Reactivity of Pure Candida rugosa Lipase Isoenzymes (Lip1, Lip2, and Lip3) in Aqueous and Organic Media. Influence of the Isoenzymatic Profile on the Lipase Performance in Organic Media

Heterologous expression, purification, and characterization of a recombinant Cordyceps militaris lipase from Candida rugosa-like family in Pichia pastoris

Multiple sequence alignments of three lipase isoforms from the filamentous fungus, Cordyceps militaris, have revealed that the deduced protein from their common sequence belongs to the Candida rugosa lipase-like group. To express the protein in its active form, recombinant lipase from C. militaris (rCML) was extra cellularly expressed in Pichia pastoris X-33 after removing its signal peptide. Purified rCML was a stable monomeric protein with a molecular mass of 90 kDa, and was highly N-mannosylated compared to the native protein (69 kDa). The catalytic efficiency (k_cat/K_m) of rCML was greater than the native protein (1244.35 ± 50.88 and 1067.17 ± 29.07 mM^-1·min^-1, respectively), yet they had similar optimal pH values and temperatures (40 °C and pH 7.0-7.5), and showed preferences for Tween esters and short-chain triacylglycerols. Despite its monomeric conformation, interfacial activation was not observed for rCML, unlike the classical lipases. From the structural model of rCML, the binding pocket of rCML was predicted as a funnel-like structure consisting of a hollow space and an intramolecular tunnel, which is typical of C. rugosa lipase-like lipases. However, a blockage shortened the tunnel to 12-15 Å, which endows strict short-chain selectivity towards triacylglycerols and a perfect match for tricaproin (C6:0). The limited depth of the tunnel may enable accommodation of triacylglycerols with medium-to-long-chain fatty acids, which differentiates rCML from other C. rugosa lipase-like lipases with broad substrate specificities.

Identification and characterization of extracellular enzymes secreted by Aspergillus spp. involved in lipolysis and lipid-antioxidation during katsuobushi fermentation and ripening

A mild-flavored soup stock made from katsuobushi is an important element of traditional Japanese cuisine and is the basic seasoning responsible for the taste. Fermented and ripened katsuobushi, known as karebushi, is manufactured by simmering skipjack tuna that is then smoke-dried, fermented, and ripened in a repeated molding process by five dominant Aspergillus species. Here, our aim was to characterize and identify the lipolytic enzymes secreted by the dominant Aspergillus species, especially A. chevalieri and A. pseudoglaucus, which are involved in hydrolyzing lipids during the molding process. The crude enzyme preparations from the five Aspergillus spp. cultivated on katsuobushi solid medium hydrolyzed triglycerides in fish oil, and more saturated and unsaturated fatty acids (C16:0, C16:1, C18:0, C18:1) were produced than major polyunsaturated fatty acids (C20:5, C22:6). On the basis of ion exchange chromatograms, the composition of the lipolytic enzymes was different in the five species. There was at least one active fraction with high hydrolytic activity toward fish oil in four of the Aspergillus spp., but not A. sydowii; the lipolytic enzyme secreted by A. sydowii had quite high activity toward the artificial substrate p-nitrophenyl butyrate, but low activity toward the natural oil. The lipolytic fractions from A. chevalieri and A. pseudoglaucus were further purified by hydrophobic interaction chromatography then gel-filtration chromatography; LC-MS-MS Mascot analysis identified a variety of lipolytic enzymes, including cutinase, esterase, phospholipase, and carboxyl esterase in the lipolytic fractions from these species. The identified enzymes had 30%-70% identity to previously reported or manually annotated lipases or esterases from taxa other than Aspergillus. The different lipolytic enzymes likely acted on triglycerides in the katsuobushi fish oil. Furthermore, catalase B and Cu/Zn superoxide dismutase, which limit oxidative damage of lipids, were also identified. These antioxidant enzymes may prevent lipid oxidation and rancidity as the lipolytic enzymes hydrolyze lipids during the long fermentation and ripening process. Umami and richness tastes tended to increase in extracts from culture of protease- and peptidase-producing A. sydowii. Our results will aid in the selection and application of desirable strains of Aspergillus species as starter cultures to improve the storage and quality of fermented and ripened karebushi.

Broadband laser-based mid-IR spectroscopy for analysis of proteins and monitoring of enzyme activity

Laser-based infrared (IR) spectroscopy is an emerging key technology for the analysis of solutes and for real-time reaction monitoring in liquids. Larger applicable pathlengths compared to the traditional gold standard Fourier transform IR (FTIR) spectroscopy enable robust measurements of analytes in a strongly absorbing matrix such as water. Recent advancements in laser development also provide large accessible spectral coverage thus overcoming an inherent drawback of laser-based IR spectroscopy. In this work, we benchmark a commercial room temperature operated broadband external cavity-quantum cascade laser (EC-QCL)-IR spectrometer with a spectral coverage of 400 cm^-1 against FTIR spectroscopy and showcase its application for measuring the secondary structure of proteins in water, and for monitoring the lipase-catalyzed saponification of triacetin. Regarding the obtained limit of detection (LOD), the laser-based spectrometer compared well to a research-grade FTIR spectrometer employing a liquid nitrogen cooled detector. With respect to a routine FTIR spectrometer equipped with a room temperature operated pyroelectric detector, a 15-fold increase in LOD was obtained in the spectral range of 1600-1700 cm^-1. Characteristic spectral features in the amide I and amide II region of three representative proteins with different secondary structures could be measured at concentrations as low as 0.25 mg mL^-1. Enzymatic hydrolysis of triacetin by lipase was monitored, demonstrating the advantage of a broad spectral coverage for following complex chemical reactions. The obtained results in combination with the portability and small footprint of the employed spectrometer opens a wide range of future applications in protein analysis and industrial process control, which cannot be readily met by FTIR spectroscopy without recurring to liquid nitrogen cooled detectors.

Versatile Lipases from the Candida rugosa-like Family: A Mechanistic Insight Using Computational Approaches

Lipases are enzymes able to catalyze the hydrolysis or synthesis of triglycerides, depending on the reaction conditions, whereas sterol esterases show the same ability on sterol esters. Structurally, both kinds of enzymes display an α/β-hydrolase fold, with a substrate-binding pocket formed by a hydrophobic cavity covered by a mobile lid. However, it has been reported that some lipases from the Candida rugosa-like family display wide substrate specificity on both triglycerides and sterol esters. Among them, enzymes with different biotechnological applications, such as the lipase isoenzymes produced by C. rugosa and the sterol esterase from Ophiostoma piceae, have been exhaustively characterized and their crystal structures are available. Differences in substrate affinity among these proteins have been attributed to changes in their hydrophobicity. In this work, we analyzed the full catalytic mechanisms of these proteins using molecular dynamics tools, gaining insight into their mechanistic properties. In addition, we developed an in silico protocol to predict the substrate specificity using C. rugosa and O. piceae lipases as model enzymes and triglycerides and cholesterol esters with different fatty acid chain lengths as model substrates. The protocol was validated by comparing the in silico results with those described in the literature. These results would be useful to perform virtual screening of substrates for enzymes of the C. rugosa-like family with unknown catalytic properties.

Immobilization of Candida rugosa lipase for resolution of racimic ibuprofen

AIM

Due to lipases' regio-selectivity and ability to catalyze different reactions such as hydrolysis, esterification, and transesterification, the enzyme is attractive in biotransformation technology. Besides, another technology, namely enzyme immobilization, has attracted scientists/technologists' attention to employ immobilized lipase in such a field. Thus lipase of Candida rugosa was immobilized onto silica nanoparticles through adsorption. Furthermore, the immobilized biocatalyst was characterized and used to esterify ibuprofen enantioselectively.

METHODS

To characterize immobilized lipase onto silica nanoparticles scanning electron microscopy (SEM) and dynamic light scattering (DLS) were used.

RESULTS

The catalytic properties of both immobilized and free lipases such as optima pH and temperature were not different. According to the results, the immobilized lipase on silica nanoparticles showed 45% and 96% conversion (C) and enantioselectivity (ee_s), respectively. In comparison to free lipase, the immobilized enzyme came with better catalytic activity.

CONCLUSION

Silica nanoparticles as one of the most promising materials for the immobilization of lipase in enantioselective esterification of ibuprofen, were introduced in this work.

Immobilisation of Candida rugosa lipase on a highly hydrophobic support: A stable immobilised lipase suitable for non-aqueous synthesis

Lipase from Candida rugosa (CrL) was immobilised on highly hydrophobic, octadecyl methacrylate resin (Lifetech™ ECR8806M) via interfacial adsorption. The aim was to produce a stable biocatalyst suitable for use in a range of lipid-modifying reactions. Immobilisation was carried out in 10 mM phosphate buffer (pH 6.0) over 24 h at 21 °C. High protein binding of 58.7 ± 4.9 mg/g dry support accounted for ∼53 % of the applied protein. The activity recovery against tributyrin was 74.0 ± 1.1 %. The specific activity of immobilised CrL against tributyrin was considerably higher than that of Novozym® 435, at 1.79 ± 0.05 and 1.08 ± 0.04 U/mg bound protein, respectively. Incubation with high concentrations (10 % w/v) of both Triton X-100 and SDS resulted in only a small reduction in immobilised lipase activity. Solvent-free synthesis of glycerides by the FFA-saturated immobilised CrL was successful over 6 reaction cycles, with no apparent loss of activity.

Amphipathic Janus Membrane with Hierarchical Multiscale Hyperporous Structure for Interfacial Catalysis

The rational design and realization of multiscale porous structures has been a long-standing challenge in membrane science. Block copolymers (BCPs) with their self-assembly-enabled nanodomains have the potential to make structural breakthroughs. An amphipathic Janus membrane, with a hierarchical multiscale hyperporous structure constituted by polystyrene-b-poly(4-vinylpyridine) (PS4VP) and polyvinylidene fluoride (PVDF) blocks, was designed and synthesized in this work. Hydrophobic PVDF dominated one side of the membrane, and hydrophilic PS4VP, with nanopores that formed inside the macroporous channels of PVDF via a self-assembly approach, dominated the other side. Candida Rugosa Lipase (CRL), as a model biocatalyst, was immobilized in the PS4VP nanopores via injection. The immobilized lipase was exactly suspended at the interface of the organic and aqueous phases, owing to the amphipathic property of the Janus membrane. The designed structures and catalysis performances were further characterized. The immobilized lipase exhibited a three times higher specific activity than free lipase, and the relative activity still remained above 90% after 10 cycles of reusing, indicating the observable promotion and the guaranteed stability of the Janus membrane in interfacial catalysis. This work provided a general, facile and unique example for the design and synthesis of a hierarchical multiscale hyperporous membrane for interfacial catalysis.

Surface-Displayed Thermostable Candida rugosa Lipase 1 for Docosahexaenoic Acid Enrichment

Yeast surface display has emerged as a viable approach for self-immobilization enzyme as whole-cell catalysts. Herein, we displayed Candida rugosa lipase 1 (CRL LIP1) on the cell wall of Pichia pastoris for docosahexaenoic acid (DHA) enrichment in algae oil. After a 96-h culture, the displayed CRL LIP1 achieved the highest activity (380 ± 2.8 U/g) for hydrolyzing olive oil under optimal pH (7.5) and temperature (45 °C) conditions. Additionally, we improved the thermal stability of displayed LIP1, enabling retention of 50% of its initial bioactivity following 6 h of incubation at 45 °C. Furthermore, the content of DHA enhanced from 40.61% in original algae oil to 50.44% in glyceride, resulting in a 1.24-fold increase in yield. The displayed CRL LIP1 exhibited an improved thermal stability and a high degree of bioactivity toward its native macromolecule substrates algae oil and olive oil, thereby expanding its potential for industrial applications in fields of food and pharmaceutical. These results suggested that surface display provides an effective strategy for simultaneous convenient expression and target protein immobilization.

Contribution of the Oligomeric State to the Thermostability of Isoenzyme 3 from Candida rugosa

Thermophilic proteins have evolved different strategies to maintain structure and function at high temperatures; they have large, hydrophobic cores, and feature increased electrostatic interactions, with disulfide bonds, salt-bridging, and surface charges. Oligomerization is also recognized as a mechanism for protein stabilization to confer a thermophilic adaptation. Mesophilic proteins are less thermostable than their thermophilic homologs, but oligomerization plays an important role in biological processes on a wide variety of mesophilic enzymes, including thermostabilization. The mesophilic yeast Candida rugosa contains a complex family of highly related lipase isoenzymes. Lip3 has been purified and characterized in two oligomeric states, monomer (mLip3) and dimer (dLip3), and crystallized in a dimeric conformation, providing a perfect model for studying the effects of homodimerization on mesophilic enzymes. We studied kinetics and stability at different pHs and temperatures, using the response surface methodology to compare both forms. At the kinetic level, homodimerization expanded Lip3 specificity (serving as a better catalyst on soluble substrates). Indeed, dimerization increased its thermostability by more than 15 °C (maximum temperature for dLip3 was out of the experimental range; >50 °C), and increased the pH stability by nearly one pH unit, demonstrating that oligomerization is a viable strategy for the stabilization of mesophilic enzymes.

Oil type and cross-linking influence growth of Aureobasidium melanogenum on vegetable oils as a single carbon source

Aureobasidium melanogenum is the main fungus found in a spontaneously formed biofilm on a oil‐treated wood. This dark colored biofilm functions as a protective coating. To better understand biofilm formation, in this study A. melanogenum was cultured on olive oil and raw linseed oil. Metabolic activity and oil conversion were measured. The results show that A. melanogenum is able to grow on linseed oil and olive oil as a single carbon source. The fungus produces the enzyme lipase to convert the oil into fatty acids and glycerol. Metabolic activity and oil conversion were equal on linseed oil and olive oil. The fungus was not able to grow on severe cross‐linked linseed oil, meaning that the degree of cross‐linking of the oil is important for growth of A. melanogenum. Dark coloring of the colony was seen on linseed oil, which might be a stress response on the presence of autoxidation products in linseed oil. The colony on olive oil showed delayed melanin production indicating an inhibitory effect of olive oil on melanin production.

Identification of a hot-spot to enhance Candida rugosa lipase thermostability by rational design methods

Lipase is one of the most widely used classes of enzymes in biotechnological applications and organic chemistry. Candida rugosa lipases (CRL) can catalyze hydrolysis, esterification and transesterification with high regio-, stereo- and enantio-selectivity. However, thermal inactivation above 45 °C limits CRL's applications. Studies on improving the thermal stability of CRL are often limited by its slow-growing eukaryotic expression host, which is not suitable for large-scale screening. Identification of thermally stable mutants by rational design, regarded as an efficient substitution of experimental efforts, would provide a method for site-directed improvement of CRL. In this study, mutation-induced stability changes in CRL Lip1 were predicted by three rational design methods. Followed by conservative analyses and functional region exclusion, five mutants of a hot-spot, Asp457Phe, Asp457Trp, Asp457Met, Asp457Leu, and Asp457Tyr, were identified and prepared for enzymatic characterization. These five mutants increased the apparent melting temperature of Lip1 from 7.4 °C to 9.3 °C, with the most thermostable mutant, Asp457Phe, exhibiting a 5.5-fold longer half-life at 50 °C and a 10 °C increase in optimum temperature. Furthermore, pH stability of Lip1 was also enhanced due to the introduction of Asp457Phe mutation. The study demonstrates that thermally stable mutants of CRL could be identified with limited experimental efforts using rational design methods.

The thermostability of Candida rugosa lipase expressed in a eukaryotic host is enhanced with limited experimental effort based on rational design methods.

Cross-linked enzyme aggregates (CLEAs) of selected lipases: a procedure for the proper calculation of their recovered activity

In the last few years, synthesis of carrier-free immobilized biocatalysts by cross-linking of enzyme aggregates has appeared as a promising technique. Cross-linked enzyme aggregates (CLEAs) present several interesting advantages over carrier-bound immobilized enzymes, such as highly concentrated enzymatic activity, high stability of the produced superstructure, important production costs savings by the absence of a support, and the fact that no previous purification of the enzyme is needed. However, the published literature evidences that a) much specific non-systematic exploratory work is being done and, b) recovered activity calculations in CLEAs still need to be optimized. In this context, this contribution presents results of an optimized procedure for the calculation of the activity retained by CLEAs, based on the comparison of their specific activity relative to their free enzyme counterparts. The protocol implies determination of precipitable protein content in commercial enzyme preparations through precipitation with ammonium sulphate and a protein co-feeder. The identification of linear ranges of activity versus concentration/amount of protein in the test reaction is also required for proper specific activity determinations. By use of mass balances that involve the protein initially added to the synthesis medium, and the protein remaining in the supernatant and washing solutions (these last derived from activity measurements), the precipitable protein present in CLEAs is obtained, and their specific activity can be calculated. In the current contribution the described protocol was applied to CLEAs of Thermomyces lanuginosa lipase, which showed a recovered specific activity of 11.1% relative to native lipase. The approach described is simple and can easily be extended to other CLEAs and also to carrier-bound immobilized enzymes for accurate determination of their retained activity.

Effect of Additives and Process Variables on Enzymatic Hydrolysis of Macauba Kernel Oil (Acrocomia aculeata)

This work investigates the production of free fatty acids (FFAs) from the enzymatic hydrolysis of macauba kernel oil. Experiments evaluate the effect of different enzymes and the addition of salts, surfactants, and solvents to the reaction medium, as well as the effect of process variables. Results showed that FFA yields obtained for use of Lipozyme RM IM were higher than those obtained from Lipozyme TL IM and Lipozyme 435. The addition of salts and surfactants did not promote increased production of FFAs, while addingn-hexane and heptane to the reaction medium led to an increased reaction rate. It can be observed for the results that the temperature, water :  oil mass ratio, and enzyme percentage had positive effects on the FFA yield in the range of 35°C to 55°C, 1 :  20 to 1 :  2, and 1 to 15%, respectively, and that, from these limits, increases in these variables did not cause significant increase in FFA yields. The addition of buffer promoted an increase in yield FFAs, as well as the pH of the buffer, and it was reported that an agitation of 400 rpm resulted in the highest yields in the investigated range.

New tools for exploring "old friends-microbial lipases"

Fat-splitting enzymes (lipases), due to their natural, industrial, and medical relevance, attract enough attention as fats do in our lives. Starting from the paper that we write, cheese and oil that we consume, detergent that we use to remove oil stains, biodiesel that we use as transportation fuel, to the enantiopure drugs that we use in therapeutics, all these applications are facilitated directly or indirectly by lipases. Due to their uniqueness, versatility, and dexterity, decades of research work have been carried out on microbial lipases. The hunt for novel lipases and strategies to improve them continues unabated as evidenced by new families of microbial lipases that are still being discovered mostly by metagenomic approaches. A separate database for true lipases termed LIPABASE has been created recently which provides taxonomic, structural, biochemical information about true lipases from various species. The present review attempts to summarize new approaches that are employed in various aspects of microbial lipase research, viz., screening, isolation, production, purification, improvement by protein engineering, and surface display. Finally, novel applications facilitated by microbial lipases are also presented.

Recombinant sterol esterase from Ophiostoma piceae: an improved biocatalyst expressed in Pichia pastoris

BACKGROUND

The ascomycete Ophiostoma piceae produces a sterol esterase (OPE) with high affinity towards p-nitrophenol, glycerol and sterol esters. Its hydrolytic activity on natural mixtures of triglycerides and sterol esters has been proposed for pitch biocontrol in paper industry since these compounds produce important economic losses during paper pulp manufacture.

RESULTS

Recently, this enzyme has been heterologously expressed in the methylotrophic yeast Pichia pastoris, and the hydrolytic activity of the recombinant protein (OPE*) studied. After the initial screening of different clones expressing the enzyme, only one was selected for showing the highest production rate. Different culture conditions were tested to improve the expression of the recombinant enzyme. Complex media were better than minimal media for production, but in any case the levels of enzymatic activity were higher (7-fold in the best case) than those obtained from O. piceae. The purified enzyme had a molecular mass of 76 kDa, higher than that reported for the native enzyme under SDS-PAGE (60 kDa). Steady-state kinetic characterization of the recombinant protein showed improved catalytic efficiency for this enzyme as compared to the native one, for all the assayed substrates (p-nitrophenol, glycerol, and cholesterol esters). Different causes for this were studied, as the increased glycosylation degree of the recombinant enzyme, their secondary structures or the oxidation of methionine residues. However, none of these could explain the improvements found in the recombinant protein. N-terminal sequencing of OPE* showed that two populations of this enzyme were expressed, having either 6 or 8 amino acid residues more than the native one. This fact affected the aggregation behaviour of the recombinant protein, as was corroborated by analytical ultracentrifugation, thus improving the catalytic efficiency of this enzyme.

CONCLUSION

P. pastoris resulted to be an optimum biofactory for the heterologous production of recombinant sterol esterase from O. piceae, yielding higher activity levels than those obtained with the saprophytic fungus. The enzyme showed improved kinetic parameters because of its modified N-terminus, which allowed changes in its aggregation behaviour, suggesting that its hydrophobicity has been modified.

Optimization of process parameters influencing the submerged fermentation of extracellular lipases from Pseudomonas aeruginosa, candida albicans and Aspergillus flavus

The present study was aimed at optimization, production and partial purification of lipases from Pseudomonas aeruginosa, Candida albicans and Aspergillus flavus. Various nutritional and physical parameters affecting lipase production such as carbon and nitrogen supplements, pH, temperature, agitation speed and incubation time were studied. Refined sunflower oil (1% v/v) and tryptone at a pH of 6.2 favored maximum lipase production in Pseudomonas at 30 degrees C and 150 rpm, when incubated for 5 days. In C. albicans refined sunflower oil (3% v/v) and peptone resulted in maximum lipase production at pH 5.2, 30 degrees C and 150 rpm, when incubated for 5 days. In A. flavus coconut oil (3% v/v) and peptone yielded maximum lipase at pH 6.2, 37 degrees C, 200 rpm after an incubation period of 5 days. The lipases were partially purified by ammonium sulphate precipitation and dialysis. In P. aeruginosa enzyme activity of the dialyzed fraction was found to be 400 U mL-' and for C. albicans 410 U mL(-1). The dialysed lipase fraction from A. flavus demonstrated an activity of 460 U mL(-1). The apparent molecular weights of the dialyzed lipases were determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The dialyzed lipase fraction obtained from P. aeruginosa revealed molecular weights of 47, 49 and 51 kDa, whereas, lipases from C. albicans and A. flavus demonstrated 3 bands (16.5, 27 and 51 kDa) and one band (47 kDa), respectively. These extracellular lipases may find wide industrial applications.

Lipases: an overview

Lipases are ubiquitous enzymes, widespread in nature. They were first isolated from bacteria in the early nineteenth century and the associated research continuously increased due to the particular characteristics of these enzymes. This chapter reviews the main sources, structural properties, and industrial applications of these highly studied enzymes.

Production of lipases by solid state fermentation using vegetable oil-refining wastes

Lipases were produced by a microbial consortium derived from a mixture of wastewater sludges in a medium containing solid industrial wastes rich in fats, under thermophilic conditions (temperature higher than 45°C for 20 days) in 4.5-L reactors. The lipases were extracted from the solid medium using 100mM Tris-HCl, pH 8.0 and a cationic surfactant agent (cetyltrimethylammonium chloride). Different doses of surfactant and buffer were tested according to a full factorial experimental design. The extracted lipases were most active at 61-65°C and at pH 7.7-9. For the solid samples, the lipolytic activity reached up to 120,000 UA/g of dry matter. These values are considerably higher than those previously reported in literature for solid-state fermentation and highlight the possibility to work with the solid wastes as effective biocatalysts.

Production and use of lipases in bioenergy: a review from the feedstocks to biodiesel production

Lipases represent one of the most reported groups of enzymes for the production of biofuels. They are used for the processing of glycerides and fatty acids for biodiesel (fatty acid alkyl esters) production. This paper presents the main topics of the enzyme-based production of biodiesel, from the feedstocks to the production of enzymes and their application in esterification and transesterification reactions. Growing technologies, such as the use of whole cells as catalysts, are addressed, and as concluding remarks, the advantages, concerns, and future prospects of enzymatic biodiesel are presented.

Engineering the expression and biochemical characteristics of recombinant Candida rugosa LIP2 lipase by removing the additional N-terminal peptide and regional codon optimization

Candida rugosa lipase (CRL), an important industrial enzyme, has been established, containing several different isoforms which were encoded by the high-identity lip gene family (lip1 to lip7). In this study, we compared the expression and biochemical characterization with three different engineered lip2 constructions in the yeast Pichia pastoris. Our results showed that lip2 (lip2) has an overall improvement of 50% higher production yield (1.446 U/mL) relative to that of nflip2 (0.964 U/mL) at 7 days of cultivation time. Codon-optimized lip2 (colip2) has a 2.3-fold higher production yield (2.182 U/mL) compared to that of lip2 (noncodon-optimized; 1.446 U/mL) and nflip2 (0.964 U/mL), with a cultivation time of 5 days. This finding demonstrated that the removal of the N-terminus and the regional codon optimization of the lip2 gene fragment at the 5' end can greatly increase the expression level of recombinant LIP2 in the P. pastoris system. The distinct biochemical properties of our purified recombinant nfLIP2 and LIP2 suggested that they are potentially useful for various industrial applications.

Preparation and characterization of single-enzyme nanogels

Enzymes have been incorporated in nanostructures in order to provide robust catalysts for valuable reactions, particularly those performed under harsh and denaturing conditions. This chapter describes the encapsulation of enzymes in polyacrylamide nanogels by a two-step in situ polymerization process for preparing robust biocatalysts. The first step in this process is the generation of vinyl groups on the enzyme surface, while the second step involves in situ polymerization using acrylamide as the monomer. Encapsulation of the enzyme in the hydrophilic, porous, and flexible polyacrylamide gel of several nanometers thick would help to both give a significantly enhanced thermostability and prevent the removal of essential water by polar solvents. The hydrophilic flexible polymer shell also allows the protein structure to undergo necessary conformational transitions during the catalytic reaction and, at the same time, impose marginal mass transfer restrictions for the substrates entering across the polymer shell. The effectiveness of this method is demonstrated with horseradish peroxidase (HRP), carbonic anhydrase, and lipase. The impacts of such an encapsulation on the activity and stability of enzymes are also discussed.

Impact of inoculation strategy on the progress of Candida rugosa cultivation

Batch cultivation of Candida rugosa for the production of lipase and esterase enzymes was carried out by employing two different inoculation strategies. The effects of triolein (2, 3 and 5 g/l) and oleic acid (3 g/l) as carbon sources of the enzyme production medium on the activity, productivity, and yield of enzymes were also compared for both strategies. Inoculation of the cells into the enzyme production medium either directly or after cultivation in a pre-culture medium rich in glucose affected the activity and yield of esterase more than those of lipase for both carbon sources. In both strategies, triolein and oleic acid yielded the same lipase activity (16.67 U/ml) whereas triolein provided higher esterase activity (0.0035 U/ml). Time courses of the extracellular and intracellular lipase and esterase enzymes indicated that lipase activity was growth-associated and the cells secreted esterase into the medium after a considerable level of extracellular lipase activity was reached. The role of protease in the enzyme activities was also discussed.

Molecular fundamentals of enzyme nanogels

The assembly of a monomer around an enzyme as the essential step in the fabrication of enzyme nanogel by in situ polymerization was illustrated by molecular dynamics simulation and evidenced by a fluorescence resonance energy transfer spectrum, using lipase/acrylamide as a model system. The subsequent polymerization generated a hydrophilic gel network which not only strengthened the protein structural integrity via multipoint linkage but also increased the number of intramolecular H-bonds of the encapsulated protein, as suggested by the blue shift of the fluorescence spectrum of the encapsulated lipase. This greatly enhanced the stability of lipase at high temperature, as experimentally demonstrated. The exclusion of polar solvent molecules from the encapsulated enzyme, in contrast to the enrichment of water molecules, due to the presence of a hydrophilic gel network was displayed. This established a hydrophilic microenvironment for the encapsulated protein and thus gave the encapsulated protein an enhanced tolerance to the organic solvent, as experimentally observed in the present study and reported elsewhere. These results have given a molecular insight into the enzyme nanogel as well as its high potential as a robust enzyme model for an expended application spectrum of enzymatic catalysis.