Promotion of multipoint covalent immobilization through different regions of genetically modified penicillin G acylase from E. coli

Immobilization of Penicillin G Acylase on Vinyl Sulfone-Agarose: An Unexpected Effect of the Ionic Strength on the Performance of the Immobilization Process

Penicillin G acylase (PGA) from Escherichia coli was immobilized on vinyl sulfone (VS) agarose. The immobilization of the enzyme failed at all pH values using 50 mM of buffer, while the progressive increase of ionic strength permitted its rapid immobilization under all studied pH values. This suggests that the moderate hydrophobicity of VS groups is enough to transform the VS-agarose in a heterofunctional support, that is, a support bearing hydrophobic features (able to adsorb the proteins) and chemical reactivity (able to give covalent bonds). Once PGA was immobilized on this support, the PGA immobilization on VS-agarose was optimized with the purpose of obtaining a stable and active biocatalyst, optimizing the immobilization, incubation and blocking steps characteristics of this immobilization protocol. Optimal conditions were immobilization in 1 M of sodium sulfate at pH 7.0, incubation at pH 10.0 for 3 h in the presence of glycerol and phenyl acetic acid, and final blocking with glycine or ethanolamine. This produced biocatalysts with stabilities similar to that of the glyoxyl-PGA (the most stable biocatalyst of this enzyme described in literature), although presenting just over 55% of the initially offered enzyme activity versus the 80% that is recovered using the glyoxyl-PGA. This heterofuncionality of agarose VS beads opens new possibilities for enzyme immobilization on this support.

Putting precision and elegance in enzyme immobilisation with bio-orthogonal chemistry

The covalent immobilisation of enzymes generally involves the use of highly reactive crosslinkers, such as glutaraldehyde, to couple enzyme molecules to each other or to carriers through, for example, the free amino groups of lysine residues, on the enzyme surface. Unfortunately, such methods suffer from a lack of precision. Random formation of covalent linkages with reactive functional groups in the enzyme leads to disruption of the three dimensional structure and accompanying activity losses. This review focuses on recent advances in the use of bio-orthogonal chemistry in conjunction with rec-DNA to affect highly precise immobilisation of enzymes. In this way, cost-effective combination of production, purification and immobilisation of an enzyme is achieved, in a single unit operation with a high degree of precision. Various bio-orthogonal techniques for putting this precision and elegance into enzyme immobilisation are elaborated. These include, for example, fusing (grafting) peptide or protein tags to the target enzyme that enable its immobilisation in cell lysate or incorporating non-standard amino acids that enable the application of bio-orthogonal chemistry.

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

Enzyme immobilization has been developing since the 1960s and although many industrial biocatalytic processes use the technology to improve enzyme performance, still today we are far from full exploitation of the field. One clear reason is that many evaluate immobilization based on only a few experiments that are not always well-designed. In contrast to many other reviews on the subject, here we highlight the pitfalls of using incorrectly designed immobilization protocols and explain why in many cases sub-optimal results are obtained. We also describe solutions to overcome these challenges and come to the conclusion that recent developments in material science, bioprocess engineering and protein science continue to open new opportunities for the future. In this way, enzyme immobilization, far from being a mature discipline, remains as a subject of high interest and where intense research is still necessary to take full advantage of the possibilities.

Selective Coimmobilization of His-Tagged Enzymes on Yttrium-Stabilized Zirconia-Based Membranes for Continuous Asymmetric Bioreductions

Scalability, process control, and modularity are some of the advantages that make flow biocatalysis a key-enabling technology for green and sustainable chemistry. In this context, rigid porous solid membranes hold the promise to expand the toolbox of flow biocatalysis due to their chemical stability and inertness. Yttrium-stabilized zirconia (YSZ) fulfills these properties; however, it has been scarcely exploited as a carrier for enzymes. Here, we discovered an unprecedented interaction between YSZ materials and His-tagged enzymes that enables the fabrication of multifunctional biocatalytic membranes for bioredox cascades. X-ray photoelectron spectroscopy suggests that enzyme immobilization is driven by coordination interactions between the imidazole groups of His-tags and both Zr and Y atoms. As model enzymes, we coimmobilized in-flow a thermophilic hydroxybutyryl-CoA dehydrogenase (TtHBDH-His) and a formate dehydrogenase (His-CbFDH) for the continuous asymmetric reduction of ethyl acetoacetate with in situ redox cofactor recycling. Fluorescence confocal microscopy deciphered the spatial organization of the two coimmobilized enzymes, pointing out the importance of the coimmobilization sequence. Finally, the coimmobilized system succeeded in situ, recycling the redox cofactor, maintaining the specific productivity using only 0.05 mM NADH, and accumulating a total enzyme turnover number of 4000 in 24 h. This work presents YSZ materials as ready-to-use carriers for the site-directed enzyme in-flow immobilization and the application of the resulting heterogeneous biocatalysts for continuous biomanufacturing.

Stabilization of enzymes via immobilization: Multipoint covalent attachment and other stabilization strategies

The use of enzymes in industrial processes requires the improvement of their features in many instances. Enzyme immobilization, a requirement to facilitate the recovery and reuse of these water-soluble catalysts, is one of the tools that researchers may utilize to improve many of their properties. This review is focused on how enzyme immobilization may improve enzyme stability. Starting from the stabilization effects that an enzyme may experience by the mere fact of being inside a solid particle, we detail other possibilities to stabilize enzymes: generation of favorable enzyme environments, prevention of enzyme subunit dissociation in multimeric enzymes, generation of more stable enzyme conformations, or enzyme rigidification via multipoint covalent attachment. In this last point, we will discuss the features of an "ideal" immobilization protocol to maximize the intensity of the enzyme-support interactions. The most interesting active groups in the support (glutaraldehyde, epoxide, glyoxyl and vinyl sulfone) will be also presented, discussing their main properties and uses. Some instances in which the number of enzyme-support bonds is not directly related to a higher stabilization will be also presented. Finally, the possibility of coupling site-directed mutagenesis or chemical modification to get a more intense multipoint covalent immobilization will be discussed.

Effect of Tris Buffer in the Intensity of the Multipoint Covalent Immobilization of Enzymes in Glyoxyl-Agarose Beads

Tris is an extensively used buffer that presents a primary amine group on its structure. In the present work trypsin, chymotrypsin and penicillin G acylase (PGA) were immobilized/stabilized on glyoxyl agarose in presence of different concentrations of Tris (from 0 to 20 mM). The effects of the presence of Tris during immobilization were studied analyzing the thermal stability of the obtained immobilized biocatalysts. The results indicate a reduction of the enzyme stability when immobilized in the presence of Tris. This effect can be observed in inactivations carried out at pH 5, 7, and 9 with all the enzymes assayed. The reduction of enzyme stability increased with the Tris concentration. Another interesting result is that the stability reduction was more noticeable for immobilized PGA than in the other immobilized enzymes, the biocatalysts prepared in presence of 20 mM Tris lost totally the activity at pH 7 just after 1 h of inactivation, while the reference at this time still kept around 61 % of the residual activity. These differences are most likely due to the homogeneous distribution of the Lys groups in PGA compared to trypsin and chymotrypsin (where almost 50% of Lys group are in a small percentage of the protein surface). The results suggest that Tris could be affecting the multipoint covalent immobilization in two different ways, on one hand, reducing the number of available glyoxyl groups of the support during immobilization, and on the other hand, generating some steric hindrances that difficult the formation of covalent bonds.

Effect of amine length in the interference of the multipoint covalent immobilization of enzymes on glyoxyl agarose beads

Trypsin, chymotrypsin, penicillin G acylase and ficin extract have been stabilized by immobilization on glyoxyl agarose, adding different aliphatic compounds bearing a primary amine group during the immobilization: ethyl amine, butyl amine, hexyl amine (at concentrations ranging from 0 to 20 mM) and octyl amine (from 0 to 10 mM) to analyze their effects on the immobilized enzyme stability. As expected, the presence of amines reduced the intensity of the enzyme-support multipoint covalent attachment, and therefore the enzyme stability. However, it is clear that this effect is higher using octyl amine for all enzymes (in some cases the enzyme immobilized in the presence of 10 mM octyl amine was almost inactivated while the reference kept over 50 % of the initial activity). This way, it seems that the most important effect of the presence of aminated compounds came from the generation of steric hindrances to the enzyme/support multi-reaction promoted by the ammines that are interacting with the aldehyde groups. In some instances, just 1 mM of aminated compounds is enough to greatly decrease enzyme stability. The results suggested that, if the composition of the enzyme extract is unknown, to eliminate small aminated compounds may be necessary to maximize the enzyme-support reaction.

The Science of Enzyme Immobilization

Protocols for simple immobilization of unstable enzymes are plenty, but the vast majority of them, unfortunately, have not reached their massive implementation for the preparation of improved heterogeneous biocatalyst. In this context, the science of enzyme immobilization demands new protocols capable of fabricating heterogeneous biocatalysts with better properties than the soluble enzymes. The preparation of very stable immobilized biocatalysts enables the following: (1) higher operational times of enzyme, increasing their total turnover numbers; (2) the use of enzymes under non-conventional media (temperatures, solvents, etc.) in order to increase the concentrations of substrates for intensification of processes or in order to shift reaction equilibria; (3) the design of solvent-free reaction systems; and (4) the prevention of microbial contaminations. These benefits gained with the immobilization are critical to scale up chemical processes like the synthesis of biodiesel, synthesis of food additives or soil decontamination, where the cost of the catalysts has an enormous impact on their economic feasibility. The science of enzyme immobilization requires a multidisciplinary focus that involves several areas of knowledge such as, material science, surface chemistry, protein chemistry, biophysics, molecular biology, biocatalysis, and chemical engineering. In this chapter, we will discuss the most relevant aspects to do "the science of enzyme immobilization." We will emphasize the immobilization techniques that promote multivalent attachments between the surface of the enzymes and the porous carriers. Finally, we will discuss the effect that the structural rigidification promotes at different protein regions on the functional properties of the immobilized enzymes.

Preparation of immobilized/stabilized biocatalysts of β-glucosidases from different sources: Importance of the support active groups and the immobilization protocol

β-Glucosidases from two different commercial preparations, Pectinex Ultra SP-L and Celluclast® 1.5L, were immobilized on divinylsulfone (DVS) supports at pH 5.0, 7.0, 9.0, and 10. In addition, the biocatalysts were also immobilized in agarose beads activated by glyoxyl, and epoxide as reagent groups. The best immobilization results were observed using higher pH values on DVS-agarose, and for Celluclast® 1.5L, good results were also obtained using the glyoxil-agarose immobilization. The biocatalyst obtained using Pectinex Ultra SP-L showed the highest thermal stability, at 65°C, and an operational stability of 67% of activity after 10 reuses cycles when immobilized on DVS-agarose immobilized at pH 10 and blocked with ethylenediamine. The β-glucosidase from Celluclast® 1.5L produced best results when immobilized on DVS-agarose immobilized at pH 9 and blocked with glycine, reaching 7.76-fold higher thermal stability compared to its free form and maintaining 76% of its activity after 10 successive cycles. The new biocatalysts obtained by these protocols showed reduction of glucose inhibition of enzymes, demonstrating the influence of immobilization protocols, pH, and blocking agent.

Stabilization of Enzymes by Multipoint Covalent Attachment on Aldehyde-Supports: 2-Picoline Borane as an Alternative Reducing Agent

Enzyme immobilization by multipoint covalent attachment on supports activated with aliphatic aldehyde groups (e.g., glyoxyl agarose) has proven to be an excellent immobilization technique for enzyme stabilization. Borohydride reduction of immobilized enzymes is necessary to convert enzyme–support linkages into stable secondary amino groups and to convert the remaining aldehyde groups on the support into hydroxy groups. However, the use of borohydride can adversely affect the structure–activity of some immobilized enzymes. For this reason, 2-picoline borane is proposed here as an alternative milder reducing agent, especially, for those enzymes sensitive to borohydride reduction. The immobilization-stabilization parameters of five enzymes from different sources and nature (from monomeric to multimeric enzymes) were compared with those obtained by conventional methodology. The most interesting results were obtained for bacterial (R)-mandelate dehydrogenase (ManDH). Immobilized ManDH reduced with borohydride almost completely lost its catalytic activity (1.5% of expressed activity). In contrast, using 2-picoline borane and blocking the remaining aldehyde groups on the support with glycine allowed for a conjugate with a significant activity of 19.5%. This improved biocatalyst was 357-fold more stable than the soluble enzyme at 50 °C and pH 7. The results show that this alternative methodology can lead to more stable and active biocatalysts.

Agarose and Its Derivatives as Supports for Enzyme Immobilization

Agarose is a polysaccharide obtained from some seaweeds, with a quite particular structure that allows spontaneous gelation. Agarose-based beads are highly porous, mechanically resistant, chemically and physically inert, and sharply hydrophilic. These features-that could be further improved by means of covalent cross-linking-render them particularly suitable for enzyme immobilization with a wide range of derivatization methods taking advantage of chemical modification of a fraction of the polymer hydroxyls. The main properties of the polymer are described here, followed by a review of cross-linking and derivatization methods. Some recent, innovative procedures to optimize the catalytic activity and operational stability of the obtained preparations are also described, together with multi-enzyme immobilized systems and the main guidelines to exploit their performances.

Inactivation of immobilized trypsin under dissimilar conditions produces trypsin molecules with different structures

Bovine trypsin immobilized on glyoxyl agarose and submitted to different inactivation conditions produce different conformations.

Versatility of divinylsulfone supports permits the tuning of CALB properties during its immobilization

Properties of CALB has been modulated by immobilization on divinylsulfone (DVS) activated agarose beads under different conditions (pH 5–10).

Characterization of supports activated with divinyl sulfone as a tool to immobilize and stabilize enzymes via multipoint covalent attachment. Application to chymotrypsin

DVS supports are very suitable to stabilize enzymes via multipoint covalent attachment.

Reversible covalent immobilization of enzymes via disulfide bonds

This enzyme immobilization approach involves the formation of disulfide (-S-S-) bonds with the support. Thus, enzymes bearing exposed nonessential thiol (SH) groups can be immobilized onto thiol-reactive supports provided with reactive disulfides or disulfide oxides under mild conditions. The great potential advantage of this approach is the reversibility of the bonds formed between the activated solid phase and the thiol-enzyme, because the bound protein can be released with an excess of a low-molecular-weight thiol (e.g., dithiothreitol [DTT]). This is of particular interest when the enzyme degrades much faster than the adsorbent, which can be reloaded afterwards. The possibility of reusing the polymeric support after inactivation of the enzyme may be of interest for the practical use of immobilized enzymes in large-scale processes in industry, where their use has often been hampered by the high cost of the support material. Disulfide oxides (thiolsulfinate or thiolsulfonate groups) can be introduced onto a wide variety of support materials with different degrees of porosity and with different mechanical resistances. Procedures are given for the preparation of thiol-activated solid phases and the covalent attachment of thiol-enzymes to the support material via disulfide bonds. The possibility of reusing the polymeric support is also shown.

New biotechnological perspectives of a NADH oxidase variant from Thermus thermophilus HB27 as NAD+-recycling enzyme

Background

The number of biotransformations that use nicotinamide recycling systems is exponentially growing. For this reason one of the current challenges in biocatalysis is to develop and optimize more simple and efficient cofactor recycling systems. One promising approach to regenerate NAD⁺ pools is the use of NADH-oxidases that reduce oxygen to hydrogen peroxide while oxidizing NADH to NAD⁺. This class of enzymes may be applied to asymmetric reduction of prochiral substrates in order to obtain enantiopure compounds.

Results

The NADH-oxidase (NOX) presented here is a flavoenzyme which needs exogenous FAD or FMN to reach its maximum velocity. Interestingly, this enzyme is 6-fold hyperactivated by incubation at high temperatures (80°C) under limiting concentrations of flavin cofactor, a change that remains stable even at low temperatures (37°C). The hyperactivated form presented a high specific activity (37.5 U/mg) at low temperatures despite isolation from a thermophile source. Immobilization of NOX onto agarose activated with glyoxyl groups yielded the most stable enzyme preparation (6-fold more stable than the hyperactivated soluble enzyme). The immobilized derivative was able to be reactivated under physiological conditions after inactivation by high solvent concentrations. The inactivation/reactivation cycle could be repeated at least three times, recovering full NOX activity in all cases after the reactivation step. This immobilized catalyst is presented as a recycling partner for a thermophile alcohol dehydrogenase in order to perform the kinetic resolution secondary alcohols.

Conclusion

We have designed, developed and characterized a heterogeneous and robust biocatalyst which has been used as recycling partner in the kinetic resolution of rac-1-phenylethanol. The high stability along with its capability to be reactivated makes this biocatalyst highly re-useable for cofactor recycling in redox biotransformations.

Enhancing the functional properties of thermophilic enzymes by chemical modification and immobilization

The immobilization of proteins (mostly typically enzymes) onto solid supports is mature technology and has been used successfully to enhance biocatalytic processes in a wide range of industrial applications. However, continued developments in immobilization technology have led to more sophisticated and specialized applications of the process. A combination of targeted chemistries, for both the support and the protein, sometimes in combination with additional chemical and/or genetic engineering, has led to the development of methods for the modification of protein functional properties, for enhancing protein stability and for the recovery of specific proteins from complex mixtures. In particular, the development of effective methods for immobilizing large multi-subunit proteins with multiple covalent linkages (multi-point immobilization) has been effective in stabilizing proteins where subunit dissociation is the initial step in enzyme inactivation. In some instances, multiple benefits are achievable in a single process. Here we comprehensively review the literature pertaining to immobilization and chemical modification of different enzyme classes from thermophiles, with emphasis on the chemistries involved and their implications for modification of the enzyme functional properties. We also highlight the potential for synergies in the combined use of immobilization and other chemical modifications.

Taking advantage of unspecific interactions to produce highly active magnetic nanoparticle-antibody conjugates

Several strategies for linking antibodies (Abs) through their Fc region in an oriented manner have been proposed at the present time. By using these strategies, the Fab region of the Ab is available for antigen molecular recognition, leading to a more efficient interaction. Most of these strategies are complex processes optimized mainly for the functionalization of surfaces or microbeads. These methodologies imply though the Ab modification through several steps of purification or the use of expensive immobilized proteins. Besides, the functionalization of magnetic nanoparticles (MNPs) turned out to be much more complex than expected due to the lack of stability of most MNPs at high ionic strength and non-neutral pH values. Therefore, there is still missing an efficient, easy and universal methodology for the immobilization of nonmodified Abs onto MNPs without involving their Fab regions during the immobilization process. Herein, we propose the functionalization of MNPs via a two-steps strategy that takes advantage of the ionic reversible interactions between the Ab and the MNP. These interactions make possible the orientation of the Ab on the MNP surface before being attached in an irreversible way via covalent bonds. Three Abs (Immunoglobulin G class) with very different isoelectric points (against peroxidase, carcinoembryonic antigen, and human chorionic gonadotropin hormone) were used to prove the general applicability of the strategy here proposed and its utility for the development of more bioactive NPs.

Control of protein immobilization: coupling immobilization and site-directed mutagenesis to improve biocatalyst or biosensor performance

Mutagenesis and immobilization are usually considered to be unrelated techniques with potential applications to improve protein properties. However, there are several reports showing that the use of site-directed mutagenesis to improve enzyme properties directly, but also how enzymes are immobilized on a support, can be a powerful tool to improve the properties of immobilized biomolecules for use as biosensors or biocatalysts. Standard immobilizations are not fully random processes, but the protein orientation may be difficult to alter. Initially, most efforts using this idea were addressed towards controlling the orientation of the enzyme on the immobilization support, in many cases to facilitate electron transfer from the support to the enzyme in redox biosensors. Usually, Cys residues are used to directly immobilize the protein on a support that contains disulfide groups or that is made from gold. There are also some examples using His in the target areas of the protein and using supports modified with immobilized metal chelates and other tags (e.g., using immobilized antibodies). Furthermore, site-directed mutagenesis to control immobilization is useful for improving the activity, the stability and even the selectivity of the immobilized protein, for example, via site-directed rigidification of selected areas of the protein. Initially, only Cys and disulfide supports were employed, but other supports with higher potential to give multipoint covalent attachment are being employed (e.g., glyoxyl or epoxy-disulfide supports). The advances in support design and the deeper knowledge of the mechanisms of enzyme-support interactions have permitted exploration of the possibilities of the coupled use of site-directed mutagenesis and immobilization in a new way. This paper intends to review some of the advances and possibilities that these coupled strategies permit.