Enhanced thermal stability of lichenase from Bacillus subtilis 168 by SpyTag/SpyCatcher-mediated spontaneous cyclization

Enhancing the stress resistance of nitrile hydratase from Rhodococcus ruber via SpyTag/SpyCatcher-mediated α- and β- subunits ligation

BACKGROUND

Nitrile Hydratase (NHase) is one of the most important industrial enzyme widely used in the petroleum exploitation field. The enzyme, composed of two unrelated α- and β-subunits, catalyzes the conversion of acrylonitrile to acrylamide, releasing a significant amount of heat and generating the organic solvent product, acrylamide. Both the heat and acrylamide solvent have an impact on the structural stability of NHase and its catalytic activity. Therefore, enhancing the stress resistance of NHase to toxic substances is meaningful for the petroleum industry.

METHODS AND RESULTS

To improve the thermo-stability and acrylamide tolerance of NHase, the two subunits were fused in vivo using SpyTag and SpyCatcher, which were attached to the termini of each subunit in various combinations. Analysis of the engineered strains showed that the C-terminus of β-NHase is a better fusion site than the N-terminus, while the C-terminus of α-NHase is the most suitable site for fusion with a larger protein. Fusion of SpyTag and SpyCatcher to the C-terminus of β-NHase and α-NHase, respectively, led to improved acrylamide tolerance and a slight enhancement in the thermo-stability of one of the engineered strains, NBSt.

CONCLUSION

These results indicate that in vivo ligation of different subunits using SpyTag/SpyCatcher is a valuable strategy for enhancing subunit interaction and improving stress tolerance.

Expression and biochemical characterization of a novel thermostable alkaline β-1,3-1,4-glucanase (lichenase) from an alkaliphilic Bacillus lehensis G1

New thermostable β-1,3-1,4-glucanase (lichenase) designated as Blg29 was expressed and purified from a locally isolated alkaliphilic bacteria Bacillus lehensis G1. The genome sequence of B. lehensis predicted an open reading frame of Blg29 with a deduced of 249 amino acids and a molecular weight of 28.99 kDa. The gene encoding for Blg29 was successfully amplified via PCR and subsequently expressed as a recombinant protein using the E. coli expression system. Recombinant Blg29 was produced as a soluble form and further purified via immobilized metal ion affinity chromatography (IMAC). Based on biochemical characterization, recombinant Blg29 showed optimal activity at pH9 and temperature 60 °C respectively. This enzyme was stable for more than 2 h, incubated at 50 °C, and could withstand ∼50 % of its activity at 70 °C for an hour and a half. No significant effect on Blg29 was observed when incubated with metal ions except for a small increase with ion Ca2+. Blg29 showed high substrate activity towards lichenan where Vm, Km, Kcat, and kcat/Km values were 2040.82 μmolmin‾1mg‾1, 4.69 mg/mL, and 986.39 s‾1 and 210.32 mLs‾1mg‾1 respectively. The high thermostability and activity make this enzyme useable for a broad prospect in industry applications.

Enhancing Poly-γ-glutamic Acid Production in Bacillus tequilensis BL01 through a Multienzyme Assembly Strategy and Expression Features of Glutamate Synthesis from Corynebacterium glutamicum

The enhancement of intracellular glutamate synthesis in glutamate-independent poly-γ-glutamic acid (γ-PGA)-producing strains is an essential strategy for improving γ-PGA production. Bacillus tequilensis BL01ΔpgdSΔggtΔsucAΔgudB:P43-ppc-pyk-gdhA for the efficient synthesis of γ-PGA was constructed through expression of glutamate synthesis features of Corynebacterium glutamicum, which increased the titer of γ-PGA by 2.18-fold (3.24 ± 0.22 g/L) compared to that of B. tequilensis BL01ΔpgdSΔggtΔsucAΔgudB (1.02 ± 0.11 g/L). To further improve the titer of γ-PGA and decrease the production of byproducts, three enzymes (Ppc, Pyk, and AceE) were assembled to a complex using SpyTag/Catcher pairs. The results showed that the γ-PGA titer of the assembled strain was 31.31% higher than that of the unassembled strain. To further reduce the production cost, 25.73 ± 0.69 g/L γ-PGA with a productivity of 0.48 g/L/h was obtained from cheap molasses. This work provides new metabolic engineering strategies to improve the production of γ-PGA in B. tequilensis BL01. Furthermore, the engineered strain has great potential for the industrial production of γ-PGA from molasses.

Catcher/Tag Toolbox: Biomolecular Click-Reactions For Protein Engineering Beyond Genetics

Manipulating protein architectures beyond genetic control has attracted widespread attention. Catcher/Tag systems enable highly specific conjugation of proteins in vivo and in vitro via an isopeptide-bond. They provide efficient, robust, and irreversible strategies for protein conjugation and are simple yet powerful tools for a variety of applications in enzyme industry, vaccines, biomaterials, and cellular applications. Here we summarize recent development of the Catcher/Tag toolbox with a particular emphasis on the design of Catcher/Tag pairs targeted for specific applications. We cover the current limitations of the Catcher/Tag systems and discuss the pH sensitivity of the reactions. Finally, we conclude some of the future directions in the development of this versatile protein conjugation method and envision that improved control over inducing the ligation reaction will further broaden the range of applications.

Thermostability enhancement of polyethylene terephthalate degrading PETase using self- and nonself-ligating protein scaffolding approaches

Polyethylene terephthalate (PET) hydrolase enzymes show promise for enzymatic PET degradation and green recycling of single-use PET vessels representing a major source of global pollution. Their full potential can be unlocked with enzyme engineering to render activities on recalcitrant PET substrates commensurate with cost-effective recycling at scale. Thermostability is a highly desirable property in industrial enzymes, often imparting increased robustness and significantly reducing quantities required. To date, most engineered PET hydrolases show improved thermostability over their parental enzymes. Here, we report engineered thermostable variants of Ideonella sakaiensis PET hydrolase enzyme (IsPETase) developed using two scaffolding strategies. The first employed SpyCatcher-SpyTag technology to covalently cyclize IsPETase, resulting in increased thermostability that was concomitant with reduced turnover of PET substrates compared to native IsPETase. The second approach using a GFP-nanobody fusion protein (vGFP) as a scaffold yielded a construct with a melting temperature of 80°C. This was further increased to 85°C when a thermostable PETase variant (FAST PETase) was scaffolded into vGFP, the highest reported so far for an engineered PET hydrolase derived from IsPETase. Thermostability enhancement using the vGFP scaffold did not compromise activity on PET compared to IsPETase. These contrasting results highlight potential topological and dynamic constraints imposed by scaffold choice as determinants of enzyme activity.

A single-domain protein catenane of dihydrofolate reductase

A single-domain protein catenane refers to two mechanically interlocked polypeptide rings that fold synergistically into a compact and integrated structure, which is extremely rare in nature. Here, we report a single-domain protein catenane of dihydrofolate reductase (cat-DHFR). This design was achieved by rewiring the connectivity between secondary motifs to introduce artificial entanglement and synthesis was readily accomplished through a series of programmed and streamlined post-translational processing events in cells without any additional in vitro reactions. The target molecule contained few exogenous motifs and was thoroughly characterized using a combination of ultra-performance liquid chromatography-mass spectrometry, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, protease cleavage experiments and ion mobility spectrometry-mass spectrometry. Compared with the linear control, cat-DHFR retained its catalytic capability and exhibited enhanced stability against thermal or chemical denaturation due to conformational restriction. These results suggest that linear proteins may be converted into their concatenated single-domain counterparts with almost identical chemical compositions, well-preserved functions and elevated stabilities, representing an entirely new horizon in protein science.

Analyzing Current Trends and Possible Strategies to Improve Sucrose Isomerases' Thermostability

Due to their ability to produce isomaltulose, sucrose isomerases are enzymes that have caught the attention of researchers and entrepreneurs since the 1950s. However, their low activity and stability at temperatures above 40 °C have been a bottleneck for their industrial application. Specifically, the instability of these enzymes has been a challenge when it comes to their use for the synthesis and manufacturing of chemicals on a practical scale. This is because industrial processes often require biocatalysts that can withstand harsh reaction conditions, like high temperatures. Since the 1980s, there have been significant advancements in the thermal stabilization engineering of enzymes. Based on the literature from the past few decades and the latest achievements in protein engineering, this article systematically describes the strategies used to enhance the thermal stability of sucrose isomerases. Additionally, from a theoretical perspective, we discuss other potential mechanisms that could be used for this purpose.

An Overview of Recent Developments in the Application of Antigen Displaying Vaccine Platforms: Hints for Future SARS-CoV-2 VLP Vaccines

Recently, a great effort has been devoted to studying attenuated and subunit vaccine development against SARS-CoV-2 since its outbreak in December 2019. It is known that diverse virus-like particles (VLPs) are extensively employed as carriers to display various antigenic and immunostimulatory cargo modules for vaccine development. Single or multiple antigens or antigenic domains such as the spike or nucleocapsid protein or their variants from SARS-CoV-2 could also be incorporated into VLPs via either a genetic or chemical display approach. Such antigen display platforms would help screen safer and more effective vaccine candidates capable of generating a strong immune response with or without adjuvant. This review aims to provide valuable insights for the future development of SARS-CoV-2 VLP vaccines by summarizing the latest updates and perspectives on the vaccine development of VLP platforms for genetic and chemical displaying antigens from SARS-CoV-2.

A novel self-purified auxiliary protein enhances the lichenase activity towards lichenan for biomass degradation

Due to the complex composition of lichenan, lichenase alone cannot always hydrolyze it efficiently. Carbohydrate-binding modules (CBMs) and lytic polysaccharide monooxygenases (LPMOs) have been confirmed to increase the hydrolysis efficiency of lichenases. However, their practical application was hampered by the complex and costly preparation procedure, as well as the poor stability of LPMOs. Herein, we discovered a novel and stable auxiliary protein named SCE to boost the hydrolysis efficiency. SCE was composed of SpyCatcher (SC) and elastin-like polypeptides (ELPs) and could be easily and cheaply prepared. Under the optimal conditions, the boosting degree for SCE/lichenase was 1.45, and the reducing sugar yield improved by nearly 45%. The results of high-performance liquid chromatography (HPLC) indicated that SCE had no influence on the hydrolysis pattern of lichenase. Through the experimental verification and bioinformatics analysis, we proposed the role of SCE in promoting the interaction between the lichenase and substrates. These findings endow SC with a novel function in binding to insoluble lichenan, paving the way for biomass degradation and biorefinery. KEY POINTS: • A novel self-purification auxiliary protein that could boost the hydrolysis efficiency of lichenase has been identified. • The protein is highly produced, simple to prepare, well stable, and does not require any external electron donor. • The novel function of SpyCatcher in binding to insoluble lichenan was first demonstrated.

Improving the specific activity and stability of alkaline pectinase PEL3 through SpyTag/SpyCatcher cyclization

OBJECTIVES

PEL3, an alkaline pectinase, exhibited the highest activity among documented alkaline pectate lyases reported in our early study. Unfortunately, undesired thermal stability hampering its industrial application. The purpose of this study is to enhance the performance of wild-type PEL3 (W-PEL3) based on SpyTag/SpyCatcher-mediated cyclization.

RESULTS

The cyclized PEL3 (C-PEL3) was observed to fold correctly and generate a spatial conformation in a head-to-tail manner in E. coli. C-PEL3 exhibited comparable optimum pH and temperature to those of W-PEL3. Moreover, the catalytic activity of C-PEL3 increased by 23% compared to W-PEL3, and the k_cat/K_m of C-PEL3 was 1.5-fold greater than that of the W-PEL3. Importantly, C-PEL3 showed improved stability compared to W-PEL3. Firstly, C-PEL3 displayed a 65% increase in residual activity after treatment at 55 °C for 30 min. Secondly, C-PEL3 was prone to resist heat-induced protein aggregation. Thirdly, C-PEL3 exhibited metal ion stability. Circular dichroism analysis revealed that C-PEL3 was more capable of maintaining its secondary structures than W-PEL3 upon heat treatment.

CONCLUSIONS

C-PEL3, the initial example of a circular pectinase through SpyTag/SpyCatcher cyclization, exhibits superior performance and represents a highly encouraging contender for industrial utilization.

Microbial β-glucanases: production, properties, and engineering

Lignocellulosic biomass, which mainly consists of cellulose and hemicellulose, is the most abundant renewable biopolymer on earth. β-Glucanases are glycoside hydrolases (GHs) that hydrolyze β-glucan, one of the dominant components of the plant cell wall, into cello-oligosaccharides and glucose. Among them, endo-β-1,4-glucanase (EC 3.2.1.4), exo-glucanase/cellobiohydrolase (EC 3.2.1.91), and β-glucosidase (EC 3.2.1.21) play critical roles in the digestion of glucan-like substrates. β-Glucanases have attracted considerable interest within the scientific community due to their applications in the feed, food, and textile industries. In the past decade, there has been considerable progress in the discovery, production, and characterization of novel β-glucanases. Advances in the development of next-generation sequencing techniques, including metagenomics and metatranscriptomics, have unveiled novel β-glucanases isolated from the gastrointestinal microbiota. The study of β-glucanases is beneficial for research and development of commercial products. In this study, we review the classification, properties, and engineering of β-glucanases.

Display of multiple proteins on engineered canine parvovirus-like particles expressed in cultured silkworm cells and silkworm larvae

Recent progress has been made dramatically in decorating virus-like particles (VLPs) on the surface or inside with functional molecules, such as antigens or nucleic acids. However, it is still challenging to display multiple antigens on the surface of VLP to meet the requirement as a practical vaccine candidate. Herein this study, we focus on the expression and engineering of the capsid protein VP2 of canine parvovirus for VLP display in the silkworm-expression system. The chemistry of the SpyTag/SpyCatcher (SpT/SpC) and SnoopTag/SnoopCatcher (SnT/SnC) are efficient protein covalent ligation systems to modify VP2 genetically, where SpyTag/SnoopTag are inserted into the N-terminus or two distinct loop regions (Lx and L2) of VP2. The SpC-EGFP and SnC-mCherry are employed as model proteins to evaluate their binding and display on six SnT/SnC-modified VP2 variants. From a series of protein binding assays between indicated protein partners, we showed that the VP2 variant with SpT inserted at the L2 region significantly enhanced VLP display to 80% compared to 5.4% from N-terminal SpT-fused VP2-derived VLPs. In contrast, the VP2 variant with SpT at the Lx region failed to form VLPs. Moreover, the SpT (Lx)/SnT (L2) double-engineered chimeric VP2 variants showed covalent conjugation capacity to both SpC/SnC protein partners. The orthogonal ligations between those binding partners were confirmed by both mixing purified proteins and co-infecting cultured silkworm cells or larvae with desired recombinant viruses. Our results indicate that a convenient VLP display platform was successfully developed for multiple antigen displays on demand. Further verifications can be performed to assess its capacity for displaying desirable antigens and inducing a robust immune response to targeted pathogens.

The synergism of lytic polysaccharide monooxygenases with lichenase and their co-immobilization on silica nanospheres for green conversion of lichen biomass

Enzyme-assisted valorization of lichenan represents a green and sustainable alternative to the conventional chemical industry. The recently discovered lytic polysaccharide monooxygenases (LPMOs) are essential components of state-of-the-art enzyme cocktails for lichenin bioconversion. The LPMOs named SpyTag fused LPMOs (AST) from Chaetomium globosum was functionally expressed in E. coli and exhibited 1.25-fold synergism with lichenase, whereas AST alone produced no detectable reducing sugars. HPLC results further confirm that AST does not alter the endogenous hydrolysis mode of lichenase but rather enhances its hydrolysis efficiency by disrupting the long chain of lichenan and releasing more reducing ends. To the best of our knowledge, this was the first report on the synergistic effect of LPMOs and lichenase, which may have great synergistic potential in the conversion of lichen biomass. Furthermore, a novel strategy for the covalently immobilizing AST and lichenase on silica nanoparticles (SNPs) from the cell lysate in a single step was proposed, which exhibited high activity recovery (82.9%) and high immobilization yield (94.8%). After 12 independent runs, about 67.4 % of the initial activity of the immobilized enzymes was retained. The resulted biocatalyst systems exhibited the green and sustainable strategy in the bioconversion of lichen biomass as well as other diverse polysaccharides.

Heterologous Expression of Thermotolerant α-Glucosidase in Bacillus subtilis 168 and Improving Its Thermal Stability by Constructing Cyclized Proteins

α-glucosidase is an essential enzyme for the production of isomaltooligosaccharides (IMOs). Allowing α-glucosidase to operate at higher temperatures (above 60 °C) has many advantages, including reducing the viscosity of the reaction solution, enhancing the catalytic reaction rate, and achieving continuous production of IMOs. In the present study, the thermal stability of α-glucosidase was significantly improved by constructing cyclized proteins. We screened a thermotolerant α-glucosidase (AGL) with high transglycosylation activity from Thermoanaerobacter ethanolicus JW200 and heterologously expressed it in Bacillus subtilis 168. After forming the cyclized α-glucosidase by different isopeptide bonds (SpyTag/SpyCatcher, SnoopTag/SnoopCatcher, SdyTag/SdyCatcher, RIAD/RIDD), we determined the enzymatic properties of cyclized AGL. The optimal temperature of all cyclized AGL was increased by 5 °C, and their thermal stability was generally improved, with SpyTag-AGL-SpyCatcher having a 1.74-fold increase compared to the wild-type. The results of molecular dynamics simulations showed that the RMSF values of cyclized AGL decreased, indicating that the rigidity of the cyclized protein increased. This study provides an efficient method for improving the thermal stability of α-glucosidase.

Programmable Polyproteams of Tyrosine Ammonia Lyases as Cross-Linked Enzymes for Synthesizing p-Coumaric Acid

Ideal immobilization with enhanced biocatalyst activity and thermostability enables natural enzymes to serve as a powerful tool to yield synthetically useful chemicals in industry. Such an enzymatic method strategy becomes easier and more convenient with the use of genetic and protein engineering. Here, we developed a covalent programmable polyproteam of tyrosine ammonia lyases (TAL-CLEs) by fusing SpyTag and SpyCatcher peptides into the N-terminal and C-terminal of the TAL, respectively. The resulting circular enzymes were clear after the spontaneous isopeptide bonds formed between the SpyTag and SpyCatcher. Furthermore, the catalytic performance of the TAL-CLEs was measured via a synthesis sample of p-Coumaric acid. Our TAL-CLEs showed excellent catalytic efficiency, with 98.31 ± 1.14% yield of the target product—which is 4.15 ± 0.08 times higher than that of traditional glutaraldehyde-mediated enzyme aggregates. They also showed over four times as much enzyme-activity as wild-type TAL does and demonstrated good reusability, and so may become a good candidate for industrial enzymes.

Peptide/protein-based macrocycles: from biological synthesis to biomedical applications

Living organisms have evolved cyclic or multicyclic peptides and proteins with enhanced stability and high bioactivity superior to their linear counterparts for diverse purposes. Herein, we review recent progress in applying this concept to artificial peptides and proteins to exploit the functional benefits of these macrocycles. Not only have simple cyclic forms been prepared, numerous macrocycle variants, such as knots and links, have also been developed. The chemical tools and synthetic strategies are summarized for the biological synthesis of these macrocycles, demonstrating it as a powerful alternative to chemical synthesis. Its further application to therapeutic peptides/proteins has led to biomedicines with profoundly improved pharmaceutical performances. Finally, we present our perspectives on the field and its future developments.

Protein-protein interactions enhance the thermal resilience of SpyRing-cyclized enzymes: A molecular dynamic simulation study

Recently a technique based on the interaction between adhesion proteins extracted from Streptococcus pyogenes, known as SpyRing, has been widely used to improve the thermal resilience of enzymes, the assembly of biostructures, cancer cell recognition and other fields. It was believed that the covalent cyclization of protein skeleton caused by SpyRing reduces the conformational entropy of biological structure and improves its rigidity, thus improving the thermal resilience of the target enzyme. However, the effects of SpyTag/ SpyCatcher interaction with this enzyme are poorly understood, and their regulation of enzyme properties remains unclear. Here, for simplicity, we took the single domain enzyme lichenase from Bacillus subtilis 168 as an example, studied the interface interactions in the SpyRing by molecular dynamics simulations, and examined the effects of the changes of electrostatic interaction and van der Waals interaction on the thermal resilience of target enzyme. The simulations showed that the interface between SpyTag/SpyCatcher and the target enzyme is different from that found by geometric matching method and highlighted key mutations at the interface that might have effect on the thermal resilience of the enzyme. Our calculations highlighted interfacial interactions between enzyme and SpyTag/SpyCatcher, which might be useful in rational designs of the SpyRing.

An antigen display system of GEM nanoparticles based on affinity peptide ligands

Gram-positive enhancer matrix (GEM) nanoparticles are often used in mucosal immunity, preparation of subunit vaccines or as an immune adjuvant due to its good immunological activities in recent years. Here, we designed and screened out a high affinity peptide ligand PL23, which could specifically target the non-epitope region of Classic Swine Fever Virus (CSFV) E2 protein, by virtual screening technology, enzyme linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR) test. The OD value of PL23 at 450 nm was reached 1.982, and the K_D value of it was 90.12 nM. Its binding capacity to protein was verified by SDS-PAGE as well. PL23 was subsequently conjugated to GEM nanoparticles by dehydration synthesis generating GEM-PL23 particles, and the GEM-PL-E2 particles were assembled after incubated with CSFV E2 protein. The cytotoxic test indicated that PL23, CSFV E2 protein, GEM nanoparticles, GEM-PL23 particles and GEM-PL-E2 particles were not toxic to cells and GEM nanoparticles could significantly promote the growth of APCs at high concentration for 1 h, p<0.001. In addition, GEM nanoparticles could promote the uptake of antigen by APCs. The cytokines tests suggested that GEM-PL-E2 particles could promote innate immune responses, regulate adaptive immune responses generated by T cells and APCs, and promote the differentiation and maturation of dendritic cells without producing inflammasomes. The results of immunological activity identification showed GEM-PL-E2 particles induced higher levels of both neutralizing antibodies and anti-CSFV antibodies than CSFV E2 protein in mice. This strategy provided a new, simpler, faster and cheaper method for assembling GEM nanoparticles, using an affinity peptide ligand replaced the protein anchor (PA), and provided a better application prospect for the application of GEM particles.

Higher Order Protein Catenation Leads to an Artificial Antibody with Enhanced Affinity and In Vivo Stability

The chemical topology is a unique dimension for protein engineering, yet the topological diversity and architectural complexity of proteins remain largely untapped. Herein, we report the biosynthesis of complex topological proteins using a rationally engineered, cross-entwining peptide heterodimer motif derived from p53dim (an entangled homodimeric mutant of the tetramerization domain of the tumor suppressor protein p53). The incorporation of an electrostatic interaction at specific sites converts the p53dim homodimer motif into a pair of heterodimer motifs with high specificity for directing chain entanglement upon folding. Its combination with split-intein-mediated ligation and/or SpyTag/SpyCatcher chemistry facilitates the programmed synthesis of protein heterocatenane or [n]catenanes in cells, leading to a general and modular approach to complex protein catenanes containing various proteins of interest. Concatenation enhances not only the target protein's affinity but also the in vivo stability as shown by its prolonged circulation time in blood. As a proof of concept, artificial antibodies have been developed by embedding a human epidermal growth factor receptor 2-specific affibody onto the [n]catenane scaffolds and shown to exhibit a higher affinity and a better pharmacokinetic profile than the wild-type affibody. These results suggest that topology engineering holds great promise in the development of therapeutic proteins.

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.

One-step construction of circularized nanodiscs using SpyCatcher-SpyTag

Circularized nandiscs (cNDs) exhibit superb monodispersity and have the potential to transform functional and structural studies of membrane proteins. In particular, cNDs can stabilize large patches of lipid bilayers for the reconstitution of complex membrane biochemical reactions, enabling the capture of crucial intermediates involved in synaptic transmission and viral entry. However, previous methods for building cNDs require multiple steps and suffer from low yields. We herein introduce a simple, one-step approach to ease the construction of cNDs using the SpyCatcher-SpyTag technology. This approach increases the yield of cNDs by over 10-fold and is able to rapidly generates cNDs with diameters ranging from 11 to over 100 nm. We demonstrate the utility of these cNDs for mechanistic interrogations of vesicle fusion and protein-lipid interactions that are unattainable using small nanodiscs. Together, the remarkable performance of SpyCatcher-SpyTag in nanodisc circularization paves the way for the use of cNDs in membrane biochemistry and structural biology.

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.

Research progress and the biotechnological applications of multienzyme complex

The multienzyme complex system has become a research focus in synthetic biology due to its highly efficient overall catalytic ability and has been applied to various fields. Multienzyme complexes are formed by cascading complexes, which are multiple functionally related enzymes that continuously and efficiently catalyze the production of substrates. Compared with current mainstream microbial cell catalytic systems, in vitro multienzyme molecular machines have many advantages, such as fewer side reactions, a high product yield, a fast reaction speed, easy product separation, a tolerable toxic environment, and robust system operability, showing increasing competitiveness in the field of biomanufacturing. In this review, the research progress of multienzyme complexes in nature and multienzyme cascades in vivo or in vitro will be introduced, and the discovered enzyme cascades concerning scaffolding proteins will also be discussed. This review is expected to provide a more theoretical basis for the modification of multienzyme complexes and broaden their application in the field of synthetic biology. KEY POINTS: • The cascade reactions of some natural multienzyme complexes are reviewed. • The main approaches of constructing artificial multienzyme complexes are summarized. • The structure and application of cellulosomes are discussed and prospected.

A novel all-in-one strategy for purification and immobilization of β-1,3-xylanase directly from cell lysate as active and recyclable nanobiocatalyst

BACKGROUND

Exploring a simple and versatile technique for direct immobilization of target enzymes from cell lysate without prior purification is urgently needed. Thus, a novel all-in-one strategy for purification and immobilization of β-1,3-xylanase was proposed, the target enzymes were covalently immobilized on silica nanoparticles via elastin-like polypeptides (ELPs)-based biomimetic silicification and SpyTag/SpyCatcher spontaneous reaction. Thus, the functional carriers that did not require the time-consuming surface modification step were quickly and efficiently prepared. These carriers could specifically immobilize the SpyTag-fused target enzymes from the cell lysate without pre-purification.

RESULTS

The ELPs-SpyCatcher hardly leaked from the carriers (0.5%), and the immobilization yield of enzyme was up to 96%. Immobilized enzyme retained 85.6% of the initial activity and showed 88.6% of the activity recovery. Compared with free ones, the immobilized β-1,3-xylanase showed improved thermal stability, elevated storage stability and good pH tolerance. It also retained more than 70.6% of initial activity after 12 reaction cycles, demonstrating its excellent reusability.

CONCLUSIONS

The results clearly highlighted the effectiveness of the novel enzyme immobilization method proposed here due to the improvement of overall performance of immobilized enzyme in respect to free form for the hydrolysis of macromolecular substrates. Thus, it may have great potential in the conversion of algae biomass as well as other related fields.

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.

Topology engineering via protein catenane construction to strengthen an industrial biocatalyst

Protein topology engineering has emerged as a new dimension to alter protein stability and function. Inspired by the art of nature, where backbone cyclization is frequently adopted to enhance the stability of natural peptide products and thermostable enzymes; herein, we report protein topology engineering of an industrial thermolabile gamma lactamase via catenation. Two different protein catenanes were successfully constructed via SpyTag/SpyCatcher modules and two different peptide dimer domains. The designed protein catenanes were functionally synthesized in Escherichia coli. A comparison of their biochemical properties revealed that protein topology played a key role in the stability of gamma lactamase. Protein catenation enhanced both the thermo- and proteolytic stabilities of gamma lactamase. Gamma lactamase was stabilized by ∼8 °C in one of the catenated forms. Moreover, Cat1-MhIHL-V54L and Cat2-MhIHL-V54L displayed 1.8- and 2.4-fold higher enzyme efficiencies (Kcat/Km), respectively, than the unattenuated enzyme. Therefore, our results proved that protein catenane construction could be a general strategy to strengthen industrial biocatalysts by mechanisms distinct from those of the conventional direct evolution schemes, whereby our results offer wide applications in the fine chemical industry.

Bacillus subtilis: a universal cell factory for industry, agriculture, biomaterials and medicine

Due to its clear inherited backgrounds as well as simple and diverse genetic manipulation systems, Bacillus subtilis is the key Gram-positive model bacterium for studies on physiology and metabolism. Furthermore, due to its highly efficient protein secretion system and adaptable metabolism, it has been widely used as a cell factory for microbial production of chemicals, enzymes, and antimicrobial materials for industry, agriculture, and medicine. In this mini-review, we first summarize the basic genetic manipulation tools and expression systems for this bacterium, including traditional methods and novel engineering systems. Secondly, we briefly introduce its applications in the production of chemicals and enzymes, and summarize its advantages, mainly focusing on some noteworthy products and recent progress in the engineering of B. subtilis. Finally, this review also covers applications such as microbial additives and antimicrobials, as well as biofilm systems and spore formation. We hope to provide an overview for novice researchers in this area, offering them a better understanding of B. subtilis and its applications.

Enzymatic degradation of algal 1,3-xylan: from synergism of lytic polysaccharide monooxygenases with β-1,3-xylanases to their intelligent immobilization on biomimetic silica nanoparticles

Lytic polysaccharide monooxygenases (LPMOs) with synergistic effect on polysaccharide hydrolase represent a revolution in biotechnology, which may accelerate the conversion of biomass to the second-generation biofuels. Discovering more hydrolases that have synergism with LPMOs will considerably expand the knowledge and application of biomass degradation. The LPMOs named CgAA9 were verified to exhibit 1.52-fold synergism when incubated with β-1,3-xylanase at a molar ratio of 3:1. The ion chromatography results proved that CgAA9 did not alter the endogenous hydrolysis mode of β-1,3-xylanase. Meanwhile, to decrease the operational cost of enzymes, a novel strategy for immobilizing LPMOs and β-1,3-xylanases based on the biomimetic silica nanoparticles was developed. It enabled preparation of immobilized enzymes directly from the cell lysate. The immobilization efficiency and activity recovery reached 84.6 and 81.4%. They showed excellent reusability for 12 cycles by retaining 68% of initial activity. The optimum temperature for both free and immobilized biocatalyst were 40 and 37 °C, indicating they were ideal candidates for typical simultaneous saccharification and fermentation (SSF) in ethanol production from algea biomass. This was the first report on the synergy between LPMOs and β-1,3-xylanase, and the strategy for enzyme self-immobilization was simple, timesaving, and efficient, which might have great potentials in algae biomass hydrolysis. KEY POINTS: • The lytic polysaccharide monooxygenases (LPMOs) from Chaetomium globosum were firstly verified to boost the hydrolysis of β-1,3-xylanases for β-1,3-xylan. • A novel strategy for simple preparation of SpyCather-modifed silica nanopartilcles and intelligent immobilization of target enzymes from the cell lysate was proposed. • The immobilized LPMOs and β-1,3-xylanases could be reasonable alternatives for typical simultaneous saccharification and fermentation (SSF) in manipulation of algae biomass.

Generation of biparatopic antibody through two-step targeting of fragment antibodies on antigen using SpyTag and SpyCatcher

Biparatopic fragment antibodies can overcome deficiencies in avidity of conventional antibody fragments. Here, we describe a technology for generating biparatopic antibodies through two-step targeting using a pair of polypeptides, SpyTag and SpyCatcher, that spontaneously react to form a covalent bond between antibody fragments. In this method, two antibody fragments, each targeting different epitopes of the antigen, are fused to SpyTag and to SpyCatcher. When the two polypeptides are serially added to the antigen, their proximity on the antigen results in covalent bond formation and generation of a biparatopic antibody. We validated the system with purified recombinant antigen. Results in antigen-overexpressing cells were promising although further optimization will be required. Because this strategy results in high-affinity targeting with a bipartite molecule that has considerably lower molecular weight than an antibody, this technology is potentially useful for diverse applications.

From Synthesis to Characterization of Site-Selective PEGylated Proteins

Covalent attachment of therapeutic proteins to polyethylene glycol (PEG) is widely used for the improvement of its pharmacokinetic and pharmacological properties, as well as the reduction in reactogenicity and related side effects. This technique named PEGylation has been successfully employed in several approved drugs to treat various diseases, even cancer. Some methods have been developed to obtain PEGylated proteins, both in multiple protein sites or in a selected amino acid residue. This review focuses mainly on traditional and novel examples of chemical and enzymatic methods for site-selective PEGylation, emphasizing in N-terminal PEGylation, that make it possible to obtain products with a high degree of homogeneity and preserve bioactivity. In addition, the main assay methods that can be applied for the characterization of PEGylated molecules in complex biological samples are also summarized in this paper.

Characterization of Thermostable and Chimeric Enzymes via Isopeptide Bond-Mediated Molecular Cyclization

Mannooligosaccharides are released by mannan-degrading endo-β-1,4-mannanase and are known as functional additives in human and animal diets. To satisfy demands for biocatalysis and bioprocessing in crowed environments, in this study, we employed a recently developed enzyme-engineering system, isopeptide bond-mediated molecular cyclization, to modify a mesophilic mannanase from Bacillus subtilis. The results revealed that the cyclized enzymes showed enhanced thermostability and ion stability and resilience to aggregation and freeze-thaw treatment by maintaining their conformational structures. Additionally, by using the SpyTag/SpyCatcher system, we generated a mannanase-xylanase bifunctional enzyme that exhibited a synergistic activity in substrate deconstruction without compromising substrate affinity. Interestingly, the dual-enzyme ring conformation was observed to be more robust than the linear enzyme but inferior to the single-enzyme ring conformation. Taken together, these findings provided new insights into the mechanisms of molecular cyclization on stability improvement and will be useful in the production of new functional oligosaccharides and feed additives.

Programmable stimuli-responsive polypeptides for biomimetic synthesis of silica nanocomposites and enzyme self-immobilization

Bioinspired silicification is an attractive route for achieving unique silica nanocomposites. Herein, a novel, facile and inexpensive route for biosilica synthesis is developed using the stimuli-responsive elastin-like polypeptide (ELP). The ELP is precisely tailored to a silica-mineralizing peptide by programming it with lysine residues. The resulting cationic ELP[KV₈F-40] is purified in ultrahigh yield using a chromatography-free ITC purification technique based on thermal-responsive property. Excitingly, the specific activity of ELP is 40-fold higher than that of silaffin. Besides, efficient and strong entrapment of ELP is achieved with over 98% of immobilization yield and less than 2% of leakage. These imply that cationic ELP may be used as a bifunctional tag (purification and immobilization) for fusion protein. An enzyme (xylanase) is therefore chosen to genetically fuse to ELP. The ELP-fused xylanase is purified by ELP with high purity (~98%) and enables the rapid (within minutes) self-immobilization. The immobilization yield was greater than 95%, and the immobilized xylanases hardly leaked from the silica matrix, demonstrating high efficiency of the self-immobilization process. The strategy developed here may provide a new opportunity for fabricating functional silica nanocomposites in a feasible and inexpensive pathway, which will have great potentials in the field of biotechnology.

Catching a SPY: Using the SpyCatcher-SpyTag and Related Systems for Labeling and Localizing Bacterial Proteins

The SpyCatcher-SpyTag system was developed seven years ago as a method for protein ligation. It is based on a modified domain from a Streptococcus pyogenes surface protein (SpyCatcher), which recognizes a cognate 13-amino-acid peptide (SpyTag). Upon recognition, the two form a covalent isopeptide bond between the side chains of a lysine in SpyCatcher and an aspartate in SpyTag. This technology has been used, among other applications, to create covalently stabilized multi-protein complexes, for modular vaccine production, and to label proteins (e.g., for microscopy). The SpyTag system is versatile as the tag is a short, unfolded peptide that can be genetically fused to exposed positions in target proteins; similarly, SpyCatcher can be fused to reporter proteins such as GFP, and to epitope or purification tags. Additionally, an orthogonal system called SnoopTag-SnoopCatcher has been developed from an S. pneumoniae pilin that can be combined with SpyCatcher-SpyTag to produce protein fusions with multiple components. Furthermore, tripartite applications have been produced from both systems allowing the fusion of two peptides by a separate, catalytically active protein unit, SpyLigase or SnoopLigase. Here, we review the current state of the SpyCatcher-SpyTag and related technologies, with a particular emphasis on their use in vaccine development and in determining outer membrane protein localization and topology of surface proteins in bacteria.

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

SpyTag and SpyCatcher can spontaneously and rapidly conjugate to form an irreversible and stable covalent bond. The trehalose synthase (TreS) from Thermomonospora curvata was successfully cyclized after the fusion of a SpyTag to its C-terminus and SpyCatcher to the N-terminus. Cyclized TreS retained more than 85% of its activity at temperatures ranging from 40 to 50°C and more than 95% at a pH range of 8 to 10, while the wild type kept only 60 and 80% of its activity under the same conditions. These results demonstrated that cyclized TreS had better resistance to high temperature and alkali than the wild type. Furthermore, structural analysis revealed that cyclized TreS had better conformational stability and was able to fold correctly at a higher temperature than the wild type. Our findings indicate that the use of SpyTag and SpyCatcher to cyclize enzymes is a promising strategy to increase their stability.