Immobilization of alkaline phosphatase on magnetic particles by site-specific and covalent cross-linking catalyzed by microbial transglutaminase

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.

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.

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.

Magnetic beads assay based on Zip nucleic acid for electrochemical detection of Factor V Leiden mutation

Single nucleotide polymorphisms (SNPs) are the most common type of genetic variation among people. Development of reliable methods for the detection of SNP is crucial in aspects of molecular diagnosis and personalized medicine. In our study, a genomagnetic assay in combination with zip nucleic acid (ZNA) for electrochemical detection of SNP related to Factor V Leiden mutation. For the first time in the literature, a new generation nucleic acid; ZNA was applied herein for electrochemical monitoring of nucleic acid hybridization. Streptavidin coated magnetic beads (MBs) were used for preparation of samples containing ZNA-DNA hybrid and accordingly, the guanine signal was measured as a response of hybridization related to Factor V Leiden mutation by carbon nanofibers (CNF) modified screen printed electrodes (SPE) and multi-channel screen printed array of electrodes (CNF-MULTI SPEx8). The detection limit (DL) was found to be 3.79 μg/mL (376 nM) and, 11.63 μg/mL (1.624 μM), respectively by CNF-SPE and CNF-MULTI SPEx8. The selectivity of ZNA probe to mutation-free DNA sequences was also investigated in contrast to DNA probe. The applicability of ZNA based magnetic beads assay to sequence selective hybridization related to Factor V Leiden was also tested in synthetic PCR samples.

Biofabricating Functional Soft Matter Using Protein Engineering to Enable Enzymatic Assembly

Biology often provides the inspiration for functional soft matter, but biology can do more: it can provide the raw materials and mechanisms for hierarchical assembly. Biology uses polymers to perform various functions, and biologically derived polymers can serve as sustainable, self-assembling, and high-performance materials platforms for life-science applications. Biology employs enzymes for site-specific reactions that are used to both disassemble and assemble biopolymers both to and from component parts. By exploiting protein engineering methodologies, proteins can be modified to make them more susceptible to biology's native enzymatic activities. They can be engineered with fusion tags that provide (short sequences of amino acids at the C- and/or N- termini) that provide the accessible residues for the assembling enzymes to recognize and react with. This "biobased" fabrication not only allows biology's nanoscale components (i.e., proteins) to be engineered, but also provides the means to organize these components into the hierarchical structures that are prevalent in life.

Catechol-chitosan redox capacitor for added amplification in electrochemical immunoanalysis

Antibodies are common recognition elements for molecular detection but often the signals generated by their stoichiometric binding must be amplified to enhance sensitivity. Here, we report that an electrode coated with a catechol-chitosan redox capacitor can amplify the electrochemical signal generated from an alkaline phosphatase (AP) linked immunoassay. Specifically, the AP product p-aminophenol (PAP) undergoes redox-cycling in the redox capacitor to generate amplified oxidation currents. We estimate an 8-fold amplification associated with this redox-cycling in the capacitor (compared to detection by a bare electrode). Importantly, this capacitor-based amplification is generic and can be coupled to existing amplification approaches based on enzyme-linked catalysis or magnetic nanoparticle-based collection/concentration. Thus, the capacitor should enhance sensitivities in conventional immunoassays and also provide chemical to electrical signal transduction for emerging applications in molecular communication.

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.

Possible association between celiac disease and bacterial transglutaminase in food processing: a hypothesis

The incidence of celiac disease is increasing worldwide, and human tissue transglutaminase has long been considered the autoantigen of celiac disease. Concomitantly, the food industry has introduced ingredients such as microbial transglutaminase, which acts as a food glue, thereby revolutionizing food qualities. Several observations have led to the hypothesis that microbial transglutaminase is a new environmental enhancer of celiac disease. First, microbial transglutaminase deamidates/transamidates glutens such as the endogenous human tissue transglutaminase. It is capable of crosslinking proteins and other macromolecules, thereby changing their antigenicity and resulting in an increased antigenic load presented to the immune system. Second, it increases the stability of protein against proteinases, thus diminishing foreign protein elimination. Infections and the crosslinked nutritional constituent gluten and microbial transglutaminase increase the permeability of the intestine, where microbial transglutaminases are necessary for bacterial survival. The resulting intestinal leakage allows more immunogenic foreign molecules to induce celiac disease. The increased use of microbial transglutaminase in food processing may promote celiac pathogenesis ex vivo, where deamidation/transamidation starts, possibly explaining the surge in incidence of celiac disease. If future research substantiates this hypothesis, the findings will affect food product labeling, food additive policies of the food industry, and consumer health education.

Fabrication of uniformly cell-laden porous scaffolds using a gas-in-liquid templating technique

Design of porous scaffolds in tissue engineering field was challenging. Uniform immobilization of cells in the scaffolds with high porosity was essential for homogeneous tissue formation. The present study was aimed at fabricating uniformly cell-laden porous scaffolds with porosity >74% using the gas-in-liquid foam templating technique. To this end, we used gelatin, microbial transglutaminase and argon gas as a scaffold material, cross-linker of the protein and porogen of scaffold, respectively. We confirmed that a porosity of >74% could be achieved by increasing the gas volume delivered to a gelatin solution. Pore size in the scaffold could be controlled by stirring speed, stirring time and the pore size of the filter through which the gas passed. The foaming technique enabled us to uniformly immobilize a human hepatoblastoma cell line in scaffold. Engraftment efficiency of the cell line entrapped within the scaffold in nude mice was higher than that of cells in free-form. These results showed that the uniformly cell-laden porous scaffolds were promising for tissue engineering.

Microbial transglutaminase and c-myc-tag: a strong couple for the functionalization of antibody-like protein scaffolds from discovery platforms

Antibody-like proteins selected from discovery platforms are preferentially functionalized by site-specific modification as this approach preserves the binding abilities and allows a side-by-side comparison of multiple conjugates. Here we present an enzymatic bioconjugation platform that targets the c-myc-tag peptide sequence (EQKLISEEDL) as a handle for the site-specific modification of antibody-like proteins. Microbial transglutaminase (MTGase) was exploited to form a stable isopeptide bond between the glutamine on the c-myc-tag and various primary-amine-functionalized substrates. We attached eight different functionalities to a c-myc-tagged antibody fragment and used these bioconjugates for downstream applications such as protein multimerization, immobilization on surfaces, fluorescence microscopy, fluorescence-activated cell sorting, and in vivo nuclear imaging. The results demonstrate the versatility of our conjugation strategy for transforming a c-myc-tagged protein into any desired probe.

Magnetic nanoparticles as new diagnostic tools in medicine

Magnetic iron oxide nanoparticles have raised much interest during the recent years due to their novel properties (superparamagnetism, high saturation field, blocking temperature, etc.) and potential applications in organic synthesis, biotechnology and finally in medicine. The medicinal applications include: controlled drug delivery systems (DDS), magnetic resonance imaging (MRI), magnetic fluid hyperthermia (MFH), macromolecules and pathogens separation, cancer therapy and so on. In this paper we would like to present the newest literature reports concerning usage of MNPs in medicinal diagnostics such as: - magnetic separations of DNA (immobilization, isolation, diagnosis of genetic disorders and detection of exogenous substances in the organisms) - magnetic immobilization of proteins (applications in biotechnology, medicine, and catalysis) - magnetic separations of pathogens (i.e. isolation of bacteria, detection of various pathogens) - magnetic resonance imaging (imaging contrast agents, lymphangiography).

Iron oxide filled magnetic carbon nanotube-enzyme conjugates for recycling of amyloglucosidase: toward useful applications in biofuel production process

Biofuels are fast advancing as a new research area to provide alternative sources of sustainable and clean energy. Recent advances in nanotechnology have sought to improve the efficiency of biofuel production, enhancing energy security. In this study, we have incorporated iron oxide nanoparticles into single-walled carbon nanotubes (SWCNTs) to produce magnetic single-walled carbon nanotubes (mSWCNTs). Our objective is to bridge both nanotechnology and biofuel production by immobilizing the enzyme, Amyloglucosidase (AMG), onto mSWCNTs using physical adsorption and covalent immobilization, with the aim of recycling the immobilized enzyme, toward useful applications in biofuel production processes. We have demonstrated that the enzyme retains a certain percentage of its catalytic efficiency (up to 40%) in starch prototype biomass hydrolysis when used repeatedly (up to ten cycles) after immobilization on mSWCNTs, since the nanotubes can be easily separated from the reaction mixture using a simple magnet. The enzyme loading, activity, and structural changes after immobilization onto mSWCNTs were also studied. In addition, we have demonstrated that the immobilized enzyme retains its activity when stored at 4 °C for at least one month. These results, combined with the unique intrinsic properties of the nanotubes, pave the way for greater efficiency in carbon nanotube-enzyme bioreactors and reduced capital costs in industrial enzyme systems.

Site-specific protein labeling with amine-containing molecules using Lactobacillus plantarum sortase

Modification of proteins with small molecules is a widely used and powerful tool in biological research. Enzymatic approaches are particularly promising because substrate specificity allows for site-specific modification. Sortase A, a transpeptidase from Staphylococcus aureus, cleaves between the T and G residues in the sequence LPXTG, and subsequently links the carboxyl group of the T residue to an amino group of N-terminal glycine oligomers by a native peptide bond. Although Gram-positive bacteria have several kinds of sortases, there are few reports concerning their expression and substrate specificity. Here, we demonstrate site-specific protein modification with primary amine-containing molecules catalyzed by Lactobacillus plantarum sortase. Enhanced green fluorescent protein (EGFP) was employed as a model protein, and an amine-containing biotin molecule was site-specifically conjugated with LPQTSEQ-tagged EGFP. We developed a novel Lactobacillus plantarum sortase that has different substrate specificity compared to Staphylococcus aureus sortase. Amine-directed protein modification was achieved using the Lactobacillus plantarum sortase ''LPQTSEQ'' sequence original recognition tag. Our results demonstrate a promising method for expanding the capabilities of site-specific protein-small molecule modification.