Synergistic effects of microbial transglutaminase and apple pectin on the gelation properties of pea protein isolate and its application to probiotic encapsulation

The low gelation capacity of pea protein isolate (PPI) limits their use in food industry. Therefore, microbial transglutaminase (MTG) and apple pectin (AP) were combined to modify PPI to enhance its gelling characteristics, and the mechanism of MTG-induced PPI-AP composite gel generation was investigated. PPI (10 wt%) could not form a gel at 40 °C, while MTG-treated PPI (10 wt%) formed a self-supporting gel at 40 °C. Subsequently, the addition of AP further promoted the crosslinking of PPI and significantly improved the water holding capacity, rheology, and strength of PPI gels, which was attributed to both hydrogen and isopeptide bonds in the composite gel. Additionally, the PPI-AP composite gel showed excellent protection ability, and the survival rate of probiotics could reach over 90%, which could be used as an effective delivery system. This study verified that MTG and AP were efficient in enhancing the functional quality of PPI gels.

Effect of sanxan as novel natural gel modifier on the physicochemical and structural properties of microbial transglutaminase-induced mung bean protein isolate gels

Mung bean protein isolate (MBPI) has attracted much attention as an emerging plant protein. However, its application was limited by the poor gelling characteristics. Thus, the effect of sanxan (SAN) on the gelling behavior of MBPI under microbial transglutaminase (MTG)-induced condition were explored in this study. The results demonstrated that SAN remarkably enhanced the storage modulus, water-holding capacity and mechanical strength. Furthermore, SAN changed the microstructure of MBPI gels to become more dense and ordered. The results of zeta potential indicated the electrostatic interactions existed between SAN and MBPI. The incorporation of SAN altered the secondary structure and molecular conformation of MBPI, and hydrophobic interactions and hydrogen bonding were necessary to maintain the network structure. Additionally, in vitro digestion simulation results exhibited that SAN remarkably improved the capability of MBPI gels to deliver bioactive substances. These findings provided a practical strategy to use natural SAN to improve legume protein gels.

coli cytoplasm

Microbial transglutaminase (MTG) is a usable enzyme for biomacromolecule modification. In the present study, a "molecular chaperonin" strategy was developed to produce MTG in E. coli cytoplasm with high expression level and a "small molecule-mediated chemical modification" strategy was adopted to strip propeptide chaperonin efficiently during purification. Propeptide (Pro) was expressed separately as a chaperonin to facilitate MTG expression in E. coli cytoplasm with a yield up to 300 mg or about 9 kU from 1 L fed-batch culture. Furthermore, small molecular chemicals were applied to interfere the interaction between MTG and Pro. Chemical acetylation was identified as a suitable method to strip Pro resulting in pure MTG with high specific activity up to 49.6 U/mg. The purified acetylated MTG was characterized by MS analysis. The deconvoluted mass and Peptide Sequence Tags analysis confirmed acetylation on amino groups of MTG protein. Finally, the applications of obtained MTG were demonstrated via protein polymerization of bovine serum albumin and PEGylation of human interferon-α2b. Our method provides MTG with high purity and specific activity as well as unique merit with masked amino groups thus avoiding self-polymerization and cross-linking between MTG and substrates.

Hofmeister anion effects synergize with microbial transglutaminase to enhance the techno-functional properties of pea protein

Pea protein are emerging as the most potential alternative for meat products, but its application was hindered by their weaker gelling properties. Here, the feasibility of combining the Hofmeister anion (CO₃^2-, Citrate^3-, and SO₄^2-) effect with microbial transglutaminase (MTG) cross-linking strategy to improve the techno-functional properties of pea protein was studied. Hofmeister anions or/and MTG treatment of pea protein caused a clear shift in far-UV CD spectra towards β-turn and random coil structures. Furthermore, Hofmeister anion and MTG-induced crosslinking caused a reduction of surface hydrophobicity in contrast with anions-treated. Compared to CO₃^2- and SO₄^2-, Citrate^3- treatment can better improve the efficiency of MTG-crosslinking, as demonstrated by a reduction in free amino group contents and an increase in mean diameter size. Using MTG in combination with Hofmeister anions showed significantly improved foam property and gel hardness as well as decrease gelation temperature of pea protein, specifically Citrate^3- treatment. Thus, this research provides a novel and effective method to improve the effect of MTG-cross-linked pea protein, which will play an essential role in future food production.

Recombinant Streptomyces netropsis transglutaminase expressed in Komagataella phaffii (Pichia pastoris) and applied in plant-based chicken nugget

Transglutaminase (TG, EC 2.3.2.13) is widely used to modify functional properties in food systems, which can catalyze cross-linking reaction of proteins. In this work, microbial transglutaminase (MTG) from Streptomyces netropsis was heterologously expressed in the methylotrophic yeast Komagataella phaffii (Pichia pastoris). The specific activity of recombinant microbial transglutaminase (RMTG) was 26.17 ± 1.26 U/mg, and the optimum pH and temperature were measured as 7.0 and 50 °C, respectively. Bovine serum albumin (BSA) was used as a substrate to evaluate the effect of cross-linking reaction, and we found that RMTG had significant (p < 0.05) cross-linking effect for more than 30 min reactions. RMTG was further utilized in the investigation of plant-based chicken nuggets. Results showed that the hardness, springiness and chewiness of nuggets increased, and the adhesiveness decreased after RMTG treatment, which can prove that RMTG has the potential to improve the texture properties of plant-based chicken nuggets.

One-pot synthesis of fibrillar-shaped functional nanomaterial using microbial transglutaminase

Recently, functional nanowire production using amyloids as a scaffold for protein immobilization has attracted attention. However, protein immobilization on amyloid fibrils often caused protein inactivation. In this study, we investigated protein immobilization using enzymatic peptide ligation to suppress protein inactivation during immobilization. We attempted to immobilize functional molecules such as green fluorescent protein (GFP) and Nanoluc to a transthyretin (TTR) amyloid using microbial transglutaminase (MTG), which links the glutamine side chain to the primary amine. Linkage between amyloid fibrils and functional molecules was achieved through the MTG substrate sequence, and the functional molecules-loaded nanowires were successfully fabricated. We also found that the synthetic process from amyloidization to functional molecules immobilization could be achieved in a single-step procedure.All rights reserved.

Site-specific, covalent immobilization of PNGase F on magnetic particles mediated by microbial transglutaminase

In the workflow of global N-glycosylation analysis, endoglycosidase-mediated removal of glycans from glycoproteins is an essential and rate-limiting step. Peptide-N-glycosidase F (PNGase F) is the most appropriate and efficient endoglycosidase for the removal of N-glycans from glycoproteins prior to analysis. Due to the high demand for PNGase F in both basic and industrial research, convenient and efficient methods are urgently needed to generate PNGase F, preferably in the immobilized form to solid phases. However, there is no integrated approach to implement both efficient expression, and site-specific immobilization of PNGase F. Herein, efficient production of PNGase F with a glutamine tag in Escherichia coli and site-specific covalent immobilization of PNGase F with this special tag via microbial transglutaminase (MTG) is described. PNGase F was fused with a glutamine tag to facilitate the co-expression of proteins in the supernatant. The glutamine tag was covalently and site-specifically transformed to primary amine-containing magnetic particles, mediated by MTG, to immobilize PNGase F. Immobilized PNGase F could deglycosylate substrates with identical enzymatic performance to that of the soluble counterpart, and exhibit good reusability and thermal stability. Moreover, the immobilized PNGase F could also be applied to clinical samples, including serum and saliva.

Mechanically Enhanced Salmo salar Gelatin by Enzymatic Cross-linking: Premise of a Bioinspired Material for Food Packaging, Cosmetics, and Biomedical Applications

Marine animal by-products of the food industry are a great source of valuable biomolecules. Skins and bones are rich in collagen, a protein with various applications in food, cosmetic, healthcare, and medical industries in its native form or partially hydrolyzed (gelatin). Salmon gelatin is a candidate of interest due to its high biomass production available through salmon consumption, its biodegradability, and its high biocompatibility. However, its low mechanical and thermal properties can be an obstacle for various applications requiring cohesive material. Thus, gelatin modification by cross-linking is necessary. Enzymatic cross-linking by microbial transglutaminase (MTG) is preferred to chemical cross-linking to avoid the formation of potentially cytotoxic residues. In this work, the potential of salmon skin gelatin was investigated, in a comparative study with porcine gelatin, and an enzymatic versus chemical cross-linking analysis. For this purpose, the two cross-linking methods were applied to produce three-dimensional, porous, and mechanically reinforced hydrogels and sponges with different MTG ratios (2%, 5%, and 10% w/w gelatin). Their biochemical, rheological, and structural properties were characterized, as well as the stability of the material, including the degree of syneresis and the water-binding capacity. The results showed that gelatin enzymatically cross-linked produced material with high cross-linking densities over 70% of free amines. The MTG addition seemed to play a crucial role, as shown by the increase in mechanical and thermal resistances with the production of a cohesive material stable above 40 °C for at least 7 days and comparable to porcine and chemically cross-linked gelatins. Two prototypes were obtained with similar thermal resistances but different microstructures and viscoelastic properties, due to different formation dynamics of the covalent network. Considering these results, the enzymatically cross-linked salmon gelatin is a relevant candidate as a biopolymer for the production of matrix for a wide range of biotechnological applications such as food packaging, cosmetic patch, wound healing dressing, or tissue substitute.

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.

Expression of Bacillus amyloliquefaciens transglutaminase in recombinant E. coli under the control of a bicistronic plasmid system in DO-stat fed-batch bioreactor cultivations

We studied the expression of Bacillus amyloliquefaciens transglutaminase cloned in Escherichia coli BL21(DE3)pLysS harboring the plasmid pBAD/3C/bTGase, a bicistronic expression system, in bioreactor cultivation. Batch and fed-batch controlled as DO-stat strategies were employed for the production of the recombinant enzyme. In 30 h-batch cultivations using Terrific broth (TB), 6 g/L of biomass and 3.12 U/mg_protein of transglutaminase activity were obtained. DO-stat fed-batch cultivations under the control of oxygen concentration (DO-stat) using TB as medium but fed with glucose allowed the increment in biomass formation (17.5 g/L) and enzyme activity (6.43 U/mg_protein). DO-stat fed-batch using mineral medium (M9) and fed with glucose under the same conditions produced even higher enzymatic activity (9.14 U/mg_protein). The pH effect was investigated, and the best enzymatic activity could be observed at pH 8. In all cultivations, the bicistronic system remained stable, with 100% of plasmid-bearing cells. These results show that E. coli bearing bicistronic plasmid constructs to express recombinant TGase could be cultivated in bioreactors under DO-stat fed-batch using mineral medium and it is a promising strategy in future optimizations to produce this important enzyme.

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.

Cross-linking of carbonic anhydrase and formate dehydrogenase based on amino acid specific recognition: Conversion of carbon dioxide to formic acid

Inspired by the cascades performed in vivo, the assembly of multiple enzymes in vitro has strongly moved into the focus of researchers in the field of biocatalysis. In this study, a new, mild and accurate enzyme cross-linking method is revealed. Microbial transglutaminase (MTG) acts as a "cross-linking medium" by identifying the amide group of the glutamine and the primary amine group of lysine in the artificial peptide tags specifically to form an iso-peptide bond. Here, carbonic anhydrase (CA) and formate dehydrogenase (FDH) with different peptide tags that can be recognized by MTG were linked together to obtain different proportions of cross-linked enzymes for efficient conversion of greenhouse gas carbon dioxide to formic acid. After cross-linking, we obtained "one-to-one" and "one-to-more" cross-linked enzyme aggregates. There is a minor residual loss of the two enzymes, the remaining enzyme activity of CA is more than 93%, and the remaining enzyme activity of FDH is more than 84%. In particular, the overall catalytic efficiency of the cross-linked enzyme is increased by 5.8 times compared with free enzymes and the thermal stability of FDH at different temperatures is improved. The applied strategy demonstrates the potential application of MTG in multi-enzyme assembly and synthetic biology.

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.

Surface functionalization of wool via microbial-transglutaminase and bentonite as bio-nano-mordant to achieve multi objective wool and improve dyeability with madder

Recently, natural dyes have a widening scope in various traditional and advanced applications due to their eco-friendly environment. However, improved dyeability of natural dyes still remains a challenging task. This research was aimed to achieve multi-objective wool with improved dyeability using bio-nano-mordant composed of m-Trans-glutaminase, m-TGase, and bentonite nanoclay. Wool fiber was treated through sonochemical method using different concentrations of m-TGase and bentonite. The surface morphology of wool fabric samples was examined by field emission-scanning electron microscopy (FESEM), and Fourier transform Infrared Radiation (FTIR). Further, wool samples treated at different conditions were applied to madder for dyeability examination. The optimum conditions of color coordinates, color strength, K/S, and washing fastness of madder on treated wool fabric with m-TGase and bentonite, were also examined. The results revealed well-made interactions among m-TGase, bentonite, and wool fibers. In addition, surface morphology was strongly influenced by variations in enzyme concentrations so that extra addition of m-TGase lead to clear damage scales or less cuticle surface in SEM images. Moreover, the results showed that the value of K/S for treated wool samples was better than untreated samples. Indeed, amongst all, 5% concentrations of bio-nano-mordant for m-TGase and bentonite have the most constructive K/S values. Similarly, results of ΔE and antibacterial investigations also confirmed its superiority.

coli by using self-cleavable zymogen with mutated propeptide

Microbial transglutaminase from Streptomyces mobaraensis (MTG) has been widely used in food industry and also in research and medical applications, since it can site-specifically modify proteins by the cross-linking reaction of glutamine residue and the primary amino group. The recombinant expression system of MTG in E. coli provides better accessibility for the researchers and thus can promote further utilization of MTG. Herein, we report production of active and soluble MTG in E. coli by using a chimeric protein of tobacco etch virus (TEV) protease and MTG zymogen. A chimera of TEV protease and MTG zymogen with native propeptide resulted in active MTG contaminated with cleaved propeptide due to the strong interaction between the propeptide and catalytic domain of MTG. Introduction of mutations of K9R and Y11A to the propeptide facilitated dissociation of the cleaved propeptide from the catalytic domain of MTG and active MTG without any contamination of the propeptide was obtained. The specific activity of the active MTG was 22.7 ± 2.6 U/mg. The successful expression and purification of active MTG by using the chimera protein of TEV protease and MTG zymogen with mutations in the propeptide can advance the use of MTG and the researches using MTG mediated cross-linking reactions.

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.

Microbial transglutaminase should be considered as an environmental inducer of celiac disease

Due to the recent interest in food additives that can act as triggering factors in autoimmune diseases including celiac disease (CD), the present letter to the editor expands on the microbial transglutaminase (mTG). It is heavily consumed by a plethora of food processing industries as “glue of proteins” thus improving product’s stability, texture and shelf life. However, more and more information is accumulated lately, questioning its safety. Its cross-linked gliadin complexes are immunogenic in CD. The enzyme increases gliadin uptake, is transported in a trans-epithelial way and deposited below the enterocyte’s line, has anti- phagocytic activity, enhances intestinal permeability and creates luminal resistant isopeptide bonds. No doubt that mTG is beneficial to food industries but a caveat to public health is highly recommended.

Effects of ultrasonic treatment on the gel properties of microbial transglutaminase crosslinked soy, whey and soy-whey proteins

This paper studied the influences of diverse ultrasonic power treatments on the physico-chemical properties of soy-whey mixed protein induced by microbial transglutaminase. Two groups of 15% (m/v) of protein solution-sole protein (as control group) and mixed protein were prepared and processed under different ultrasonic powers for 30 min. After ultrasonic power treatments, gel properties were significantly increased: under 300 W, the gel hardness of mixed protein reached a maximum of 998.9 g, with its water binding capacity scoring a maximum of 87%. According to the analysis of fluorescence emission spectrum, the fluorescence intensity and maximum absorption peak had changed, for different ultrasonic power treatments had exposed more groups. The Fourier Transform Infrared Spectroscopy also suggested that ultrasonic power treatments could change the secondary structure of gel samples. The scanning electron microscope demonstrated that the network structure of mixed protein gel displayed more regular and uniform after ultrasonic treatments.

Production of prebiotic gluten-free bread with red rice flour and different microbial transglutaminase concentrations: modeling, sensory and multivariate data analysis

The aim of this study was to develop gluten-free bread formulated with red rice flour and microbial transglutaminase and prebiotic (inulin). First, the physicochemical analysis of minerals present in red rice flour was performed. Response surface methodology was used to analyze the effects of microbial transglutaminase (MTgase) [0.5; 1.0 and 1.5%] in combination with fermentation time (FT) [60; 80 and 100 min] on the quality parameters of gluten-free bread. Acceptance test was used to evaluate the sensory characteristics of breads together with multivariate analysis of data. The addition of MTgase increased bread volume, hardness and chewiness. However, the cohesiveness and springiness of all breads remained unaffected. The formulation (1.0% MTgase and 80 min FT) presented the best sensory attributes through PCA (principal component analysis) and greater acceptance. Overall, red rice flour, prebiotic and MTgase are promisingly useful ingredients for the production of gluten-free quality bread.

Extracellular production of the recombinant bacterial transglutaminase in Pichia pastoris

Microbial pro-transglutaminase (pro-MTGase) from Streptomyces mobaraensis was expressed in Pichia pastoris (Komagataella phaffii) under the control of constitutive GAP promoter. The single copy of the gene containing clone was grown in shake flasks to determine the optimum conditions for the production of recombinant pro-MTGase. Three temperature (20 °C, 25 °C, 28 °C) and four pH (5, 6, 7, 7.5) values were evaluated at the shake flask level for the extracellular production of pro-MTGase. The highest enzyme activity was obtained with low temperature (20 °C) and high pH (7.5). The maximum yield was 9120 U/L. For the large-scale extracellular production of pro-MTGase, the clone was cultivated in 5 L bioreactor. The fermentation process was carried out at 20 °C, pH 7 and 20% dissolved oxygen for 79 h. The enzyme activity was calculated as 37640 U/L for large-scale production. These results indicate that P. pastoris expression system is very suitable for recombinant MTGase production under the control of the GAP promoter.

Bioengineering of microbial transglutaminase for biomedical applications

Microbial transglutaminase (mTGase) is commonly known in the food industry as meat glue due to its incredible ability to "glue" meat proteins together. Aside from being widely exploited in the meat processing industries, mTGase is also widely applied in other food and textile industries by catalysing the formation of isopeptide bonds between peptides or protein substrates. The advancement of technology has opened up new avenues for mTGase in the field of biomedical engineering. Efforts have been made to study the structural properties of mTGase in order to gain an in-depth understanding of the structure-function relationship. This review highlights the developments in mTGase engineering together with its role in biomedical applications including biomaterial fabrication for tissue engineering and biotherapeutics.

Site-specific, covalent immobilization of an engineered enterokinase onto magnetic nanoparticles through transglutaminase-catalyzed bioconjugation

Enterokinase (EK) is one of the most popular enzymes for the in vitro cleavage of fusion proteins due to its high degree of specificity for the amino-acid sequence (Asp)₄-Lys. Enzyme reusability is desirable for reducing operating costs and facilitating the industrial application of EK. In this work, we report the controlled, site-specific and covalent cross-linking of an engineered EK_LC on amine-modified magnetic nanoparticles (NH₂-MNPs) via microbial transglutaminase-catalyzed bioconjugation for the development of the oriented-immobilized enzyme, namely, EK_LC@NH₂-MNP biocatalyst. Upon the site-specific immobilization, approximately 90% EK_LC enzymatic activity was retained, and the biocatalyst exhibited more than 85% of initial enzymatic activity regardless of storage or reusable stability over a month. The EK_LC@NH₂-MNP biocatalyst was further applied to remove the His tag-(Asp)₄-Lys fusion partner from the His tag-(Asp)₄-Lys-(GLP-1)₃ substrate fusion protein, result suggested the EK_LC@NH₂-MNP possessed remarkable reusability, without a significant decrease of enzymatic activity over 10 cycles (P >  0.05). Supported by the unique properties of MNPs, the proposed EK_LC@NH₂-MNP biocatalyst is expected to promote the economical utilization of enterokinase in fusion protein cleavage.

Tailoring Activity and Selectivity of Microbial Transglutaminase

Microbial transglutaminase (mTG), a protein-glutamine γ-glutamyltransferase from Streptomyces mobaraensis, is an enzyme capable of forming isopeptide bonds between the nearly inert (from the chemical point of view) γ-carboxamides present in the side chain of glutamine residues and primary amines. Its high substrate tolerance, compared to other bond-forming enzymes, makes it a versatile tool for numerous applications including food manufacturing, material science, and biotechnology. Although an mTG-mediated bioconjugation is a well-established technique, some major drawbacks of this approach need to be bypassed, with the poor substrate specificity being among the most essential ones. Especially biopharmaceutical methodologies require high subsite specificity of the utilized biocatalyst, which is often not warranted by mTG. Therefore, access to tailor-made transglutaminases is strongly desired. Herein, we describe a protocol for the generation of mTG libraries based on yeast surface display, which allow for the isolation of mutants with altered properties. Moreover, methods for cloning of respective expression vectors, recombinant expression, and in vitro procession are provided.

Site-Specific Antibody-Drug Conjugation Using Microbial Transglutaminase

Antibody-drug conjugates (ADCs) are a relatively young class of cancer therapeutics that combine the superior selectivity of monoclonal antibodies (mAbs) with the high potency of cytotoxic agents. In the first generation of ADCs, the toxic payload is attached to the mAb via chemical conjugation to endogenous lysine or cysteine residues providing only limited control over site specificity and drug-to-antibody ratio (DAR). The resulting product is a heterogeneous population of different ADC species, each with individual characteristics concerning pharmacokinetics, toxicology, and efficacy. Such diverse ADC mixtures are not only difficult to develop but are potentially also accompanied by a suboptimal therapeutic window. To overcome these limitations, alternative conjugation technologies have been developed that allow the production of tailor-made homogeneous ADCs. Due to its high specificity and robust applicability, microbial transglutaminase (mTG), a protein-glutamine γ-glutamyltransferase isolated from Streptomyces mobaraensis, emerged as a versatile tool for ADC manufacturing. Herein, we report a protocol for the site-specific, mTG-mediated modification of antibodies that allows the production of homogeneous and defined ADCs. Moreover, analytical methods for ADC characterization are provided.

Classification of microbial transglutaminases by evaluation of evolution trees, sequence motifs, secondary structure topology and conservation of potential catalytic residues

Despite the growing interest for microbial transglutaminases (TGases), and the large number of genome sequencing data, there is no deep investigation about structural properties within this family of enzymes in bacteria. We performed a classification of microbial TGases, starting from large-scale analysis of all protein sequences annotated as TGase (more than 8000) in database PFAM. We developed a reiterative procedure based on the construction of several phylogenetic trees and manual selection, and detected five main groups of microbial TGases. Searches for sequence motifs evidenced strong conservation in regions containing potential catalytic residues for some groups. Protein structure modelling has been possible for three of the five groups. Analyses of motifs, structural topologies and potential catalytic sites suggest possible interpretations for function similarities and divergences among groups.

Microbial transglutaminase: A new potential player in celiac disease

Microbial transglutaminase is heavily used in the food processing industries to improve food qualities. Being a protein's glue, by cross-linking it creates neoepitope complexes that are immunogenic and potentially pathogenic in celiac disease. Despite low sequence identity, it imitates functionally its family member, the endogenous tissue transglutaminase, which is the autoantigen of celiac disease. The present comprehensive review highlights the enzyme characteristics, endogenous and exogenous intestinal sources, its cross-talks with gluten and gliadin, its immunogenicity and potential pathogenicity and risks for the gluten induced conditions. If substantiated, it might represent a new environmental inducer of celiac disease. The present findings might affect nutritional product labeling, processed food additive policies and consumer health education.

Current insight and futuristic vistas of microbial transglutaminase in nutraceutical industry

Microbial transglutaminase (MTGase) has become a driving force in the food industry cross-linking the food proteins. MTGase-the nature's molecular glue is recognized to reorient food protein's functional properties without affecting its nutritive value. The scope and approach of this review is to have insight on the action mechanism of MTGase and impact of molecular linkage on functional proteins in various protein moieties in development of innovative features in food production for better consumer's choice and satisfaction. The study covers a wide range of published work across food industries involving innovative use of MTGase, an environment friendly production approach for commercial utilization to get better outcome in terms of culinary delight. The intrinsic biochemical properties and structural information by sequence analysis and clustering validates the mode of reaction mechanism of the biological glue enzyme. The review singles out how the MTGase emerged as a prime choice in ever evolving food industry.

Preparation and characterization of C-phycocyanin peptide grafted N-succinyl chitosan by enzyme method

C‑phycocyanin peptide (CPC) grafted N‑succinyl chitosan (NSC) was prepared via the catalysis of Microbial transglutaminase (MTGase). The single factor experiment displayed that the degree of substitution (DS) of N‑succinyl chitosan‑C‑phycocyanin peptide (NSC‑CPC) depended on the reaction time, the reaction temperature and the reaction pH value. The CS, synthesized NSC and NSC‑CPC were characterized by Fourier transform infrared spectroscopy (FT-IR). NSC‑CPC showed excellent moisture absorption and retention ability. In vitro antioxidant activity assays demonstrated that, with the DS and concentration increasing of NSC‑CPC, the scavenging activity of 1,1‑Diphenyl‑2‑pic‑rylhydrazyl (DPPH) radical and hydroxyl radical increased. The methylthiazol tetrazolium (MTT) essay demonstrated that NSC‑CPC inhibited Hela cells while promoted the proliferation of L929 mouse fibroblasts. In conclusion, these results suggested the potential application of NSC‑CPC in pharmaceutical and biomedical fields.

Mechanically tuned 3 dimensional hydrogels support human mammary fibroblast growth and viability

Background

Carcinoma associated fibroblasts (CAFs or myofibroblasts) are activated fibroblasts which participate in breast tumor growth, angiogenesis, invasion, metastasis and therapy resistance. As such, recent efforts have been directed toward understanding the factors responsible for activation of the phenotype. In this study, we have investigated how changes in the mechanical stiffness of a 3D hydrogel alter the behavior and myofibroblast-like properties of human mammary fibroblasts (HMFs).

Results

Here, we utilized microbial transglutaminase (mTG) to mechanically tune the stiffness of gelatin hydrogels and used rheology to show that increasing concentrations mTG resulted in hydrogels with greater elastic moduli (G’). Upon encapsulation of HMFs in 200 (compliant), 300 (moderate) and 1100 Pa (stiff) mTG hydrogels, it was found that the HMFs remained viable and proliferated over the 7 day culture period. Specifically, rates of proliferation were greatest for HMFs in moderate hydrogels. Regarding morphology, HMFs in compliant and moderate hydrogels exhibited a spindle-like morphology while HMFs in stiff hydrogels exhibited a rounded morphology with several large cellular protrusions. Quantification of cell morphology revealed that HMFs cultured in all mTG hydrogels overall assumed a more elongated phenotype over time in culture; however, few significant differences in morphology were observed between HMFs in each of the hydrogel conditions. To determine whether matrix stiffness upregulated expression of ECM and myofibroblast markers, western blot was performed on HMFs in compliant, moderate and stiff hydrogels. It was found that ECM and myofibroblast proteins varied in expression during both the culture period and according to matrix stiffness with no clear correlation between matrix stiffness and a myofibroblast phenotype. Finally, TGF-β levels were quantified in the conditioned media from HMFs in compliant, moderate and stiff hydrogels. TGF-β was significantly greater for HMFs encapsulated in stiff hydrogels.

Conclusions

Overall, these results show that while HMFs are viable and proliferate in mTG hydrogels, increasing matrix stiffness of mTG gelatin hydrogels doesn’t support a robust myofibroblast phenotype from HMFs. These results have important implications for further understanding how modulating 3D matrix stiffness affects fibroblast morphology and activation into a myofibroblast phenotype.

Electronic supplementary material

The online version of this article (10.1186/s12860-017-0151-y) contains supplementary material, which is available to authorized users.

Molecular interaction mechanisms in reverse micellar extraction of microbial transglutaminase

Reverse micellar extraction is an efficient and economical alternative for protein purification. In this study, microbial transglutaminase (MTGase) from crude materials was purified using reverse micellar extraction, and the molecular interaction mechanism in reverse micellar extraction of MTGase was explored. By using a molecular simulation study, the interaction mechanism of forward extraction was investigated. The molecular simulation results reveal the interaction of MTGase-water-surfactant is the major driving force for the forward extraction. Further, the effect of ionic strength on molecular interactions in backward extraction was investigated using 1H low-field nuclear magnetic resonance (LF-NMR) and circular dichroism (CD) spectra. In backward extraction, the interactions between water and the other two molecules (MTGase and surfactant molecules) are enhanced while the interactions between target molecules (MTGase) and the other two molecules (water and surfactant molecules) are weakened as the ionic strength increases. Moreover, the effect of size exclusion on backward extraction was also investigated. The results demonstrate size exclusion has limit effect at high ionic strength, and the weakened interaction of MTGase-water-surfactant is the main reason causing the release of the target molecules in backward extraction. This work might provide valuable reference to the MTGase purification and downstream processing.

Optimization of low-fat set-type yoghurt: effect of altered whey protein to casein ratio, fat content and microbial transglutaminase on rheological and sensorial properties

In the present study the amount of whey protein to casein ratio (W/C ratio) (0.22-0.7), fat content (FC) (0.5-1.5%) and microbial transglutaminase (mTGase) (0.0-1.0 U/g substrate protein) in the formulation of low fat set type yoghurt, prepared from reconstituted milk, were optimized by response surface method to achieve the best rheological properties and sensory characteristics. The selected parameters consisted of higher consistency coefficient, consistency, texture and mouth feeling and lower syneresis and pH. The optimum condition was found to be 0.97, 0.46 and 0.5% of the enzyme concentration, W/C ratio and FC respectively. Results showed that thermal denaturation increased up to 33% with increasing W/C ratio significantly. All samples showed non-Newtonian shear thinning behavior. Increasing in W/C ratio from 0.22 to 0.7 raised the consistency coefficient, yield stress and textural parameters such as hardness and consistency of yoghurt. Enzyme addition (together with starter culture addition) increased yoghurt viscosity and yield stress. In sensory evaluation W/C ratio affected the texture and mouth feeling of yoghurt samples and the influences of FC and mTGase were not significant. Yoghurt syneresis was highly affected by FC, W/C ratio and mTGase.

Comparison of rheological behaviors and nanostructure of bighead carp scales gelatin modified by different modification methods

In this study, microbial transglutaminase (MTGase) and pectin were compared to modify bighead carp (Hypophthalmichthys nobilis) scale gelatin. The functional properties of modified fish scales gelatin (FSG) were largely improved, including melting temperature and rheological behavior. While, modification methods decreased the triple-helix content and destroyed the single left-hand helix chain of modified FSG as investigated by X-ray diffraction. MTGase could induce the denser and finer gels network, but had none significant effect on nanostructural properties of fish gelatin. Pectin inserted itself into the fish gelatin gels network and caused aggregations, forming crystalline peaks and various nanostructures. In particular, compared with pectin modified FSG, MTGase produced FSG with lower storage modulus and apparent viscosity, but higher gel points and melting points.

Physico-chemical, microstructural and rheological properties of camel-milk yogurt as enhanced by microbial transglutaminase

Camel milk produces watery texture when it is processed to yogurt. Despite the extensive studies on microbial transglutaminase (MTGase) in dairy research, the effect of this enzyme on the properties of yogurt made from camel milk has not been studied. This study aims to investigate the impact of MTGase with and without bovine skimmed milk powder (SMP), whey protein concentrate (WPC),or β-lactoglobulin (β-lg) on physico-chemical, rheological, microstructural, and sensory properties of camel-milk yogurt during 15 days of storage period. MTGase treatment markedly reduced the fermentation time of unfortified and SMP-fortified camel milk. The fortification of camel milk without MTGase failed to give set-type yogurt. The treatment of unfortified milk with MTGase enormously improved the viscosity and the body of yogurt samples. Fortification of MTGase-treated milk impacted positively on the viscosity, the water holding capacity, and the density of the protein matrix in the gel microstructure, which were influenced by the type of dairy ingredients. All MTGase-treated yogurts differed from each other in hardness and adhesiveness values. Electrophoresis results showed that the susceptibility of the individual milk proteins to MTGase varied, and there were differences among the treatments toward the enzyme. SMP-fortified yogurt was the most accepted product. Generally, the addition of MTGase preparation at a concentration of 0.4%, simultaneously with starter culture, to fortified camel milk was considered an effective tool to solve the challenges of producing set-type yogurt from this milk.

The effects of modified versus unmodified wheat gluten administration in patients with celiac disease

Celiac disease (CD) treatment requires a gluten-free diet (GFD), although alternative approaches have been proposed. Modification of gliadin peptides using microbial transglutaminase (mTG) inhibits their ability to induce immune response in vitro. Our aim was to evaluate the safety of mTG-modified wheat flour ingestion in CD patients. Twenty-one CD patients in remission were randomized to receive mTG-modified (n=11) or unmodified (n=10) wheat flour rusks, in double-blind fashion. Monthly, patients completed a symptom questionnaire. Serum anti-tTG, EMA and creatinine levels were monitored. At baseline and after 90days, serum anti-actin antibodies (AAA) were measured and upper endoscopy was performed. Data were analyzed by non-parametric tests. 7/11 patients eating modified rusks and 7/10 patients receiving unmodified rusks completed the study. At baseline, all patients showed negative serum anti-tTG and EMA results. At the end, 2/7 (28.6%) patients ingesting modified and 4/7 (57.1%) patients taking unmodified rusks presented positive serum anti-tTG and EMA results. Creatinine results were unmodified. Moreover, 1/7 (14.3%) patients ingesting modified and 4/7 (57.1%) patients taking unmodified rusks presented villous atrophy. In patients who received unmodified rusks, the AAA levels increased significantly and duodenal anti-tTG levels appeared higher than those measured in patients who ate modified rusks. Abdominal swelling, bloating and nausea were more severe in patients ingesting unmodified rusks than those taking modified rusks. Our results may support larger clinical trials to confirm the enzymatic treatment of wheat flour as an alternative to GFD. Clinicaltrials.gov registration no: NCT02472119.

Constitutive expression of active microbial transglutaminase in Escherichia coli and comparative characterization to a known variant

Background

Microbial transglutaminase (mTG) is a robust enzyme catalyzing the formation of an isopeptide bond between glutamine and lysine residues. It has found use in food applications, pharmaceuticals, textiles, and biomedicine. Overexpression of soluble and active mTG in E. coli has been limited due to improper protein folding and requirement for proteolytic cleavage of the pro-domain. Furthermore, to integrate mTG more fully industrially and academically, thermostable and solvent-stable variants may be imperative.

Results

A novel expression system constitutively producing active mTG was designed. Wild-type (WT) mTG and a S2P variant had similar expression levels, comparable to previous studies. Kinetic constants were determined by a glutamate dehydrogenase-coupled assay, and the S2P variant showed an increased affinity and a doubled enzyme efficiency towards Z-Gln-Gly. The melting temperature (T_m) of the WT was determined by intrinsic fluorescence measurements to be 55.8 ± 0.1 °C and of the S2P variant to be 56.3 ± 0.4 °C and 45.5 ± 0.1 °C, showing a moderately different thermostability profile. Stability in water miscible organic solvents was determined for both the WT and S2P variant. Of the solvents tested, incubation of mTG in isopropanol for 24 h at 4 °C showed the strongest stabilizing effect with mTG retaining 61 and 72% activity for WT and S2P respectively in 70% isopropanol. Both enzymes also showed an increased initial activity in the presence of organic solvents with the highest activity increase in 40% DMSO. Nevertheless, both enzymes were inactivated in 70% of all organic solvents tested.

Conclusions

A constitutive expression system of active mTG in E. coli without downstream proteolytic cleavage processing was used for overexpression and characterization. High throughput techniques for testing thermostability and kinetics were useful in streamlining analysis and could be used in the future for quickly identifying beneficial mutants. Hitherto untested thermostability and stability of mTG in organic solvents was evaluated, which can pave the way for use of the enzyme in novel applications and processes.

Effects of microbial transglutaminase, fibrimex and alginate on physicochemical properties of cooked ground meat with reduced salt level

Effects of microbial transglutaminase (MTGase), fibrin/thrombin combination (fibrimex), alginate or combination of these binding agents on physicochemical parameters of cooked ground beef with reduced salt level were investigated. Seventeen treatments included three control (no binding agent) groups incorporated with varying concentrations of salt (0.5, 1, 2%, w/w) and fourteen treatment groups produced with MTGase or fibrimex or alginate or their combinations at 0.5 or 1% salt levels. The samples were analyzed for cooking loss (CL), pH, color, moisture, fat, protein, ash, salt, texture and TBARS. The results indicated that the use of MTGase or fibrimex or MTGase/fibrimex combination had significant effect on preventing textural deterioration caused by salt reduction. Even though the use of MTGase resulted in higher CL values, formulation of ground beef with fibrimex or alginate or MTGase/fibrimex/alginate combinations reduced CL when compared with the control groups. The use of fibrimex in ground beef resulted in a decrease in TBARS, lightness, redness and pH values. However, the use of alginate caused an increase in pH, lightness and redness values of ground beef. Based on the present study, the use of fibrimex or a combination of fibrimex with MTGase in the product formulation can be an effective strategy to reduce cooking loss, to improve or maintain the textural properties and to extend shelf life of cooked ground beef with reduced salt level.

[THREE-DIMENSIONAL CULTURED ADIPOSE-DERIVED STEM CELLS BASED ON MICROBIAL TRANSGLUTAMINASE ENZYME CROSSLINKED GELATIN HYDROGEL]

OBJECTIVE

To study the growth of adipose-derived stem cells (ADSCs) planted in three-dimensional (3D) materials, a 3D cultured ADSCs system based on microbial transglutaminase (mTG) enzyme crosslinked gelatin hydrogel was constructed.

METHODS

ADSCs were isolated from the subcutaneous adipose tissue of a Sprague Dawley rat by collagenase digestion and centrifugation, and were cultured for passage. The mTG enzyme crosslinked gelatin hydrogel was firstly synthesized by mixing gelatin and mTG, and then the ADSCs were encapsulated in situ (2D environment) and cultured in the 3D materials (3D environment). The morphology and adhesion of cells were observed by inverted phase contrast microscope. In addition, HE staining and Masson staining were carried out to observe the distribution of cells in the material. Living and death situation of ADSCs in the materials was observed by fluorescence microscope and laser scanning confocal microscopy. Scanning electron microscopy was used to observe the adhesion of ADSCs on hydrogel surface. Alamar-Blue method was used to detect the proliferation of ADSCs in the hydrogel. Moreover, the results were compared between the cells cultured in 2D environment and those in 3D environment.

RESULTS

The result of 2D culture showed that ADSCs grew well on the hydrogel surface with normal functioning and had good adhesion. The results of 3D culture showed that ADSCs grew well in 3D cultured mTG enzyme crosslinked gelatin hydrogel, and presented 3D shape. Cells obviously extended in all directions. The number of apoptotic cells was very small. The cells of 3D culture at each time point was significantly less than that of the conventional culture cells, difference was statistically significant (P<0.05). But after 8 days culture, the proliferation of the cells cultured in the mTG enzyme crosslinked gelatin hydrogel increased more quickly.

CONCLUSIONS

ADSCs can grow well with good adhesion and show high viability in 3D culture system constructed by mTG enzyme crosslinked gelatin hydrogel.

The industrial food additive, microbial transglutaminase, mimics tissue transglutaminase and is immunogenic in celiac disease patients

Microbial transglutaminase (mTg) is capable of cross-linking numerous molecules. It is a family member of human tissue transglutaminase (tTg), and is involved in CD. Despite declarations of the safety of mTg for industrial use, direct evidence for immunogenicity of the enzyme is lacking. The serological activity of mTg, tTg, gliadin complexed mTg (mTg neo-epitope) and gliadin complexed tTg (tTg neo-epitope) were studied in 95 pediatric celiac patients (CD), 99 normal children (NC), 79 normal adults (NA) and 45 children with nonspecific abdominal pain (AP). Sera were tested by ELISAs, detecting IgA, IgG or both IgA and IgG (check): AESKULISA® tTg (tTg), AESKULISA® tTg New Generation (tTg neo-epitope (tTg-neo)), microbial transglutaminase (mTg) and mTg neo-epitope (mTg-neo). Marsh criteria were used for the degree of intestinal injury. Parallel, mTg and tTg neo-epitopes were purified by asymmetric field flow fractionation, confirmed by multi-light-scattering and SDS-PAGE, and analyzed in adult CD and control groups by competition ELISAs. No sequence homology but active site similarity were detected on alignment of the 2 Tgs. Comparing pediatric CD patients with the 2 normal groups: mTg-neo IgA, IgG and IgA+IgG antibody activities exceed the comparable mTg ones (p<0.0001). All mTg-neo and tTg-neo levels were higher (p<0.001). tTg IgA and IgG+IgA were higher than mTg IgA and IgA+IgG (p<0.0001). The levels of tTg-neo IgA/IgG were higher than tTg IgA/IgG (p<0.0001). The sequential antibody activities best reflecting the increased intestinal damage were tTg-neo check>tTg-neo IgA≥mTg-neo IgG>tTg-neo IgG>mTg-neo check>mTg-neo IgA. Taken together, tTg-neo check, tTg-neo IgA and mTg-neo IgG correlated best with intestinal pathology (r²=0.6454, r²=0.6165, r²=0.5633; p<0.0001, p<0.0001, p<0.0001, respectively). Purified mTg-neo IgG and IgA showed an increased immunoreactivity compared to single mTg and gliadin (p<0.001) but similar immunoreactivity to the tTg-neo IgG and IgA ELISA. Using competition ELISA, the mTg neo-epitopes and tTg neo-epitopes have identical outcomes in CD sera both showing a decrease in optical density of 55±6% (p<0.0002). mTg is immunogenic in children with CD and, by complexing to gliadin, its immunogenicity is enhanced. Anti-mTg-neo-epitope IgG antibodies correlate with intestinal damage to a comparable degree as anti-tTg-neo IgA. mTg and tTg display a comparable immunopotent epitope. mTg-neo IgG is a new marker for CD. Further studies are needed to explore the pathogenic potential of anti-mTg antibodies in CD.

Site-specific, covalent immobilization of BirA by microbial transglutaminase: A reusable biocatalyst for in vitro biotinylation

A facile approach for the production of a reusable immobilized recombinant Escherichia coli biotin ligase (BirA) onto amine-modified magnetic microspheres (MMS) via covalent cross-linking catalyzed using microbial transglutaminase (MTG) was proposed in this study. The site-specifically immobilized BirA exhibited approximately 95% of enzymatic activity of the free BirA, and without a significant loss in intrinsic activity after 10 rounds of recycling (P > 0.05). In addition, the immobilized BirA can be easily recovered from the solution via a simple magnetic separation. Thus, the immobilized BirA may be of general use for in vitro biotinylation in an efficient and economical manner.

Transglutaminase-induced gelation properties of soy protein isolate and wheat gluten mixtures with high intensity ultrasonic pretreatment

Soy protein isolate (SPI) and wheat gluten (WG) are widely used in commercial food applications in Asia for their nutritional value and functional properties. However, individually each exhibits poor gelation. In this study, we examined the microbial transglutaminase (MTGase)-induced gelation properties of SPI and WG mixtures with high intensity ultrasonic pretreatment. Ultrasonic treatment reduced the particle size of SPI/WG molecules, which led to improvements in surface hydrophobicity (Ho) and free sulfhydryl (SH) group content. However, MTGase crosslinking facilitated the formation of disulfide bonds, markedly decreasing the content of free SH groups. Ultrasonic treatment improved the gel strength, water holding capacity, and storage modulus and resulted in denser and more homogeneous networks of MTGase-induced SPI/WG gels. In addition, ultrasonic treatment changed the secondary structure of the gel samples as determined by Fourier transform infrared spectroscopic analysis, with a reduction in α-helices and β-turns and an increase in β-sheets and random coils. Thus, ultrasound is useful in facilitating the gelation properties of MTGase-induced SPI/WG gels and might expand their utilization in the food protein gelation industry.

Enzymatic conjugation of multiple proteins on a DNA aptamer in a tail-specific manner

Conjugation of single-strand DNA aptamers and enzymes has been of great significance in bioanalytical and biomedical applications because of the unlimited functions provided by DNA aptamer direction. Therefore, we developed efficient tailing of a DNA aptamer, with end-specific conjugation of multiple enzymes, through enzymatic catalysis. Terminal deoxynucleotidyl transferase (TdT) added multiple Z-Gln-Gly (Z-QG) moieties to the 3'-end of a DNA aptamer via the addition of Z-QG-modified deoxyuridine triphosphate (Z-QG-dUTP) and deoxynucleoside triphosphates (dNTPs). The resultant (Z-QG)m -(dN)l-aptamer, whose Z-QGs with dN spacers served as stickers for microbial transglutaminase (MTG), were crosslinked between the Z-QGs on the DNA and a substrate peptide sequence containing lysine (K), fused to a recombinant enzyme (i.e. bacterial alkaline phosphatase; BAP) by MTG. The incorporation efficiency of Z-QG moieties on the aptamer tail and the subsequent conjugation efficiency with multiple enzyme molecules were dramatically altered by the presence of dNTPs, revealing that a combination of Z-QG-dUTP/dTTP comprised the best labeling efficiency and corresponding properties during analytical performance. Thus, a novel optimized platform for designing (BAP)n -(dT)l-DNA aptamers was demonstrated for the first time in this article, offering unique opportunities for tailoring new types of covalent protein-nucleic acid conjugates in a controllable way.

The microbial transglutaminase immobilization on carboxylated poly(N-isopropylacrylamide) for thermo-responsivity

Microbial transglutaminase (mTG) is widely utilized in the PEGylation of pharmaceutical proteins. mTG immobilization can be achieved via covalent bonding on solid supports. However, the catalytic efficiency of mTG immobilized on solid supports was significantly reduced by mass transfer limitation. To overcome this limitation, mTG was covalently immobilized on the thermo-responsive carboxylated poly(N-isopropylacrylamide) (pNIPAM). The pNIPAM-mTG conjugate exhibited reversibly solubility in aqueous solution with a low critical solution temperature (LCST) at 39°C, i.e., it was insoluble above 39°C and soluble below 39°C. The pH dependence of the pNIPAM-mTG conjugate was similar with that of the native mTG. Upon conjugation to pNIPAM, the optimal temperature of mTG shifted down from 50-55°C to 40-45°C, and the thermal stability of the conjugate was elevated. The easy separation of the pNIPAM-mTG conjugate with its substrate and the catalytic efficiency of the pNIPAM-mTG conjugate were demonstrated by employing the pNIPAM-mTG conjugate to cross-link bovine serum albumin (BSA) and catalyze PEGylation of therapeutic protein, cytochrome c (Cyt C), respectively. The thermo-responsive mTG is suitable to modify proteins in food processing and biomedical engineering.

Size measuring techniques as tool to monitor pea proteins intramolecular crosslinking by transglutaminase treatment

In this work, techniques for monitoring the intramolecular transglutaminase cross-links of pea proteins, based on protein size determination, were developed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of transglutaminase-treated low concentration (0.01% w/w) pea albumin samples, compared to the untreated one (control), showed a higher electrophoretic migration of the major albumin fraction band (26 kDa), reflecting a decrease in protein size. This protein size decrease was confirmed, after DEAE column purification, by dynamic light scattering (DLS) where the hydrodynamic radius of treated samples appears to be reduced compared to the control one.

Effect of transglutaminase on quality characteristics of a value-added product tilapia wastes

The aim of this work was to evaluate the physico-chemical, instrumental color and texture, and sensory qualities of restructured tilapia steaks elaborated with small sized (non-commercial) tilapia fillets and different levels of microbial transglutaminase (MTG). Four concentrations of MTG were used: CON (0 % MTG), T1 (0.1 % MTG), T2 (0.5 % MTG), and T3 (0.8 % MTG). In addition, bacterial content and pH shifts were also evaluated during 90 days of frozen storage. The different levels of MTG did not affect (P > 0.05) either the proximate composition of the restructured tilapia steaks or the bacterial growth during the frozen storage. MTG improved (P < 0.05) cooking yield and instrumental hardness and chewiness as well as sensory (salty taste, succulence and tenderness) attributes; strongly contributing to greater overall acceptance. Therefore, restructured tilapia steaks manufactured with MTG are potentially valued-added products with good consumer acceptance and better purchase-intention than steaks formulated with 0 % MTG.

Biochemical modifications of gliadins induced by microbial transglutaminase on wheat flour

BACKGROUND

Celiac disease (CD) is an immune-mediated disorder caused by the ingestion of wheat gluten. A lifelong, gluten-free diet is required to normalize the intestinal mucosa. We previously found that transamidation by microbial transglutaminase (mTGase) suppressed the gliadin-specific immune response in intestinal T-cell lines from CD patients and in models of gluten sensitivity.

METHODS

SDS-PAGE, Western blot, ELISA, tissue transglutaminase (tTGase) assay and nano-HPLC-ESI-MS/MS experiments were used to analyze prolamins isolated from treated wheat flour.

RESULTS

Gliadin and glutenin yields decreased to 7.6±0.5% and 7.5±0.3%, respectively, after a two-step transamidation reaction that produced a water-soluble protein fraction (spf). SDS-PAGE, Western blot and ELISA analyses confirmed the loss of immune cross-reactivity with anti-native gliadin antibodies in residual transamidated gliadins (K-gliadins) and spf as well as the occurrence of neo-epitopes. Nano-HPLC-ESI-MS/MS experiments identified some native and transamidated forms of celiacogenic peptides including p31-49 and confirmed that mTGase had similar stereo-specificity of tTGase. Those peptides resulted to be 100% and 57% modified in spf and K-gliadins, respectively. In particular, following transamidation p31-49 lost its ability to increase tTGase activity in Caco-2 cells. Finally, bread manufactured with transamidated flour had only minor changes in baking characteristics.

CONCLUSIONS

The two-step transamidation reaction modified the analyzed gliadin peptides, which are known to trigger CD, without influencing main technological properties.

GENERAL SIGNIFICANCE

Our data shed further light on a detoxification strategy alternative to the gluten free diet and may have important implications for the management of CD patients.

Tailing DNA aptamers with a functional protein by two-step enzymatic reaction

An efficient, quantitative synthetic strategy for aptamer-enzyme conjugates was developed by using a two-step enzymatic reaction. Terminal deoxynucleotidyl transferase (TdT) was used to first incorporate a Z-Gln-Gly (QG) modified nucleotide which can act as a glutamine donor for a subsequent enzymatic reaction, to the 3'-OH of a DNA aptamer. Microbial transglutaminase (MTG) then catalyzed the cross-linking between the Z-QG modified aptamers and an enzyme tagged with an MTG-reactive lysine containing peptide. The use of a Z-QG modified dideoxynucleotide (Z-QG-ddUTP) or a deoxyuridine triphosphate (Z-QG-dUTP) in the TdT reaction enables the controlled introduction of a single or multiple MTG reactive residues. This leads to the preparation of enzyme-aptamer and (enzyme)n-aptamer conjugates with different detection limits of thrombin, a model analyte, in a sandwich enzyme-linked aptamer assay (ELAA). Since the combination of two enzymatic reactions yields high site-specificity and requires only short peptide substrates, the methodology should be useful for the labeling of DNA/RNA aptamers with proteins.