The LQSP tetrapeptide is a new highly efficient substrate of microbial transglutaminase for the site-specific derivatization of peptides and proteins

Adapting Ferritin, a Naturally Occurring Protein Cage, to Modulate Intrinsic Agonism of OX40

Ferritin is a multivalent, self-assembling protein scaffold found in most human cell types, in addition to being present in invertebrates, higher plants, fungi, and bacteria, that offers an attractive alternative to polymer-based drug delivery systems (DDS). In this study, the utility of the ferritin cage as a DDS was demonstrated within the context of T cell agonism for tumor killing. Members of the tumor necrosis factor receptor superfamily (TNFRSF) are attractive targets for the development of anticancer therapeutics. These receptors are endogenously activated by trimeric ligands that occur in transmembrane or soluble forms, and oligomerization and cell-surface anchoring have been shown to be essential aspects of the targeted agonism of this receptor class. Here, we demonstrated that the ferritin cage could be easily tailored for multivalent display of anti-OX40 antibody fragments on its surface and determined that these arrays are capable of pathway activation through cell-surface clustering. Together, these results confirm the utility, versatility, and developability of ferritin as a DDS.

Recombinant humanized Fab fragments targeting the CFC domain of human Cripto-1

In the era of immunotherapy, the targeting of disease-specific biomarkers goes hand in hand with the development of highly selective antibody-based reagents having optimal pharmacological/toxicological profiles. One interesting and debated biomaker for several types of cancers is the onco-fetal protein Cripto-1 that is selectively expressed in many solid tumours and has been actively investigated as potential theranostic target. Starting from previously described anti-CFC/Cripto-1 murine monoclonal antibodies, we have moved forward to prepare the humanized recombinant Fabs which have been engineered so as to bear an MTGase site useful for a one-step site-specific labelling. The purified and bioconjugated molecules have been extensively characterized and tested on Cripto-1-positive cancer cells through in vitro binding assays. These recombinant Fab fragments recognize the target antigen in its native form on intact cells suggesting that they can be further developed as reagents for detecting Cripto-1 in theranostic settings.

Production in Bacteria and Characterization of Engineered Humanized Fab Fragment against the Nodal Protein

Drug development in recent years is increasingly focused on developing personalized treatments based on blocking molecules selective for therapeutic targets specifically present in individual patients. In this perspective, the specificity of therapeutic targets and blocking agents plays a crucial role. Monoclonal antibodies (mAbs) and their surrogates are increasingly used in this context thanks to their ability to bind therapeutic targets and to inhibit their activity or to transport bioactive molecules into the compartments in which the targets are expressed. Small antibody-like molecules, such as Fabs, are often used in certain clinical settings where small size and better tissue penetration are required. In the wake of this research trend, we developed a murine mAb (3D1) neutralizing the activity of Nodal, an oncofetal protein that is attracting an ever-increasing interest as a selective therapeutic target for several cancer types. Here, we report the preparation of a recombinant Fab of 3D1 that has been humanized through a computational approach starting from the sequence of the murine antibody. The Fab has been expressed in bacterial cells (1 mg/L bacterial culture), biochemically characterized in terms of stability and binding properties by circular dichroism and bio-layer interferometry techniques and tested in vitro on Nodal-positive cancer cells.

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.

Design of highly active substrates using molecular docking for microbial transglutaminase detection

The transglutaminase (TGase) family catalyzes a transamidation reaction between glutamine (Gln) and lysine (Lys) residues on protein substrates. Highly active substrates are important for cross-linking and modifying proteins of TGase. In the present work, high-activity substrates have been designed based on the principles of enzyme-substrate interaction, using microbial transglutaminase (mTGase) as a research model of the TGase family. Substrates with high activity were screened using a combination of molecular docking and traditional experiments. Twenty-four sets of peptide substrates all produced good catalytic activity with mTGase. FFKKAYAV as the acyl acceptor and VLQRAY as the acyl donor group had the best reaction efficiency with highly sensitive detection of 26 nM mTGase. In addition, the substrate grouping, KAYAV and AFQSAY, detected 130 nM mTGase under physiological conditions (37 °C, pH 7.4), producing 20-fold higher activity than the natural substrate, collagen. The experimental results confirmed the potential for design of high-activity substrates by a combination of molecular docking and traditional experiments under physiological conditions.

Approaching transglutaminase from Streptomyces bacteria over three decades

Transglutaminases are protein cross-linking and protein-modifying enzymes that have attracted considerable interest due to their causal involvement in various diseases and versatility in industrial applications. In particular, microbial transglutaminases (MTG) from Streptomyces bacteria have managed in recent years to evolve from simple food additives to specialized enzymes for the site-directed modification of therapeutic proteins. The review summarizes relevant studies from the beginning dealing with the occurrence, production, structure, catalysis, and substrate molecules of MTG enzymes. It also addresses biotechnological procedures with MTG from S. mobaraensis (SmMTG) as the most prominent representative in focus. Reassessment of the available data revealed unexpected insights into catalysis of SmMTG and other transglutaminases, suggesting selection of glutamine donor proteins by subsites at the front vestibule and the existence of distinct lysine pockets. Flexibility of the SmMTG-accessible glutamine donor substrate regions seems to be more important than the glutamine environment. Nevertheless, residues in close vicinity to glutamines also determine interaction with the SmMTG subsites. The apparent lack of subsites for lysine donor proteins suggests self-assembly of the substrate proteins prior to enzymatic cross-linking. The study of natural substrate proteins, especially their mutual interaction, is proposed to further illuminate catalysis of SmMTG. To this end, structure and function of the characterized substrate proteins from S. mobaraensis are discussed in conclusion.

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.

Generation and testing of engineered multimeric Fabs of trastuzumab

Recombinant antibodies fragments in several new formats are routinely investigated and used in diagnostic and therapeutic applications as anti-cancers molecules. New antibody formats are generated to compensate the need for multispecificity and site-specific introduction of fluorescent dyes, cytotoxic payloads or for generating semisynthetic multimeric molecules. Fabs of trastuzumab bearing transglutaminase (MTG) reactive sites were generated by periplasmic expression in E. coli and purified. Multimeric Fabs were generated by either disulfide bridge formation or by using MTG-sensitive peptide linkers. Binding to receptor was assessed by ELISA and SPR methods. Internalization and growth inhibition assays were performed on BT-474 and SKBR3 Her2+ cells. Fabs were successfully produced and dimerized or trimerized using MTG and suitably designed peptide linkers. Site-specific derivatizations with fluorophores were similarly achieved. The monomeric, dimeric and trimeric variants bind the receptor with affinities similar or superior to the full antibody. Fab and Fab2 are rapidly internalized in Her2+ cells and exhibit growth inhibition abilities similar to the full antibody. Altogether, the data show that the recombinant Fabs can be produced in E. coli and converted into multimeric variants by MTG-based bioconjugation. Similar approaches are extendable to the introduction of cytotoxic payloads for the generation of novel Antibody Drug Conjugates.

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 for biotechnological and biomedical engineering

Research on bacterial transglutaminase dates back to 1989, when the enzyme has been isolated from Streptomyces mobaraensis. Initially discovered during an extensive screening campaign to reduce costs in food manufacturing, it quickly appeared as a robust and versatile tool for biotechnological and pharmaceutical applications due to its excellent activity and simple handling. While pioneering attempts to make use of its extraordinary cross-linking ability resulted in heterogeneous polymers, currently it is applied to site-specifically ligate diverse biomolecules yielding precisely modified hybrid constructs comprising two or more components. This review covers the extensive and rapidly growing field of microbial transglutaminase-mediated bioconjugation with the focus on pharmaceutical research. In addition, engineering of the enzyme by directed evolution and rational design is highlighted. Moreover, cumbersome drawbacks of this technique mainly caused by the enzyme's substrate indiscrimination are discussed as well as the ways to bypass these limitations.

A comparative analysis of catalytic activity and stability of microbial transglutaminase in controlled denaturing conditions

Microbial transglutaminases (MTGs) catalyzes the formation of Gln-Lys isopeptide bonds and are widely used for the cross-linking of proteins and peptides in food and in biotechnological applications for bioconjugation reactions. In view of its practical utility, a comparative study of the catalytic activity and stability of the enzyme in a wide range of denaturing conditions has been performed through Circular Dichroism (CD), fluorescence and activity assays performed with model substrates. In agreement with previous results, we show that MTG has a significant structural and functional tolerance to pH changes, whereas the enzyme stability and activity decrease in presence of increasing amounts of denaturing agents, such as urea and guanidinium chloride (GdnHCl). Noteworthy, the activity of MTG in denaturing conditions differs markedly from that in pseudo-physiological settings, shifting unexpectedly toward higher substrate specificity. Also, the use of controlled amounts of denaturing agents (1.0-1.5 M urea) largely improves yields and purity of the final products of 10-15% and 25-30%, respectively. These findings widen the range of applicability of the MTG-mediated biocatalysis for industrial and biotechnological purposes.

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.

Biocatalysis by Transglutaminases: A Review of Biotechnological Applications

The biocatalytic activity of transglutaminases (TGs) leads to the synthesis of new covalent isopeptide bonds (crosslinks) between peptide-bound glutamine and lysine residues, but also the transamidation of primary amines to glutamine residues, which ultimately can result into protein polymerisation. Operating with a cysteine/histidine/aspartic acid (Cys/His/Asp) catalytic triad, TGs induce the post-translational modification of proteins at both physiological and pathological conditions (e.g., accumulation of matrices in tissue fibrosis). Because of the disparate biotechnological applications, this large family of protein-remodelling enzymes have stimulated an escalation of interest. In the past 50 years, both mammalian and microbial TGs polymerising activity has been exploited in the food industry for the improvement of aliments' quality, texture, and nutritive value, other than to enhance the food appearance and increased marketability. At the same time, the ability of TGs to crosslink extracellular matrix proteins, like collagen, as well as synthetic biopolymers, has led to multiple applications in biomedicine, such as the production of biocompatible scaffolds and hydrogels for tissue engineering and drug delivery, or DNA-protein bio-conjugation and antibody functionalisation. Here, we summarise the most recent advances in the field, focusing on the utilisation of TGs-mediated protein multimerisation in biotechnological and bioengineering applications.

Structural insights into the interaction of a monoclonal antibody and Nodal peptides by STD-NMR spectroscopy

Nodal is a growth factor expressed during early embryonic development, but reactivated in several advanced-stage cancers. Targeting of Nodal signaling, which occurs via the binding to Cripto-1 co-receptor, results in inhibition of cell aggressiveness and reduced tumor growth. The Nodal binding region to Cripto-1 was identified and targeted with a high affinity monoclonal antibody (3D1). By STD-NMR technique, we investigated the interaction of Nodal fragments with 3D1 with the aim to elucidate at atomic level the interaction surface. Data indicate with high accuracy the antibody-antigen contact atoms and confirm the information previously obtained by immune-enzymatic methods. Main residues contacted by 3D1 are P46, V47, E49 and E50, which belong to the Nodal loop involved in the interaction with the co-receptor.

A fluorescence-based array screen for transglutaminase substrates

Transglutaminases (EC 2.3.2.13) form an enzyme family that catalyzes the formation of isopeptide bonds between the γ-carboxamide group of glutamine and the ε-amine group of lysine residues of peptides and proteins. Other primary amines can be accepted in place of lysine. Because of their important physiological and pathophysiological functions, transglutaminases have been studied for 60 years. However, the substrate preferences of this enzyme class remain largely elusive. In this study, we used focused combinatorial libraries of 400 peptides to investigate the influence of the amino acids adjacent to the glutamine and lysine residues on the catalysis of isopeptide bond formation by microbial transglutaminase. Using the peptide microarray technology we found a strong positive influence of hydrophobic and basic amino acids, especially arginine, tyrosine, and leucine. Several tripeptide substrates were synthesized, and enzymatic kinetic parameters were determined both by microarray analysis and in solution.