for the future are highlighted.

Effect of SpyTag/SpyCatcher cyclization on stability and refolding of green fluorescent protein

To study the effect of SpyTag/SpyCatcher cyclization on stability and refolding of protein, we constructed a cyclized green fluorescent protein (SRGFP) and its derivative to act as a linear structure control (L-SRGFP). SRGFP and L-SRGFP showed similar fluorescence characteristics to the wild-type GFP, while compared with GFP and L-SRGFP, the thermal stability and denaturation resistance of SRGFP were improved. The refolding efficiencies of these three denatured proteins were investigated under different pH, temperature and initial protein concentration conditions, and it was found that SRGFP was superior to GFP and L-SRGFP in terms of refolding yield and refolding speed. In the pH range of 8.0-8.5, SRGFP could basically recover all fluorescence, while GFP and L-SRGFP recovered only about 87.52% and 88.58%. When refolded at a high temperature (37 °C), SRGFP still recovered 85.27% of the fluorescence, whereas GFP and L-SRGFP recovered only around 69.43% and 68.45%. At a high initial protein concentration (5 mg/mL), the refolding yield of SRGFP was about 15% higher than that of both GFP and L-SRGFP. These results suggest that the introduction of SpyRing structure (head-to-tail cyclization via SpyTag and SpyCatcher) improved the protein's stability and facilitated the refolding of denatured protein.

Cell-Free Biosynthesis System: Methodology and Perspective of in Vitro Efficient Platform for Pyruvate Biosynthesis and Transformation

The modification of intracellular metabolic pathways by metabolic engineering has generated many engineered strains with relatively high yields of various target products in the past few decades. However, the unpredictable accumulation of toxic products, the cell membrane barrier, and competition between the carbon flux of cell growth and product synthesis have severely retarded progress toward the industrial-scale production of many essential chemicals. On the basis of an in-depth understanding of intracellular metabolic pathways, scientists intend to explore more sustainable methods and construct a cell-free biosynthesis system in vitro. In this review, the synthesis and application of pyruvate as a platform compound is used as an example to introduce cell-free biosynthesis systems. We systematically summarize a proposed methodology workflow of cell-free biosynthesis systems, including pathway design, enzyme mining, enzyme modification, multienzyme assembly, and pathway optimization. Some new methods, such as machine learning, are also mentioned in this review.

Protein Macrocyclization for Tertiary Structure Stabilization

Proteins possess unique molecular recognition capabilities and enzymatic activities, features that are usually tied to a particular tertiary structure. To make use of proteins for biotechnological and biomedical purposes, it is often required to enforce their tertiary structure in order to ensure sufficient stability under the conditions inherent to the application of interest. The introduction of intramolecular crosslinks has proven efficient in stabilizing native protein folds. Herein, we give an overview of methods that allow the macrocyclization of expressed proteins, discussing involved reaction mechanisms and structural implications.

Cell-free Biosynthesis of Chlorogenic Acid Using a Mixture of Chassis Cell Extracts and Purified Spy-Cyclized Enzymes

A novel cell-free biosynthesis system based on a mixture of chassis cell extracts and purified Spy-cyclized enzymes (CFBS-mixture) was developed. As a demonstration, the CFBS-mixture was applied to chlorogenic acid (CGA) biosynthesis. The mix-and-match and Plackett-Burman experiments demonstrated that Lonicera japonica hydroxycinnamate-CoA quinate transferase and p-hydroxyphenylacetate 3-hydroxylase were the key enzymes for the production of CGA. After optimization of the concentrations of the biosynthetic enzymes in the CFBS-mixture reaction using the Plackett-Burman experimental design and the path of the steepest ascent, 711.26 ± 15.63 mg/L CGA was produced after 16 h, which is 71.1-fold the yield obtained using the conventional crude extract-based CFBS and 9.1-fold the reported yield obtained using the living cells. Based on the CFBS-mixture results, the production of CGA was further enhanced in engineered Escherichia coli. The CFBS-mixture strategy is highly effective and will be useful for high-level CFBS of natural products.

Improving the thermostability of trehalose synthase from Thermomonospora curvata by covalent cyclization using peptide tags and investigation of the underlying molecular mechanism

One of the most desirable properties for industrial enzymes is high thermotolerance, which can reduce the amount of biocatalyst used and lower the production cost. Aiming to improve the thermotolerance of trehalose synthase (TreS, EC 5.4.99.16) from Thermomonospora curvata, four mutants (G78D, V289L, G322A, I323L) and four cyclized TreS variants fused using different Tag/Catcher pairs (SpyTag-TreS-SpyCatcher, SpyTag-TreS-KTag, SnoopTag-TreS-SnoopCatcher, SnoopTagJR-TreS-DogTag) were constructed. The results showed that cyclization led to a much larger increase of thermostability than that achieved via site-directed mutagenesis. The t_1/2 of all four cyclized TreS variants at 55 °C increased 2- to 3- fold, while the analysis of kinetic and thermodynamic stability indicated that the T₅₀ of the different cyclized TreS variants increased by between 7.5 °C and 15.5 °C. Molecular dynamics simulations showed that the Rg values of cyclized TreS decreased significantly, indicating that the protein maintained a tight tertiary structure at high temperatures, avoiding exposure of the hydrophobic core to the solvent. Cyclization using a Tag/Catcher pair is a simple and effective method for improving the thermotolerance of enzymes.

Exploitation of carbohydrate processing enzymes in biocatalysis

Exploitation of enzymes in biocatalytic processes provides scope both in the synthesis and degradation of molecules. Enzymes have power not only in their catalytic efficiency, but their chemoselectivity, regioselectivity, and stereoselectivity means the reactions they catalyze are precise and reproducible. Focusing on carbohydrate processing enzymes, this review covers advances in biocatalysis involving carbohydrates over the last 2-3 years. Given the notorious difficulties in the chemical synthesis of carbohydrates, the use of enzymes for synthesis has potential for significant impact in the future. The use of catabolic enzymes in the degradation of biomass, which can be exploited in the production of biofuels to provide a sustainable and greener source of energy, and the synthesis of molecules that have a range of applications including in the pharmaceutical and food industries will be explored.

Developing a Protein Scaffolding System for Rapid Enzyme Immobilization and Optimization of Enzyme Functions for Biocatalysis

Immobilization of enzymes is required for most biocatalytic processes, but chemistries used in enzyme immobilization are limited and can be challenging. Genetically encoded protein-based biomaterials could provide easy-to-use immobilization platforms for biocatalysts. We recently developed a self-assembling protein scaffold that covalently immobilized SpyTagged enzymes by engineering the bacterial microcompartment protein EutM from Salmonella enterica with a SpyCatcher domain. We also identified a range of EutM homologues as robust protein nanostructures with diverse architectures and electrostatic surface properties. In this work, we created a modular immobilization platform with tunable surface properties by developing a toolbox of self-assembling, robust EutM-SpyCatcher scaffolds. Using an alcohol dehydrogenase as model biocatalyst, we show that the scaffolds improve enzyme activity and stability. This work provides a modular, easy-to-use immobilization system that can be tailored for the optimal function of biocatalysts of interest.