Microbial transglutaminase for biotechnological and biomedical engineering

Transglutaminase-mediated stiffening of the glomerular basement membrane mitigates pressure-induced reductions in molecular sieving coefficient by reducing compression

Proteinuria, the presence of high molecular weight proteins in the urine, is a primary indicator of chronic kidney disease. Proteinuria results from increased molecular permeability of the glomerular filtration barrier combined with saturation or defects in tubular protein reabsorption. Any solute that passes into the glomerular filtrate traverses the glomerular endothelium, the glomerular basement membrane, and the podocyte slit diaphragm. Damage to any layer of the filter has reciprocal effects on other layers to increase glomerular permeability. The GBM is thought to act as a compressible ultrafilter that has increased molecular selectivity with increased pressure due to compression that reduced the porosity of the GBM with increased pressure. In multiple forms of chronic kidney disease, crosslinking enzymes are upregulated and may act to increase GBM stiffness. Here we show that enzymatically crosslinking porcine GBM with transglutaminase increases the stiffness of the GBM and mitigates pressure-dependent reductions in molecular sieving coefficient. This was modeled mathematically using a modified membrane transport model accounting for GBM compression. Changes in the mechanical properties of the GBM may contribute to proteinuria through pressure-dependent effects on GBM porosity.

Promiscuous Enzymes for Residue-Specific Peptide and Protein Late-Stage Functionalization

The late-stage functionalization of peptides and proteins holds significant promise for drug discovery and facilitates bioorthogonal chemistry. This selective functionalization leads to innovative advances in in vitro and in vivo biological research. However, it is a challenging endeavor to selectively target a certain amino acid or position in the presence of other residues containing reactive groups. Biocatalysis has emerged as a powerful tool for selective, efficient, and economical modifications of molecules. Enzymes that have the ability to modify multiple complex substrates or selectively install nonnative handles have wide applications. Herein, we highlight enzymes with broad substrate tolerance that have been demonstrated to modify a specific amino acid residue in simple or complex peptides and/or proteins at late-stage. The different substrates accepted by these enzymes are mentioned together with the reported downstream bioorthogonal reactions that have benefited from the enzymatic selective modifications.

Transglutaminase in Foods and Biotechnology

Stabilization and reusability of enzyme transglutaminase (TGM) are important goals for the enzymatic process since immobilizing TGM plays an important role in different technologies and industries. TGM can be used in many applications. In the food industry, it plays a role as a protein-modifying enzyme, while, in biotechnology and pharmaceutical applications, it is used in mediated bioconjugation due to its extraordinary crosslinking ability. TGMs (EC 2.3.2.13) are enzymes that catalyze the formation of a covalent bond between a free amino group of protein-bound or peptide-bound lysine, which acts as an acyl acceptor, and the γ-carboxamide group of protein-bound or peptide-bound glutamine, which acts as an acyl donor. This results in the modification of proteins through either intramolecular or intermolecular crosslinking, which improves the use of the respective proteins significantly.

Design and Evolution of Enhanced Peptide-Peptide Ligation for Modular Transglutaminase Assembly

Robust and precise tools are needed to enhance the functionality and resilience of synthetic nanoarchitectures. Here, we have employed directed evolution and rational design to build a fast-acting molecular superglue from a bacterial adhesion protein. We have generated the SnoopLigase2 coupling system, a genetically encoded route for efficient transamidation between SnoopTag2 and DogTag2 peptides. Each peptide was selected for rapid reaction by phage display screening. The optimized set allows more than 99% completion and is compatible with diverse buffers, pH values, and temperatures, accelerating the reaction over 1000-fold. SnoopLigase2 directs a specific reaction in the mammalian secretory pathway, allowing covalent display on the plasma membrane. Transglutaminase 2 (TG2) has a network of interactions and substrates amidst the mammalian cell surface and extracellular matrix. We expressed a modified TG2 with resistance to oxidative inactivation and minimal self-reactivity. SnoopLigase2 enables TG2 functionalization with transforming growth factor alpha (TGFα) in routes that would be impossible through genetic fusion. The TG2:TGFα conjugate retained transamidase activity, stably anchored TGFα for signal activation in the extracellular environment, and reprogrammed cell behavior. This modular toolbox should create new opportunities for molecular assembly, both for novel biomaterials and complex cellular environments.

Crosslinking Mechanism on a Novel Bacillus cereus Transglutaminase-Mediated Conjugation of Food Proteins

Until now, Streptoverticillium mobaraense transglutaminase (TG) is the only commercialized TG, but limited information is known about its selection tendency on crosslinking sites at the protein level, restricting its application in the food industry. Here, four recombinant Bacillus TGs were stable in a broad range of pH (5.0−9.0) and temperatures (<50 °C), exhibiting their maximum activity at 50−60 °C and pH 6.0−7.0. Among them, TG of B. cereus (BCETG) demonstrated the maximal specific activity of 177 U/mg. A structural analysis indicated that the Ala147-Ala156 region in the substrate tunnel of BCETG played a vital role in catalytic activity. Furthermore, bovine serum albumin, as well as nearly all protein ingredients in soy protein isolate and whey protein, could be cross-linked by BCETG, and the internal crosslinking paths of three protein substrates were elucidated. This study demonstrated Bacillus TGs are a candidate for protein crosslinking and provided their crosslinking mechanism at the protein level for applications in food processing.

Rational design of a disulfide bridge increases the thermostability of microbial transglutaminase

Microbial transglutaminase (MTG) has numerous industrial applications in the food and pharmaceutical sectors. Unfortunately, the thermostability of MTG is too low to tolerate the desired conditions used in many of these commercial processes. In a previous study, we used protein engineering to improve the thermostability of MTG. Specifically, we generated a T7C/E58C mutant of MTG from Streptomyces mobaraensis that displayed enhanced resistance to thermal inactivation. In this study, a rational structure-based approach was adopted to introduce a disulfide bridge to further increase the thermostability of MTG. In all, four new mutants, each containing a novel disulfide bond, were engineered. Of these four mutants, D3C/G283C showed the most promising thermostability with a significantly higher ∆T₅₀ (defined as the temperature of incubation at which 50% of the initial activity remains) of + 9 °C by comparison to wild-type MTG. Indeed, D3C/G283C combined enhanced thermostability with a 2.1-fold increased half-life at 65 °C compared with the wild-type enzyme. By structure-based rational design, we were able to create an MTG variant which might be useful for expanding the scope of application in food. KEY POINTS: • Microbial transglutaminase (MTG) is an enzyme used in many food applications • The applicability of MTG to various industrial processes other than the food sector is being investigated • Improvement of thermostability was confirmed for the disulfide bridge mutant D3C/G283C.

Microbial Transglutaminase-Mediated Formation of Erythropoietin-Polyester Conjugates

Erythropoietin (EPO) is a glycoprotein hormone that has been used to treat anemia in patients with chronic kidney disease and in cancer patients who are receiving chemotherapy. Here, we investigated the accessibility of the glutamine (Gln, Q) residues of recombinant human erythropoietin (rHuEPO) towards a thermoresistant variant microbial transglutaminase (mTGase), TG¹⁶ with the aim of developing novel rHuEPO conjugates that may potentially enhance its biological efficacy. As a model bioconjugation, we studied the reactivity of rHuEPO towards TG¹⁶ with a low molar mass amine group containing substrate, monodansyl cadaverine (MDC). The reactions were carried out at a T_m of 54.3 °C, the transition temperature of rHuEPO. Characterization by SDS-PAGE and mass spectrometry confirmed the conjugates formation. Then, we examined the conjugation of rHuEPO with a biodegradable and biocompatible polyester, poly(D-sorbitol adipate) (PDSA). To achieve this, PDSA was enzymatically synthesized using lipase B from Candida antartica (CAL-B), chemically modified with side chains having free primary amine (NH₂) groups that can be acyl acceptor substrate of TG¹⁶, thoroughly characterized by ¹H NMR spectroscopy, and then applied for the TG¹⁶-mediated conjugation reaction with rHuEPO. rHuEPO conjugates generated by this approach were identified by SDS-PAGE proving that the amine-grafted PDSA is accepted as a substrate for TG¹⁶. The successful conjugation was further verified by the detection of high molar mass fluorescent bands after labelling of amine-grafted PDSA with rhodamine B-isothiocyanate. Overall, this enzymatic procedure is considered as an effective approach to prepare biodegradable rHuEPO-polymer conjugates even in the presence of N- and O-glycans.

Effect of key regulators in augmenting transcriptional expression of Transglutaminase in Streptomyces mobaraensis

Transglutaminase forms isopeptide bonds in proteins which are helpful in various industrial applications. However, low productivity and high cost are the major bottlenecks for industrial Transglutaminase production. The present study describes the regulatory mechanism of microbial Transglutaminase (MTGase) biosynthesis from Streptomyces mobaraensis and the effect of key regulators to maximize production. The transcriptional responses under the effect of various key modulators of MTGasebiosynthesis were evaluated. Productivity of MTGase with novel biosynthesis approach by regulators augmentation was correlated by transcriptional profiling. The optimization by key modulators by combinational supplementation led to 2-fold rise in activity. The functional attributes, the copy number of MTGase gene and relative changes were assessed by Real-Time quantitative PCR. Protease, MgCl₂, CTAB induced upregulation, whereas PMSF, NaF and bleomycin sulphate showed inhibitory action on MTGase production and activity. The optimization by combinational supplementation of key modulators led to 4.27-fold increase (6.11 IU/mL) in production.

Microbial transglutaminase nanoflowers as an alternative nanomedicine for breast cancer theranostics

Breast cancer is the most common malignancy among women. With the aim of decreasing the toxicity of conventional breast cancer treatments, an alternative that could provide appropriate and effective drug utilization was envisioned. Thus, we contemplated and compared the in vitro effects of microbial transglutaminase nanoflowers (MTGase NFs) on breast cancer cells (MCF-7). Transglutaminase is an important regulatory enzyme acting as a site-specific cross-linker for proteins. With the versatility of MTGase facilitating the nanoflower formation by acting as molecular glue, it was demonstrated to have anti-cancer properties. The rational drug design based on a transglutaminase enzyme-assisted approach led to the uniform shape of petals in these nanoflowers, which had the capacity to act directly as an anti-cancer drug. Herein, we report the anti-cancer characteristics portrayed by enzymatic MTGase NFs, which are biocompatible in nature. This study demonstrated the prognostic and therapeutic significance of MTGase NFs as a nano-drug in breast cancer treatment. The results on MCF-7 cells showed a significantly improved in vitro therapeutic efficacy. MTGase NFs were able to exhibit inhibitory effects on cell viability (IC₅₀-8.23 μg ml⁻¹) within 24 h of dosage. To further substantiate its superior anti-proliferative role, the clonogenic potential was measured to be 62.8%, along with migratory inhibition of cells (3.76-fold change). Drastic perturbations were induced (4.61-fold increase in G0/G1 phase arrest), pointed towards apoptotic induction with a 58.9% effect. These results validated the role of MTGase NFs possessing a cytotoxic nature in mitigating breast cancer. Thus, MTGase bestows distinct functionality towards therapeutic nano-modality, i.e., nanoflowers, which shows promise in cancer treatment.

Development of a novel therapeutic nano-modality in the form of enzymatic transglutaminase nanoflowers; endowed with anti-cancerous action against breast cancers.

Microbial Transglutaminase Is a Very Frequently Used Food Additive and Is a Potential Inducer of Autoimmune/Neurodegenerative Diseases

Microbial transglutaminase (mTG) is a heavily used food additive and its industrial transamidated complexes usage is rising rapidly. It was classified as a processing aid and was granted the GRAS (generally recognized as safe) definition, thus escaping full and thorough toxic and safety evaluations. Despite the manufacturers claims, mTG or its cross-linked compounds are immunogenic, pathogenic, proinflammatory, allergenic and toxic, and pose a risk to public health. The enzyme is a member of the transglutaminase family and imitates the posttranslational modification of gluten, by the tissue transglutaminase, which is the autoantigen of celiac disease. The deamidated and transamidated gliadin peptides lose their tolerance and induce the gluten enteropathy. Microbial transglutaminase and its complexes increase intestinal permeability, suppresses enteric protective pathways, enhances microbial growth and gliadin peptide’s epithelial uptake and can transcytose intra-enterocytically to face the sub-epithelial immune cells. The present review updates on the potentially detrimental side effects of mTG, aiming to interest the scientific community, induce food regulatory authorities’ debates on its safety, and protect the public from the mTG unwanted effects.

Convenient Genetic Encoding of Phenylalanine Derivatives through Their α-Keto Acid Precursors

The activity and function of proteins can be improved by incorporation of non-canonical amino acids (ncAAs). To avoid the tedious synthesis of a large number of chiral phenylalanine derivatives, we synthesized the corresponding phenylpyruvic acid precursors. Escherichia coli strain DH10B and strain C321.ΔA.expΔPBAD were selected as hosts for phenylpyruvic acid bioconversion and genetic code expansion using the MmPylRS/^pyltRNA_CUA system. The concentrations of keto acids, PLP and amino donors were optimized in the process. Eight keto acids that can be biotransformed and their coupled genetic code expansions were identified. Finally, the genetic encoded ncAAs were tested for incorporation into fluorescent proteins with keto acids.

Enzymatic Methods for the Site-Specific Radiolabeling of Targeting Proteins

Site-specific conjugation of proteins is currently required to produce homogenous derivatives for medicine applications. Proteins derivatized at specific positions of the polypeptide chain can actually show higher stability, superior pharmacokinetics, and activity in vivo, as compared with conjugates modified at heterogeneous sites. Moreover, they can be better characterized regarding the composition of the derivatization sites as well as the conformational and activity properties. To this aim, several site-specific derivatization approaches have been developed. Among these, enzymes are powerful tools that efficiently allow the generation of homogenous protein-drug conjugates under physiological conditions, thus preserving their native structure and activity. This review will summarize the progress made over the last decade on the use of enzymatic-based methodologies for the production of site-specific labeled immunoconjugates of interest for nuclear medicine. Enzymes used in this field, including microbial transglutaminase, sortase, galactosyltransferase, and lipoic acid ligase, will be overviewed and their recent applications in the radiopharmaceutical field will be described. Since nuclear medicine can benefit greatly from the production of homogenous derivatives, we hope that this review will aid the use of enzymes for the development of better radio-conjugates for diagnostic and therapeutic purposes.

Effect of introducing a disulfide bridge on the thermostability of microbial transglutaminase from Streptomyces mobaraensis

Microbial transglutaminase (MTG) has been used extensively in academic research and the food industry through cross-linking or posttranslational modification of proteins. In our previous paper, the activity-increased MTG mutants were obtained by means of rational mutagenesis and random mutagenesis coupled with the newly developed screening system. In addition, the improvement of heat resistance of MTG is needed to expand further its industrial applications. Here, a structure-based rational enzyme engineering approach was applied to improve the thermostability of MTG by introducing an artificial disulfide bridge. As a result of narrowing down candidates using a rational approach, we successfully engineered a disulfide bridge into the N-terminal region of MTG by substituting Thr-7 and Glu-58 with cysteine. The T7C/E58C mutant was observed to have a de novo disulfide bridge and showed an increased melting temperature (Tm value) of 4.3 °C with retained enzymatic activity. To address the benefit-gained reason, we focused on the Cβ temperature factor of the amino-acid residues that might form a disulfide bridge in MTG. Introducing the disulfide bridge had no remarkable effect on the mutant aiming to stabilize the high temperature factor. On the other hand, the mutation was effective on the relatively stable region. The introduction of a disulfide bridge may therefore be effective to stabilize further the relatively stable part. This finding is considered to be useful for the rational design of mutants aiming at heat resistance of proteins.Key Points• Microbial transglutaminase (MTG) is used as a binder in the food industry.• MTG has the potential for use in the manufacturing of various commercial materials.• Enhanced thermostability was observed for the disulfide bridge mutant, T7C/G58C.

Intein-mediated intracellular production of active microbial transglutaminase in Corynebacterium glutamicum

The microbial transglutaminase (mTGase) from Streptomyces mobaraense is widely used in the food industry. However, recombinant production of mTGase is challenging because the mTGase is synthesized as an inactive zymogen, and needs to be activated by proteolytic processing. In this study, self-cleaving intein Ssp DnaB was applied to activate the mTGase in Corynebacterium glutamicum. Premature cleavage of intein Ssp DnaB also occurred, but instead of suppressing premature cleavage, this phenomenon was used to produce active mTGase in C. glutamicum. Both SDS-PAGE analysis and mTGase activity assays indicated that the premature cleavage of intein Ssp DnaB activated the mTGase intracellularly in C. glutamicum. The subsequent N-terminal amino acid sequencing and site-directed mutagenesis studies further showed that the premature cleavage activated the mTGase intracellularly, in a highly specific manner. Moreover, the growth performance of C. glutamicum was not noticeably affected by the intracellular expression of active mTGase. Finally, the mTGase was produced in a 2 L bioreactor, with activity up to 49 U/mL, the highest intracellular mTGase activity ever reported. Using premature cleavage of intein Ssp DnaB to activate mTGase in C. glutamicum, we produced high levels of intracellular active mTGase. Moreover, this approach did not require any further processing steps, such as protease treatment or lengthy incubation, greatly simplifying the production of active mTGase. This efficient and simple approach has great potential for the large-scale industrial production of active mTGase.

Glutamine-walking: Creating reactive substrates for transglutaminase-mediated protein labeling

Chemically modified proteins are increasingly being tested and approved as therapeutic products. Batch-to-batch homogeneity is crucial to ensure safety and quality of therapeutic products. Highly selective protein modification may be achieved using enzymatic routes. Microbial transglutaminase (mTG) is a robust, easy to use and well-established enzyme that is used at a very large scale in the food industry such that its efficacy and its safety for human consumption are well established. In the context of therapeutic protein modification, mTG should crosslink one or more glutamines on the target protein with an aminated moiety such as a solubilizer, a tracer or a cytotoxic moiety. mTG has the advantage of being unreactive toward the majority of surface-exposed glutamines on most proteins, reducing sample heterogeneity. The caveat is that there may be no reactive glutamine on the target protein, or else a reactive glutamine may be found in a location where its modification compromises function of the target protein. Here we describe the glutamine-walk (Gln-walk), a straightforward method to create a glutamine-substrate site that is reactive to mTG in a target protein. Iterative substitution of single amino acids to a glutamine is followed by facile identification of reactivity with mTG, where covalent labeling of the target with an aminated fluorophore allows visualization of the most reactive modified targets. The approach is empirical; knowledge of the target protein structure and functional regions facilitates application of the method.

Greatest Hits-Innovative Technologies for High Throughput Identification of Bispecific Antibodies

Recent years have shown a tremendous increase and diversification in antibody-based therapeutics with advances in production techniques and formats. The plethora of currently investigated bi- to multi-specific antibody architectures can be harnessed to elicit a broad variety of specific modes of actions in oncology and immunology, spanning from enhanced selectivity to effector cell recruitment, all of which cannot be addressed by monospecific antibodies. Despite continuously growing efforts and methodologies, the identification of an optimal bispecific antibody as the best possible combination of two parental monospecific binders, however, remains challenging, due to tedious cloning and production, often resulting in undesired extended development times and increased expenses. Although automated high throughput screening approaches have matured for pharmaceutical small molecule development, it was only recently that protein bioconjugation technologies have been developed for the facile generation of bispecific antibodies in a 'plug and play' manner. In this review, we provide an overview of the most relevant methodologies for bispecific screening purposes-the DuoBody concept, paired light chain single cell production approaches, Sortase A and Transglutaminase, the SpyTag/SpyCatcher system, and inteins-and elaborate on the benefits as well as drawbacks of the different technologies.

Kinetics and Optimization of the Lysine-Isopeptide Bond Forming Sortase Enzyme from Corynebacterium diphtheriae

Site-specifically modified protein bioconjugates have important applications in biology, chemistry, and medicine. Functionalizing specific protein side chains with enzymes using mild reaction conditions is of significant interest, but remains challenging. Recently, the lysine-isopeptide bond forming activity of the sortase enzyme that builds surface pili in Corynebacterium diphtheriae (CdSrtA) has been reconstituted in vitro. A mutationally activated form of CdSrtA was shown to be a promising bioconjugating enzyme that can attach Leu-Pro-Leu-Thr-Gly peptide fluorophores to a specific lysine residue within the N-terminal domain of the SpaA protein (NSpaA), enabling the labeling of target proteins that are fused to NSpaA. Here we present a detailed analysis of the CdSrtA catalyzed protein labeling reaction. We show that the first step in catalysis is rate limiting, which is the formation of the CdSrtA-peptide thioacyl intermediate that subsequently reacts with a lysine ε-amine in NSpaA. This intermediate is surprisingly stable, limiting spurious proteolysis of the peptide substrate. We report the discovery of a new enzyme variant (CdSrtAΔ) that has significantly improved transpeptidation activity, because it completely lacks an inhibitory polypeptide appendage ("lid") that normally masks the active site. We show that the presence of the lid primarily impairs formation of the thioacyl intermediate and not the recognition of the NSpaA substrate. Quantitative measurements reveal that CdSrtAΔ generates its cross-linked product with a catalytic turnover number of 1.4 ± 0.004 h-1 and that it has apparent KM values of 0.16 ± 0.04 and 1.6 ± 0.3 mM for its NSpaA and peptide substrates, respectively. CdSrtAΔ is 7-fold more active than previously studied variants, labeling >90% of NSpaA with peptide within 6 h. The results of this study further improve the utility of CdSrtA as a protein labeling tool and provide insight into the enzyme catalyzed reaction that underpins protein labeling and pilus biogenesis.

A recent update on the use of microbial transglutaminase for the generation of biotherapeutics

The recent scientific progresses on the use of enzyme-mediated reactions in organic, non-aqueous and aqueous media have significantly supported the growing demand of new biotechnological and/or pharmacological products. Today, a plethora of microbial enzymes, used as biocatalysts, are available. Among these, microbial transglutaminases (MTGs) are broadly used for their ability to catalyse the formation of an isopeptide bond between the γ-amide group of glutamines and the ε-amino group of lysine. Due to their promiscuity towards primary amine-containing substrates and the more stringent specificity for glutamine-containing peptide sequences, several combined approaches can be tailored for different settings, making MTGs very attractive catalysts for generating protein-protein and protein small molecule's conjugates. The present review offers a recent update on the modifications attainable by MTG-catalysed bioreactions as reported between 2014 and 2019. In particular, we present a detailed and comparative overview on the MTG-based methods for proteins and antibodies engineering, with a particular outlook on the synthesis of homogeneous antibody-drug conjugates.

Enzymatic labelling of snake venom phospholipase A2 toxins

Almost all animal venoms contain secretory phospholipases A₂ (PLA₂s), 14 kDa disulfide-rich enzymes that hydrolyze membrane phospholipids at the sn-2 position, releasing lysophospholipids and fatty acids. These proteins, depending on their sequence, show a wide variety of biochemical, toxic and pharmacological effects and deserve to be studied for their numerous possible applications, and to improve antivenom drugs. The cellular localization and activity of a protein can be studied by conjugating it with a tag. In this work, we applied an enzymatic labelling method, using Streptomyces mobaraense transglutaminase, on three snake venom PLA₂s: a recombinant neuro- and myotoxic group I PLA₂ from Notechis scutatus scutatus, and two myotoxic group II PLA₂s from Bothrops asper - one of them a natural catalytically inactive variant. We demonstrate that TGase can be used to produce active mono- or bi-derivatives of these three PLA₂s modified at specific Lys residues, and that all three of these proteins, conjugated with fluorescent peptides, are internalized in primary myotubes.