Kinetic and thermodynamic characterization of the functional properties of a hybrid versatile peroxidase using isothermal titration calorimetry: Insight into manganese peroxidase activation and lignin peroxidase inhibition

Peroxidases-based enticing biotechnological platforms for biodegradation and biotransformation of emerging contaminants

Rampant industrial boom, urbanization, and exponential population growth resulted in widespread environmental pollution, with water being one of the leading affected resources. All kinds of pollutants, including phenols, industrial dyes, antibiotics, pharmaceutically active residues, and persistent/volatile organic compounds, have a paramount effect, either directly or indirectly, on human health and aquatic entities. Strategies for affordable and efficient decontamination of these emerging pollutants have become the prime focus of academic researchers, industry, and government to constitute a sustainable human society. Classical treatment techniques for environmental contaminants are associated with several limitations, such as inefficiency, complex pretreatments, overall high process cost, high sludge generation, and highly toxic side-products formation. Enzymatic remediation is considered a green and ecologically friendlier method that holds considerable potential to mitigate any kinds of contaminating agents. Exploiting the potential of various peroxidases for pollution abatement is an emerging research area and has considerable advantages, such as efficiency and ease of handling, over other methods. This work is designed to provide recent progress in deploying peroxidases as green and versatile biocatalytic tools for the degradation and transformation of a spectrum of potentially hazardous environmental pollutants to broaden their scope for biotechnological and environmental purposes. More studies are required to explicate the degradation mechanisms, assess the toxicology levels of bio-transformed metabolites, and standardize the treatment strategies for economic viability.

The use of isothermal titration calorimetry for the assay of enzyme activity: Application in higher education practical classes

Determination of enzyme activity is crucial for discovery, research, and development in life sciences. The activity of enzymes is routinely determined using spectrophotometric assays that measure rates of substrate consumption or product formation. Though colorimetric-based detection systems are simple, rapid, and economical to perform, the majority of enzymes are unsuitable for this technique as their substrates/products do not absorb in the UV or visible range. This limitation can be addressed by the use of coupled-enzyme assays or artificial chromogenic substrates; however these approaches have their own drawbacks. Here, we describe a method based on the use of an isothermal titration calorimeter (ITC) to measure the heat produced or absorbed during any enzyme-catalyzed reaction. The concept of calorimetric enzyme assays was demonstrated for the determination of enzyme hexokinase activity, which cannot be monitored colorimetrically without first coupling it to another enzymatic reaction. The assay is suitable for incorporation into undergraduate laboratory classes, providing students with an appreciation for; the versatility and ease of use of ITC assays; ITC as a flexible generic method for exploring the functional characteristics of uncharacterized enzymes; an activity detection parameter suitable for enzymes that either have no straightforward colorimetric methods available or require the use of nonartificial chromogenic substrates.

Evaluating Enzymatic Productivity—The Missing Link to Enzyme Utility

Kinetic productivity analysis is critical to the characterization of enzyme catalytic performance and capacity. However, productivity analysis has been largely overlooked in the published literature. Less than 0.01% of studies which report on enzyme characterization present productivity analysis, despite the fact that this is the only measurement method that provides a reliable indicator of potential commercial utility. Here, we argue that reporting productivity data involving native, modified, and immobilized enzymes under different reaction conditions will be of immense value in optimizing enzymatic processes, with a view to accelerating biotechnological applications. With the use of examples from wide-ranging studies, we demonstrate that productivity is a measure of critical importance to the translational and commercial use of enzymes and processes that employ them. We conclude the review by suggesting steps to maximize the productivity of enzyme catalyzed reactions.

Current understanding and insights towards protein stabilization and activation in deep eutectic solvents as sustainable solvent media

Deep eutectic solvents (DESs) have emerged as a new class of green, designer and biocompatible solvents, an alternative to conventional organic solvents and ionic liquids (ILs) which are comparatively toxic and non-biodegradable. DESs are eutectic mixtures that are formed when a hydrogen bond acceptor (HBA) is mixed with a hydrogen bond donor (HBD) at particular molar ratios by mechanical grinding or under mild heating conditions. Very recently, these solvents have been the center of attention for researchers in biotechnology, biomedicine and various scientific applications. These environmentally benign solvents have a close analogy with ILs; however, they offer certain unique merits over traditional ILs. DESs display remarkable properties such as easy preparation, tunable composition, biodegradability, recyclability, inherently low toxicity, sustainability and biocompatibility; these special features validate DESs as new potential solvents/co-solvents for biomolecules. Mechanistically, the biocompatibility and protein friendly nature of DESs depend on various factors, which include the composition of the DES, viscosity and hydration level. Therefore, it becomes an essential task to bring together all the studies related to protein behaviour in DESs to unlock their biomolecular proficiency. This review specifically highlights recent insights into the biomacromolecular functionality in DESs, including outlines of the solubilization and stabilization of proteins, long term protein packaging, different extraction methods and enzyme activation in the presence of DESs. A literature survey reveals that DESs act as green media in which the protein structure and activity are retained. In some cases, proteins refolded and enzymatic activity was enhanced several fold in the presence of DESs. Furthermore, we have reviewed the possible mechanistic behaviour behind protein stabilization, refolding and activation in DESs. Overall, the main objective of this review is to explicate the advantages of the introduction of DESs for biomolecules and to demonstrate the versatility of these eco-friendly solvents for future bio-based applications.

Peroxidase enzymes as green catalysts for bioremediation and biotechnological applications: A review

The fast-growing consumer demand drives industrial process intensification, which subsequently creates a significant amount of waste. These products are discharged into the environment and can affect the quality of air, degrade water streams, and alter soil characteristics. Waste materials may contain polluting agents that are especially harmful to human health and the ecosystem, such as the synthetic dyes, phenolic agents, polycyclic aromatic hydrocarbons, volatile organic compounds, polychlorinated biphenyls, pesticides and drug substances. Peroxidases are a class oxidoreductases capable of performing a wide variety of oxidation reactions, ranging from reactions driven by radical mechanisms, to oxygen insertion into CH bonds, and two-electron substrate oxidation. This versatility in the mode of action presents peroxidases as an interesting alternative in cleaning the environment. Herein, an effort has been made to describe mechanisms governing biochemical process of peroxidase enzymes while referring to H₂O₂/substrate stoichiometry and metabolite products. Plant peroxidases including horseradish peroxidase (HRP), soybean peroxidase (SBP), turnip and bitter gourd peroxidases have revealed notable biocatalytic potentialities in the degradation of toxic products. On the other hand, an introduction on the role played by ligninolytic enzymes such as manganese peroxidase (MnP) and lignin peroxidase (LiP) in the valorization of lignocellulosic materials is addressed. Moreover, sensitivity and selectivity of peroxidase-based biosensors found use in the quantitation of constituents and the development of diagnostic kits. The general merits of peroxidases and some key prospective applications have been outlined as concluding remarks.

Functional Characterization of Melanin Decolorizing Extracellular Peroxidase of Bjerkandera adusta

Melanin pigmentation in the human skin results from complicated cellular mechanisms that remain to be entirely understood. Uneven melanin pigmentation has been counteracted by inhibiting synthesis or transfer of melanin in the skin. Recently, an enzymatic approach has been proposed, wherein the melanin in the skin is decolorized using lignin peroxidase. However, not many enzymes are available for decolorizing melanin; the most studied one is lignin peroxidase derived from a lignin degrading fungus, Phanerochaete chrysosporium. Our current study reveals that versatile peroxidase from Bjerkandera adusta can decolorize synthetic melanin. Melanin decolorization was found to be dependent on veratryl alcohol and hydrogen peroxide, but not on Mn²⁺. The degree of decolorization reached over 40% in 10 min at 37 °C and a pH of 4.5. Optimized storage conditions were slightly different from those for the reaction; crude enzyme preparation was the most stable at 25 °C at pH 5.5. Since the enzyme rapidly lost its activity at 50 °C, stabilizers were screened. As a result, glycerol, a major component in several cosmetic formulations, was found to be a promising excipient. Our results suggest that B. adusta versatile peroxidase can be considered for future cosmetic applications aimed at melanin decolorization.

Considerations about the Continuous Assay Methods, Spectrophotometric and Spectrofluorometric, of the Monophenolase Activity of Tyrosinase

With the purpose to obtain the more useful tyrosinase assay for the monophenolase activity of tyrosinase between the spectrofluorometric and spectrophotometric continuous assays, simulated assays were made by means of numerical integration of the equations that characterize the mechanism of monophenolase activity. These assays showed that the rate of disappearance of monophenol (VssM,M) is equal to the rate of accumulation of dopachrome (VssM,DC) or to the rate of accumulation of its oxidized adduct, originated by the nucleophilic attack on o-quinone by a nucleophile such as 3-methyl-2-benzothiazolinone (MBTH), (VssM, A−ox), despite the existence of coupled reactions. It is shown that the spectrophotometric methods that use MBTH are more useful, as they do not have the restrictions of the L-tyrosine disappearance measurement method, of working at pH = 8 and not having a linear response from 100 μM of L-tyrosine. It is possible to obtain low LOD^M (limit of detection of the monophenolase activity) values with spectrophotometric methods. The spectrofluorimetric methods had a lower LOD^M than spectrophotometric methods. In the case of 4-hydroxyphenil-propionic acid, the LOD^M obtained by us was 0.25 U/mL. Considering the relative sensitivities of 4-hydroxyanisole, compared with 4-hydroxyphenil-propionic acid, LOD^M values like those obtained by fluorescent methods would be expected.

Enzyme Kinetics by Isothermal Titration Calorimetry: Allostery, Inhibition, and Dynamics

Isothermal titration calorimetry (ITC) involves accurately measuring the heat that is released or absorbed in real time when one solution is titrated into another. This technique is usually used to measure the thermodynamics of binding reactions. However, there is mounting interest in using it to measure reaction kinetics, particularly enzymatic catalysis. This application of ITC has been steadily growing for the past two decades, and the method is proving to be sensitive, generally applicable, and capable of providing information on enzyme activity that is difficult to obtain using traditional biochemical assays. This review aims to give a broad overview of the use of ITC to measure enzyme kinetics. It describes several different classes of ITC experiment, their strengths and weaknesses, and recent methodological advancements. A summary of applications in the literature is given and several examples where ITC has been used to investigate challenging aspects of enzyme behavior are presented in more detail. These include examples of allostery, where small-molecule binding outside the active site modulates activity. We describe the use of ITC to measure the strength, mode (i.e., competitive, uncompetitive, or mixed), and association and dissociation kinetics of enzyme inhibitors. Further, we provide examples of ITC applied to complex, heterogeneous mixtures, such as insoluble substrates and live cells. These studies exemplify the wide range of problems where ITC can provide answers, and illustrate the versatility of the technique and potential for future development and applications.

Enhanced Delignification of Lignocellulosic Biomass by Recombinant Fungus Overexpressing Laccases and Peroxidases

Ligninolytic enzyme production and lignin degradation are typically the rate-limiting steps in the biofuel industry. To improve the efficiency of simultaneous bio-delignification and enzyme production, <i>Phanerochaete chrysosporium</i> was transformed by shock wave-induced acoustic cavitation to co-overexpress 3 peroxidases and 1 laccase and test it on the degradation of sugarcane bagasse and wheat bran. Lignin depolymerization was enhanced by up to 25% in the presence of recombinant fungi in comparison with the wild-type strain. Sugar release on lignocellulose was 2- to 6-fold higher by recombinant fungi as compared with the control. Wheat bran ostensibly stimulated the production of ligninolytic enzymes. The highest peroxidase activity from the recombinant strains was 2.6-fold higher, whereas the increase in laccase activity was 4-fold higher in comparison to the control. The improvement of lignin degradation was directly proportional to the highest peroxidase and laccase activity. Because various phenolic compounds released during lignocellulose degradation have proven to be toxic to cells and to inhibit enzyme activity, a significant reduction (over 40%) of the total phenolic content in the samples treated with recombinant strains was observed. To our knowledge, this is the first report that engineering <i>P. chrysosporium</i> enhances<i></i> biodegradation of lignocellulosic biomass.

Limits of Versatility of Versatile Peroxidase

Although Mn(2+) is the most abundant substrate of versatile peroxidases (VPs), repression of Pleurotus ostreatus vp1 expression occurred in Mn(2+)-sufficient medium. This seems to be a biological contradiction. The aim of this study was to explore the mechanism of direct oxidation by VP1 under Mn(2+)-deficient conditions, as it was found to be the predominant enzyme during fungal growth in the presence of synthetic and natural substrates. The native VP1 was purified and characterized using three substrates, Mn(2+), Orange II (OII), and Reactive Black 5 (RB5), each oxidized by a different active site in the enzyme. While the pH optimum for Mn(2+) oxidation is 5, the optimum pH for direct oxidation of both dyes was found to be 3. Indeed, effective in vivo decolorization occurred in media without addition of Mn(2+) only under acidic conditions. We have determined that Mn(2+) inhibits in vitro the direct oxidation of both OII and RB5 while RB5 stabilizes both Mn(2+) and OII oxidation. Furthermore, OII was found to inhibit the oxidation of both Mn(2+) and RB5. In addition, we could demonstrate that VP1 can cleave OII in two different modes. Under Mn(2+)-mediated oxidation conditions, VP1 was able to cleave the azo bond only in asymmetric mode, while under the optimum conditions for direct oxidation (absence of Mn(2+) at pH 3) both symmetric and asymmetric cleavages occurred. We concluded that the oxidation mechanism of aromatic compounds by VP1 is controlled by Mn(2+) and pH levels both in the growth medium and in the reaction mixture.

IMPORTANCE

VP1 is a member of the ligninolytic heme peroxidase gene family of the white rot fungus Pleurotus ostreatus and plays a fundamental role in biodegradation. This enzyme exhibits a versatile nature, as it can oxidize different substrates under altered environmental conditions. VPs are highly interesting enzymes due to the fact that they contain unique active sites that are responsible for direct oxidation of various aromatic compounds, including lignin, in addition to the well-known Mn(2+) binding active site. This study demonstrates the limits of versatility of P. ostreatus VP1, which harbors multiple active sites, exhibiting a broad range of enzymatic activities, but they perform differently under distinct conditions. The versatility of P. ostreatus and its enzymes is an advantageous factor in the fungal ability to adapt to changing environments. This trait expands the possibilities for the potential utilization of P. ostreatus and other white rot fungi.

Improvement of the thermostability and catalytic efficiency of a highly active β-glucanase from Talaromyces leycettanus JCM12802 by optimizing residual charge-charge interactions

BACKGROUND

β-Glucanase is one of the most extensively used biocatalysts in biofuel, food and animal feed industries. However, the poor thermostability and low catalytic efficiency of most reported β-glucanases limit their applications. Currently, two strategies are used to overcome these bottlenecks, i.e., mining for novel enzymes from extremophiles and engineering existing enzymes.

RESULTS

A novel endo-β-1,3-1,4-glucanase of GH16 (Tlglu16A) from the thermophilic fungus Talaromyces leycettanus JCM12802 was produced in Pichia pastoris and characterized. For potential industrial applications, recombinant TlGlu16A exhibits favorable enzymatic properties over most reported glucanases, i.e., remarkable stability over a wide pH range from 1.0 to 10.0 and superior activity on glucan substrates (up to 15,197 U/mg). The only weakness of TlGlu16A is the thermolability at 65 °C and higher. To improve the thermostability, the enzyme thermal stability system was then used to engineer TlGlu16A through optimization of residual charge-charge interactions. Eleven mutants were constructed and compared to the wild-type TlGlu16A. Four mutants, H58D, E134R, D235G and D296K, showed longer half-life time at 80 °C (31, 7, 25, 22 vs. 0.5 min), and two mutants, D235G and D296K, had greater specific activities (158.2 and 122.2 %, respectively) and catalytic efficiencies (k cat/K m, 170 and 114 %, respectively).

CONCLUSIONS

The engineered TlGlu16A has great application potentials from the perspectives of enzyme yield and properties. Its thermostability and activity were apparently improved in the engineered enzymes through charge optimization. This study spans the genetic, functional and structural fields, and provides a combination of gene mining and protein engineering approaches for the systematic improvement of enzyme performance.

Applications of isothermal titration calorimetry - the research and technical developments from 2011 to 2015

Isothermal titration calorimetry is a widely used biophysical technique for studying the formation or dissociation of molecular complexes. Over the last 5 years, much work has been published on the interpretation of isothermal titration calorimetry (ITC) data for single binding and multiple binding sites. As over 80% of ITC papers are on macromolecules of biological origin, this interpretation is challenging. Some researchers have attempted to link the thermodynamics constants to events at the molecular level. This review highlights work carried out using binding sites characterized using x-ray crystallography techniques that allow speculation about individual bond formation and the displacement of individual water molecules during ligand binding and link these events to the thermodynamic constants for binding. The review also considers research conducted with synthetic binding partners where specific binding events like anion-π and π-π interactions were studied. The revival of assays that enable both thermodynamic and kinetic information to be collected from ITC data is highlighted. Lastly, published criticism of ITC research from a physical chemistry perspective is appraised and practical advice provided for researchers unfamiliar with thermodynamics and its interpretation. Copyright © 2016 John Wiley & Sons, Ltd.

Exchange of active site residues alters substrate specificity in extremely thermostable β-glycosidase from Thermococcus kodakarensis KOD1

β-Glycosidase from Thermococcus kodakarensis KOD1 is a hyperthermophilic enzyme with β-glucosidase, β-mannosidase, β-fucosidase and β-galactosidase activities. Sequence alignment with other β-glycosidases from hyperthermophilic archaea showed two unique active site residues, Gln77 and Asp206. These residues were represented by Arg and Asp in all other hyperthermophilic β-glycosidases. The two active site residues were mutated to Q77R, D206N and D206Q, to study the role of these unique active site residues in catalytic activity and to alter the substrate specificity to enhance its β-glucosidase activity. The secondary structure analysis of all the mutants showed no change in their structure and exhibited in similar conformation like wild-type as they all existed in dimer form in an SDS-PAGE under non-reducing conditions. Q77R and D206Q affected the catalytic activity of the enzyme whereas the D206N altered the catalytic turn-over rate for glucosidase and mannosidase activities with fucosidase activity remain unchanged. Gln77 is reported to interact with catalytic nucleophile and Asp206 with axial C2-hydroxyl group of substrates. Q77R might have made some changes in three dimensional structure due to its electrostatic effect and lost its catalytic activity. The extended side chains of D206Q is predicted to affect the substrate binding during catalysis. The high-catalytic turn-over rate by D206N for β-glucosidase activity makes it a useful enzyme in cellulose degradation at high temperatures.

Destructuring plant biomass: focus on fungal and extremophilic cell wall hydrolases

The use of plant biomass as feedstock for biomaterial and biofuel production is relevant in the current bio-based economy scenario of valorizing renewable resources. Fungi, which degrade complex and recalcitrant plant polymers, secrete different enzymes that hydrolyze plant cell wall polysaccharides. The present review discusses the current research trends on fungal, as well as extremophilic cell wall hydrolases that can withstand extreme physico-chemical conditions required in efficient industrial processes. Secretomes of fungi from the phyla Ascomycota, Basidiomycota, Zygomycota and Neocallimastigomycota are presented along with metabolic cues (nutrient sensing, coordination of carbon and nitrogen metabolism) affecting their composition. We conclude the review by suggesting further research avenues focused on the one hand on a comprehensive analysis of the physiology and epigenetics underlying cell wall degrading enzyme production in fungi and on the other hand on the analysis of proteins with unknown function and metagenomics of extremophilic consortia. The current advances in consolidated bioprocessing, altered secretory pathways and creation of designer plants are also examined. Furthermore, recent developments in enhancing the activity, stability and reusability of enzymes based on synergistic, proximity and entropic effects, fusion enzymes, structure-guided recombination between homologous enzymes and magnetic enzymes are considered with a view to improving saccharification.

The ligninolytic peroxidases in the genus Pleurotus: divergence in activities, expression, and potential applications

Mushrooms of the genus Pleurotus are comprised of cultivated edible ligninolytic fungi with medicinal properties and a wide array of biotechnological and environmental applications. Like other white-rot fungi (WRF), they are able to grow on a variety of lignocellulosic biomass substrates and degrade both natural and anthropogenic aromatic compounds. This is due to the presence of the non-specific oxidative enzymatic systems, which are mainly consisted of lacasses, versatile peroxidases (VPs), and short manganese peroxidases (short-MnPs). Additional, less studied, peroxidase are dye-decolorizing peroxidases (DyPs) and heme-thiolate peroxidases (HTPs). During the past two decades, substantial information has accumulated concerning the biochemistry, structure and function of the Pleurotus ligninolytic peroxidases, which are considered to play a key role in many biodegradation processes. The production of these enzymes is dependent on growth media composition, pH, and temperature as well as the growth phase of the fungus. Mn(2+) concentration differentially affects the expression of the different genes. It also severs as a preferred substrate for these preoxidases. Recently, sequencing of the Pleurotus ostreatus genome was completed, and a comprehensive picture of the ligninolytic peroxidase gene family, consisting of three VPs and six short-MnPs, has been established. Similar enzymes were also discovered and studied in other Pleurotus species. In addition, progress has been made in the development of molecular tools for targeted gene replacement, RNAi-based gene silencing and overexpression of genes of interest. These advances increase the fundamental understanding of the ligninolytic system and provide the opportunity for harnessing the unique attributes of these WRF for applied purposes.

The use of heavy metals in mycoremediation of synthetic dyes

Synthetic dyes represent a major class of toxic pollutants that are resistant to biological degradation, and heavy metals play a special role in this process. In this study, two isolates of lignicolous macromycetes, Lenzites betulina as well as another species less frequently studied, Trametes gibbosa, were tested in order to assess their remediation potential against three different synthetic dyes under specific conditions. The effect of heavy metal ions in the discoloration of synthetic dyes process, and the optimal concentration of manganese ions necessary were evaluated. The dyes’ discoloration efficiency of the fresh isolates were compared to the isolates maintained by refrigeration, isolates that were repeatedly sub-cultivated and isolates that were previously grown on dye-supplemented media, and then were assessed. The discoloration process was evaluated in liquid nutrient media, 10 replicates were used for each working version. Evaluation of discoloration rate was obtained by using a UV-VIS spectrometer. The results were interpreted statistically by the Kruskal-Wallis test and by use of a new complex method, Multiple Factor Analysis. The fresh isolates showed the highest discoloration capacity while the isolates previously grown on the dye-supplemented media presented a low discoloration rate. Manganese ions gave a positive effect on enzyme induction while copper and cobalt ions inhibited the process.

Characterization of combined cross-linked enzyme aggregates from laccase, versatile peroxidase and glucose oxidase, and their utilization for the elimination of pharmaceuticals

In order to transform a wide range of pharmaceutically active compounds (PhACs), the three oxidative enzymes laccase (Lac) from Trametes versicolor, versatile peroxidase (VP) from Bjerkandera adusta and glucose oxidase (GOD) from Aspergillus niger were concomitantly cross-linked after aggregation, thus, making a combined cross-linked enzyme aggregate (combi-CLEA) that was versatile and involved in an enzymatic cascade reaction. From the initial enzymes about 30% of initial laccase activity was recovered along with 40% for each of VP and GOD. The combi-CLEA showed good results in conditions close to those of real wastewater (neutral pH and medium temperature) as well as a good ability to resist to denaturing conditions such as high temperature (60°C) and low pH (3). Batch experiments were realized to test the free enzyme's ability to degrade, a PhACs cocktail, mainly in a synthetic wastewater containing acetaminophen, naproxen, mefenamic acid, indometacin, diclofenac, ketoprofen, caffeine, diazepam, ciprofloxacin, trimethoprim, fenofibrate and bezafibrate, carbamazepine and its by-product 10-11 epoxy-carbamazepine. High removal was achieved (more than 80%) for the five first compounds. Then, the elimination ability of the combi-CLEA with or without hydrogen peroxide, glucose or manganese sulfate was determined. Globally, our results demonstrated that VP has a wider removal spectrum than Lac. These removal features are enhanced under more specific conditions, whereas the combi-CLEA combined advantages of both VP and laccase. Finally, the elimination of PhACs in a municipal wastewater treatment plant effluent using the combi-CLEA was marginally investigated. Concentrations of most of the selected PhACs were below the limit of quantification (lower than 20 ng/L) except for acetaminophen. Its combi-CLEA-mediated removal reached up to 25%.

An intermolecular disulfide bond is required for thermostability and thermoactivity of β-glycosidase from Thermococcus kodakarensis KOD1

Scientists are interested in understanding the molecular origin of protein thermostability and thermoactivity for possible biotechnological applications. The enzymes from extremophilic organisms have been of particular interest in the last two decades. β-glycosidase, Tkβgly is a hyperthermophilic enzyme from Thermococcus kodakarensis KOD1. Tkβgly contains two conserved cysteine residues, C88 and C376. The protein tertiary structure obtained through homology modeling suggests that the C88 residue is located on the surface whereas C376 is inside the protein. To study the role of these cysteine residues, we substituted C88 and C376 with serine residues through site-directed mutagenesis. The wild-type and C376S protein existed in dimeric form and C88S in monomeric form, in an SDS-PAGE gel under non-reducing conditions. Optimal temperature experiments revealed that the wild-type was active at 100 °C whereas the C88S mutant exhibited optimal activity at 70 °C. The half-life of the enzyme at 70 °C was drastically reduced from 266 h to less than 1 h. Although C88 was not present in the active site region, the kcat/Km of C88S was reduced by 2-fold. Based on the structural model and biochemical properties, we propose that C88 is crucial in maintaining the thermostability and thermoactivity of the Tkβgly enzyme.