The lid is a structural and functional determinant of lipase activity and selectivity

Decreasing acid value of fatty acid ethyl ester products using complex enzymes

Recently, enzymatic method has been used to prepare biodiesel using various oils. But the high acid value of the biodiesel product using enzyme as a catalyst has been one issue. In this work, an attempt to reduce the acid value of fatty acid ethyl ester (FAEE) product to satisfy the specified requirement (AV ≤ 0.5 mgKOH/g), a complex enzyme-catalyzed method was used for the ethanolysis of Semen Abutili seed oil (SASO) (AV = 5.5 ± 0.3 mgKOH/g). The effects of various variables (constituents of complex enzyme, type and addition of water removal agent, time, temperature, enzyme addition load, substrate ratio) on the enzymatic reaction were investigated. The optimal reaction conditions were: 1% addition of liquid lipase Eversa® Transform 2.0% and 0.8% of enzyme dry powder CALB, reaction temperature 35°C, alcohol-oil ratio 9:1 (mol/mol), 0.8 g/g of 4A-MS and reaction time 24 h. Under the optimal reaction conditions, the FAEE yield was 90.8% ± 1.5% and its acid value was decreased from 12.0 ± 0.2 mgKOH/g to 0.39 ± 0.10 mgKOH/g. In further evaluating the feasibility of preparing FAEE from SASO, the FAEE products obtained under the optimal reaction conditions were purified and evaluated with reference to the ASTM D6751 standard for the main physicochemical indexes. The results obtained were in accordance with the requirements except for the oxidative stability.

Structure-directed bioengineering the lid1 of cold-adapted Pseudomonas sp. TB11 esterase to boost catalytic capacity

Structure-guided bioengineering enzymes has been an efficient strategy to obtain biocatalyst with desirable properties. In this study, the cold-adapted esterase from Pseudomonas sp. (CPE) was optimized through bioinformatic-based structured-guided bioengineering on lid1 region. Substitutions of non-conserved Q55 led to noticeable increase in hydrolysis without sacrificing enzyme thermostability, activating effects of Ca2+ and organic solvents. Compared to the wild type, both of Q55V and Q55N among the constructed variants exhibited about a 2.0-fold and 6.5-fold higher hydrolytic activity toward short-chain and long-chain substrates, respectively. In contrast, lid swapping with the lid of Thermomyces lanuginosus lipase reduced the activity and thermostability of CPE. Catalytic kinetics revealed that substitution of Q55 with Y, V, N and R enhanced the substrate affinity of CPE. Hydrolysis by Q55V remarkedly enriched the characteristic flavor components of single cream. The study sheds light on structure-guided bioengineering of lid tailoring cold-adapted esterases with desired catalytic performance to meet the demand from biotechnological applications.

Surfactant-based metal-organic frameworks (MOFs) in the preparation of an active biocatalysis

Metal-organic frameworks (MOFs) are used as ideal support materials thanks to their unique properties and have become the focus of interest in enzyme immobilization studies, especially in recent years. In order to increase the catalytic activity and stability of Candida rugosa lipase (CRL), a new fluorescence-based MOF (UiO-66-Nap) derived from UiO-66 was synthesized. The structures of the materials were confirmed by spectroscopic techniques such as FTIR, ¹H NMR, SEM, and PXRD. CRL was immobilized on UiO-66-NH₂ and UiO-66-Nap by adsorption technique and immobilization and stability parameters of UiO-66-Nap@CRL were examined. Immobilized lipases UiO-66-Nap@CRL exhibited higher catalytic activity (204 U/g) than UiO-66-NH₂@CRL (168 U/g), which indicates that the immobilized lipase (UiO-66-Nap@CRL) carries sulfonate groups, this is due to strong ionic interactions between the surfactant's polar groups and certain charged locations on the protein surface. The Free CRL lost its catalytic activity completely at 60 °C after 100min, while UiO-66-NH₂@CRL and UiO-66-Nap@CRL retained 45% and 56% of their catalytic activity at the end of 120min, respectively. After 5 cycles, the activity of UiO-66-Nap@CRL remained 50%, while the activity of UiO-66-NH₂@CRL was about 40%. This difference is due to the surfactant groups (Nap) in UiO-66-Nap@CRL. These results show that the newly synthesized fluorescence-based MOF derivative (UiO-66-Nap) can be an ideal support material for enzyme immobilization and can be used successfully to protect and increase the activities of enzymes.

A comprehensive review on the pancreatic lipase inhibitory peptides: A future anti-obesity strategy

Dysregulation of lipid homeostasis contributes to obesity and can directly lead to several critical public health concerns globally. This paper aimed to present a brief review of related properties and the use of pancreatic lipase inhibitors as the future weight loss drug discovery and development procured from a wide range of natural sources. A total of 176 pancreatic lipase inhibitory peptides were identified from recent publications and peptide databases. These peptides were classified into three categories according to their peptide length and further analyzed using bioinformatic approaches to identify their structural activity relationship. Molecular docking analyses were conducted for each amino acid at the terminal position of the peptides to predict the binding affinity between peptide-enzyme protein complexes based on intermolecular contact interactions. Overall, the observations revealed the features of the inhibitory peptides and their inhibitory mechanisms and interactions. These findings strived to benefit scientists whose research may be relevant to anti-obesity drug development and/or discovery thereby support effective translation of preclinical research for humans’ health being.

Structural dynamics and mechanistic action guided engineering of lipolytic enzymes

Lipases have been established as important biocatalysts in several industrial applications, owing to their diverse substrate specificity. The availability of data on three-dimensional crystal structures for various lipases offers an opportunity for modulating their structural and functional aspects to design and engineer better versions of lipases. With the aim of investigating the structural components governing the extremophilic behavior of lipases, structural analysis of microbial lipases was performed using advanced bioinformatics and molecular dynamics simulation approaches. In sequences and functionally distinct alkaliphilic and thermophilic lipases were investigated for their functional properties to understand the distinguishing features of their structures. The alkaliphilic lipase from Bacillus subtilis (LipA) showed conformational changes in the loop region Ala132-Met137, subsequently, the active site residue His156 shows two conformations, toward the active site nucleophilic residues Ser77 and away from the Ser77. Interestingly, the active site of LipA is more solvent-exposed and can be correlated with the adoption of an open conformation which might extend and expose the active site region to solvents during the catalysis process. Furthermore, the MD simulation of thermophilic lipase from marine Streptomyces (MAS1) revealed the role of N- and C-terminal regions with disulfide bridges and identified a metal ion binding site that facilitates the enzyme stability. The novel thermo-alkaliphilic lipase can be designed to integrate the stability features of MAS1 into the alkaliphilic LipA. These structural-level intrinsic characteristics can be used for lipase engineering to amend the lipase activity and stability as per the requirements of the industrial processes.

Single-Particle Tracking of Thermomyces lanuginosus Lipase Reveals How Mutations in the Lid Region Remodel Its Diffusion

The function of most lipases is controlled by the lid, which undergoes conformational changes at a water–lipid interface to expose the active site, thus activating catalysis. Understanding how lid mutations affect lipases’ function is important for designing improved variants. Lipases’ function has been found to correlate with their diffusion on the substrate surface. Here, we used single-particle tracking (SPT), a powerful tool for deciphering enzymes’ diffusional behavior, to study Thermomyces lanuginosus lipase (TLL) variants with different lid structures in a laundry-like application condition. Thousands of parallelized recorded trajectories and hidden Markov modeling (HMM) analysis allowed us to extract three interconverting diffusional states and quantify their abundance, microscopic transition rates, and the energy barriers for sampling them. Combining those findings with ensemble measurements, we determined that the overall activity variation in the application condition is dependent on surface binding and lipase mobility when bound. Specifically, the L4 variant with a TLL-like lid and wild-type (WT) TLL displayed similar ensemble activity, but WT bound stronger to the surface than L4, while L4 had a higher diffusion coefficient and thus activity when bound to the surface. These mechanistic elements can only be de-convoluted by our combined assays. Our findings offer fresh perspectives on the development of the next iteration of enzyme-based detergent.

The High ‘Lipolytic Jump’ of Immobilized Amano A Lipase from Aspergillus niger in Developed ‘ESS Catalytic Triangles’ Containing Natural Origin Substrates

Lipase Amano A from Aspergillus niger (AA-ANL) is among the most commonly applied enzymes in biocatalysis processes, making it a significant scientific subject in the pharmaceutical and medical disciplines. In this study, we investigated the lipolytic activity of AA-ANL immobilized onto polyacrylic support IB-150A in 23 oils of natural origin containing various amounts of polyunsaturated fatty acids (PUFAs) and monounsaturated fatty acids (MUFAs). The created systems were expressed as an ‘ESS catalytic triangle’. A distinct ‘jump’ (up to 2400%) of lipolytic activity of immobilized AA-ANL compared to free lipase and hyperactivation in mostly tested substrates was observed. There was a ‘cutoff limit’ in a quantitative mutual ratio of ω-PUFAs/MUFAs, for which there was an increase or decrease in the activity of the immobilized AA-ANL. In addition, we observed the beneficial effect of immobilization using three polyacrylic supports (IB-150A, IB-D152, and IB-EC1) characterized by different intramolecular interactions. The developed substrate systems demonstrated considerable hyperactivation of immobilized AA-ANL. Moreover, a ‘lipolytic jump’ in the full range of tested temperature and pH was also observed. The considerable activity of AA-ANL-IB-150A after four reuse cycles was demonstrated. On the other hand, we observed an essential decrease in stability of immobilized lipase after 168 h of storage in a climate chamber. The tested kinetic profile of immobilized AA-ANL confirmed the increased affinity to the substrate relative to lipase in the free form.

Possible Charged Residue Switch for Acylglycerol Selectivity of Lipase MAS1

The amino acid residues lining the substrate binding pocket play quite an important role during the lipase catalytic process. The conversion of those residues might cause a dramatic change in the lipase properties, such as the substrate selectivity of lipase. In our study, T237 residue sitting on the entrance of the catalytic pocket in lipase MAS1 was important for the catalytic performance. When replacing polar Thr with the positively charged Arg, the synthesis ratio of partial glycerides/triglycerides increases to 6.32 rather than 1.21 of MAS1 wild type (WT), as the substrate ratio of glycerol and fatty acids is 1:3. And the fatty acid preference shifted to long-chain substrates for mutant T237R rather than middle-chain substrates for MAS1 WT. Molecular docking analysis revealed that hydrophobic and side chain properties of Arg might contribute to the change of the MAS1 lipase catalytic performance. This work would pave a way for the accurate rational transformation of the lipases to produce value lipid for industrial application.

Lipase immobilization on a novel class of Zr-MOF/electrospun nanofibrous polymers: Biochemical characterization and efficient biodiesel production

In this study, due to the favorable properties of MOF compounds and fibrous materials, new nanostructures of Zr-MOF/PVP nanofibrous composites were synthesized by electrospinning procedure. The related features of these samples were characterized by relevant analyzes, including SEM, BET surface area analysis, XRD, and FTIR spectroscopy. The final product showed significant properties such as small particle size distribution, large surface area, and high crystallinity. This strategy for producing these nanostructures could lead to new compounds as novel alternative materials for biological applications. Lipase MG10 was successfully immobilized on the mentioned nanofibrous composites and biochemically characterized. The lipase activity of free and immobilized lipases was considered by measuring the absorbance of pNPP (500 μM in 40 mM Tris/HCl buffer, pH 7.8, and 0.01% Triton X100) at 37 °C for 30 min. Different concentrations of glutaraldehyde, different crosslinking times, different times of immobilization, different enzyme loading, and different pH values have been optimized. Results showed that the optimized immobilization condition was achieved in 2.5% glutaraldehyde, after 2 h of crosslinking time, after 6 h immobilization time, using 180 mg protein/g support at pH 9.0. The immobilized enzyme was also totally stable after 180 min incubation at 60 °C. The free enzyme showed the maximum activity at pH 9.0, but the optimal pH of the immobilized lipase was shifted about 1.5 pH units to the alkaline area. The immobilized lipase showed about 2.7 folds (78%) higher stability than the free enzyme at 50 °C. Some divalent metal ions, including Cu²⁺ (22%), Co²⁺ (37%), Mg²⁺ (12%), Hg²⁺ (11%), and Mn²⁺ (17%) enhanced the enzyme activity of immobilized enzyme. The maximum biodiesel production (27%) from R. communis oil was obtained after 18 h of incubation by lipase MG10. The immobilized lipase displayed high potency in biodiesel production, about 83% after 12 h of incubation. These results indicated the high potency of Zr-MOF/PVP nanofibrous composites for efficient lipase immobilization.

Optimization of Spectrophotometric and Fluorometric Assays Using Alternative Substrates for the High-Throughput Screening of Lipase Activity

The effects of reaction conditions on the spectrophotometric and fluorometric assays using alternative substrates (p-nitrophenyl palmitate and 4-methylumbelliferyl oleate) were investigated to optimize them for the high-throughput screening of lipase activity from agricultural products. Four model lipases from Chromobacterium viscosum, Pseudomonas fluorescens, Sus scrofa pancreas, and wheat germ (Triticum aestivum) were allowed to hydrolyze the alternative substrates at different substrate concentrations (1–5 mM), operating pH (5.0–8.0), and operating temperatures (25–55°C). The results show that both the spectrophotometric and fluorometric assays worked well at the standard reaction conditions (pH 7.0 and 30°C) for finding a typical lipase, although pH conditions should be considered to detect the catalytic activity of lipases, which are applicable to more acidic or alkaline pH circumstances. To validate the optimized conditions, the high-throughput screening of lipase activity was conducted using 17 domestic agricultural products. A pileus of Pleurotus eryngii showed the highest activity in both the spectrophotometric (633.42 μU/mg) and fluorometric (101.77 μU/mg) assays. The results of this research provide practical information for the high-throughput screening of lipases using alternative substrates on microplates.

Propeptide in Rhizopus chinensis Lipase: New Insights into Its Mechanism of Activity and Substrate Selectivity by Computational Design

Most fungal lipases contain a propeptide, which is very important for their function and substrate selectivity. In the present study, Rhizopus chinensis lipase (RCL) was used as a research model to explore the mechanism of the propeptide of the lipase. Conventional molecular dynamics (MD) and metadynamics simulations were used to explore the mechanism by which the propeptide affects the activity of the lipase, which was subsequently verified by mutation experiments. MD simulations indicated that the propeptide had an inhibitory effect on the lid movement of RCL and found a key region (Val5-Thr10) on the propeptide. Subsequently, site-directed mutations were created in this region. The mutations enhanced the lipase catalytic efficiency to 700% and showed the potential for the propeptide to shift the substrate specificity of RCL. The specificity and activity of RCL mutants also had similar trends to wild-type RCL toward triglycerides with varying chain lengths. The mutual corroboration of simulation and site-directed mutagenesis results revealed the vital role of the key propeptide region in the catalytic activity and substrate specificity of the lipase.

Sequence and structure-based method to predict diacylglycerol lipases in protein sequence

Lipase enzymes play a central role in biotechnology and the food industry. Diacylglyceride lipases (DAG) have received considerable attention due to their physiological significance and potential industrial usage. However, compared to the wide application of triacylglycerol (TAG) lipases, DAG lipases have a limited application due to their low thermostability and specific activity. The molecular basis of substrate specificity of DAG lipases remains elusive, making structure-guided engineering of TAG to DAG lipase difficult. Besides, the number of available DAG lipases is limited compared to TAG lipases. In the current study, we identified structural consensus motifs of DAG lipases that contribute to their DAG specificity on a structural comparison of DAG and TAG lipases. To find potential DAG lipases, sequence motifs and predicted secondary structures were used to screen millions of protein sequences and predict new DAG lipases. In total, 83 new putative DAG lipases were identified. The predicted DAG lipases were validated by expression of randomly chosen putative DAG lipases followed by functional assay for their DAG and TAG specific activity. The reported method is efficient and cost-effective for discovering new DAG lipases used in the food industry after the required characterization to meet potential application needs.

Cold Active Lipases: Biocatalytic Tools for Greener Technology

Lipases are enzymes that catalyze the ester bond hydrolysis in triglycerides with the release of fatty acids, mono- and diglycerides, and glycerol. The microbial lipases account for $400 million market size in 2017 and it is expected to reach $590 million by 2023. Many biotechnological processes are expedited at high temperatures and hence much research is dealt with thermostable enzymes. Cold active lipases are now gaining importance in the detergent, synthesis of chiral intermediates and frail/fragile compounds, and food and pharmaceutical industries. In addition, they consume less energy since they are active at low temperatures. These cold active lipases have not been commercially exploited so far compared to mesophilic and thermophilc lipases. Cold active lipases are distributed in microbes found at low temperatures. Only a few microbes were studied for the production of these enzymes. These cold-adapted enzymes show increased flexibility of their structures in response to freezing effect of the cold habitats. This review presents an update on cold-active lipases from microbial sources along with some structural features justifying high enzyme activity at low temperature. In addition, recent achievements on their use in various industries will also be discussed.

Identification, Classification, and Expression Analysis of the Triacylglycerol Lipase (TGL) Gene Family Related to Abiotic Stresses in Tomato

Triacylglycerol Lipases (TGLs) are the major enzymes involved in triacylglycerol catabolism. TGLs hydrolyze long-chain fatty acid triglycerides, which are involved in plant development and abiotic stress responses. Whereas most studies of TGLs have focused on seed oil metabolism and biofuel in plants, limited information is available regarding the genome-wide identification and characterization of the TGL gene family in tomato (Solanum lycopersicum L.). Based on the latest published tomato genome annotation ITAG4.0, 129 SlTGL genes were identified and classified into 5 categories according to their structural characteristics. Most SlTGL genes were distributed on 3 of 12 chromosomes. Segment duplication appeared to be the driving force underlying expansion of the TGL gene family in tomato. The promoter analysis revealed that the promoters of SlTGLs contained many stress responsiveness cis-elements, such as ARE, LTR, MBS, WRE3, and WUN-motifs. Expression of the majority of SlTGL genes was suppressed following exposure to chilling and heat, while it was induced under drought stress, such as SlTGLa9, SlTGLa6, SlTGLa25, SlTGLa26, and SlTGLa13. These results provide valuable insights into the roles of the SlTGL genes family and lay a foundation for further functional studies on the linkage between triacylglycerol catabolism and abiotic stress responses in tomato.

Directed evolution of Aspergillus oryzae lipase for the efficient resolution of (R,S)-ethyl-2-(4-hydroxyphenoxy) propanoate

Aspergillus oryzae lipase (AOL) is a potential biocatalyst for industrial application. In this study, a mutant lipase AOL-3^F38N/V230R was screened through two rounds of directed evolution, resulting in a fourfold increase in lipase activity, and threefold in catalytic efficiency (k_cat/K_m), while maintaining its excellent stereoselectivity. AOL-3^F38N/V230R enzyme activity was maximum at pH 7.5 and also at 40 °C. And compared with wild-type AOL-3, AOL-3^F38N/V230R preferentially hydrolyzed the fatty acid ethyl ester carbon chain length from C4 to C6-C10. In the same catalytic reaction conditions, the conversion of (R,S)-ethyl-2-(4-hydroxyphenoxy) propanoate ((R,S)-EHPP) by AOL-3^F38N/V230R can be increased 169.7% compared to the original enzyme. The e.e._s of (R,S)-EHPP achieved 99.4% and conversion about 50.2% with E value being 829.0. Therefore, AOL-3^F38N/V230R was a potential biocatalyst for obtaining key chiral compounds for aryloxyphenoxy propionate (APP) herbicides.

Biocatalysis at Extreme Temperatures: Enantioselective Synthesis of both Enantiomers of Mandelic Acid by Transesterification Catalyzed by a Thermophilic Lipase in Ionic Liquids at 120 °C

The use of biocatalysts in organic chemistry for catalyzing chemo-, regio- and stereoselective transformations has become an usual tool in the last years, both at lab and industrial scale. This is not only because of their exquisite precision, but also due to the inherent increase in the process sustainability. Nevertheless, most of the interesting industrial reactions involve water-insoluble substrates, so the use of (generally not green) organic solvents is generally required. Although lipases are capable of maintaining their catalytic precision working in those solvents, reactions are usually very slow and consequently not very appropriate for industrial purposes. Increasing reaction temperature would accelerate the reaction rate, but this should require the use of lipases from thermophiles, which tend to be more enantioselective at lower temperatures, as they are more rigid than those from mesophiles. Therefore, the ideal scenario would require a thermophilic lipase capable of retaining high enantioselectivity at high temperatures. In this paper, we describe the use of lipase from Geobacillus thermocatenolatus as catalyst in the ethanolysis of racemic 2-(butyryloxy)-2-phenylacetic to furnish both enantiomers of mandelic acid, an useful intermediate in the synthesis of many drugs and active products. The catalytic performance at high temperature in a conventional organic solvent (isooctane) and four imidazolium-based ionic liquids was assessed. The best results were obtained using 1-ethyl-3-methyl imidazolium tetrafluoroborate (EMIMBF4) and 1-ethyl-3-methyl imidazolium hexafluorophosphate (EMIMPF6) at temperatures as high as 120 °C, observing in both cases very fast and enantioselective kinetic resolutions, respectively leading exclusively to the (S) or to the (R)-enantiomer of mandelic acid, depending on the anion component of the ionic liquid.

Main Structural Targets for Engineering Lipase Substrate Specificity

Microbial lipases represent one of the most important groups of biotechnological biocatalysts. However, the high-level production of lipases requires an understanding of the molecular mechanisms of gene expression, folding, and secretion processes. Stable, selective, and productive lipase is essential for modern chemical industries, as most lipases cannot work in different process conditions. However, the screening and isolation of a new lipase with desired and specific properties would be time consuming, and costly, so researchers typically modify an available lipase with a certain potential for minimizing cost. Improving enzyme properties is associated with altering the enzymatic structure by changing one or several amino acids in the protein sequence. This review detailed the main sources, classification, structural properties, and mutagenic approaches, such as rational design (site direct mutagenesis, iterative saturation mutagenesis) and direct evolution (error prone PCR, DNA shuffling), for achieving modification goals. Here, both techniques were reviewed, with different results for lipase engineering, with a particular focus on improving or changing lipase specificity. Changing the amino acid sequences of the binding pocket or lid region of the lipase led to remarkable enzyme substrate specificity and enantioselectivity improvement. Site-directed mutagenesis is one of the appropriate methods to alter the enzyme sequence, as compared to random mutagenesis, such as error-prone PCR. This contribution has summarized and evaluated several experimental studies on modifying the substrate specificity of lipases.

Characterization and synthetic biology of lipase from Bacillus amyloliquefaciens strain

Lipases with high tolerance to temperature play a significant role in industry from food manufacturing to waste management systems. Thus, there is a need to investigate these enzymes from different geographical areas to look out for a more thermo-stable one. Characterization of lipases through experimental approaches is time consuming process and sometimes the results are ambiguous due to errors. However, integration of computational technologies is quite useful for prediction of optimized conditions. Such technologies can be applied as synthetic biology, which has many major applications in engineered biological approaches for accurate prediction of effects of different physical and chemical parameters on the system. In this study, cloning and expression of a lipase gene from Bacillus amyloliquefaciens, isolated from a novel geographical region of Pakistan, in Escherichia coli DH5α cells followed by sequencing was carried out. To isolate thermostable lipase producing strains, all the samples were kept at 50 °C. Genomic DNA was isolated and signal peptide (1-32 residues) sequence was chopped (ΔSPLipase). The ΔSPLipase was amplified and expressed in Linearized p15TV-L vector. The purified lipase appeared as single band of approximately 26 kDa. Suitable conditions of factors required for maximum lipase activity such as temperature, pH, substrate, organic solvent, detergents and metal ions were predicted through synthetic biology approach and further confirmed in wet lab. The predicted suitable factors for enzyme were almost similar to those determined experimentally. The optimum enzyme activity was recorded at pH 8 and 50 °C temperature. Interestingly, the activity of enzyme was found on a number of solvents, metal ions, detergents, and surfactants. The predicted optimum values and their experimental confirmations highlights the importance of integrated synthetic biology approaches in wet lab experiments. The characterized lipase of B. amyloliquefaciens at molecular level from Pakistani strains displayed good activity on a range of factors that implies this strain to be used for application in industrial level production.

Deletion and Randomization of Structurally Variable Regions in B. subtilis Lipase A (BSLA) Alter Its Stability and Hydrolytic Performance Against Long Chain Fatty Acid Esters

The continuous search for novel enzyme backbones and the engineering of already well studied enzymes for biotechnological applications has become an increasing challenge, especially by the increasing potential diversity space provided by directed enzyme evolution approaches and the demands of experimental data generated by rational design of enzymes. In this work, we propose a semi-rational mutational strategy focused on introducing diversity in structurally variable regions in enzymes. The identified sequences are subjected to a progressive deletion of two amino acids and the joining residues are subjected to saturation mutagenesis using NNK degenerate codons. This strategy offers a novel library diversity approach while simultaneously decreasing enzyme size in the variable regions. In this way, we intend to identify and reduce variable regions found in enzymes, probably resulting from neutral drift evolution, and simultaneously studying the functional effect of said regions. This strategy was applied to Bacillus. subtilis lipase A (BSLA), by selecting and deleting six variable enzyme regions (named regions 1 to 6) by the deletion of two amino acids and additionally randomizing the joining amino acid residues. After screening, no active variants were found in libraries 1% and 4%, 15% active variants were found in libraries 2% and 3%, and 25% for libraries 5 and 6 (n = 3000 per library, activity detected using tributyrin agar plates). Active variants were assessed for activity in microtiter plate assay (pNP-butyrate), thermal stability, substrate preference (pNP-butyrate, -palmitate), and compared to wildtype BSLA. From these analyses, variant P5F3 (F41L-ΔW42-ΔD43-K44P), from library 3 was identified, showing increased activity towards longer chain p-nitrophenyl fatty acid esters, when compared to BSLA. This study allowed to propose the targeted region 3 (positions 40-46) as a potential modulator for substrate specificity (fatty acid chain length) in BSLA, which can be further studied to increase its substrate spectrum and selectivity. Additionally, this variant showed a decreased thermal resistance but interestingly, higher isopropanol and Triton X-100 resistance. This deletion-randomization strategy could help to expand and explore sequence diversity, even in already well studied and characterized enzyme backbones such as BSLA. In addition, this strategy can contribute to investigate and identify important non-conserved regions in classic and novel enzymes, as well as generating novel biocatalysts with increased performance in specific processes, such as enzyme immobilization.

Rational Engineered C-Acyltransferase Transforms Sterically Demanding Acyl Donors

The biocatalytic Friedel-Crafts acylation has been identified recently for the acetylation of resorcinol using activated acetic acid esters for the synthesis of acetophenone derivatives catalyzed by an acyltransferase. Because the wild-type enzyme is limited to acetic and propionic derivatives as the substrate, variants were designed to extend the substrate scope of this enzyme. By rational protein engineering, the key residue in the active site was identified which can be replaced to allow binding of bulkier acyl moieties. The single-point variant F148V enabled the transformation of previously inaccessible medium chain length alkyl and alkoxyalkyl carboxylic esters as donor substrates with up to 99% conversion and up to >99% isolated yield.

Insight into Improved Thermostability of Cold-Adapted Staphylococcal Lipase by Glycine to Cysteine Mutation

Thermostability remains one of the most desirable traits in many lipases. Numerous studies have revealed promising strategies to improve thermostability and random mutagenesis often leads to unexpected yet interesting findings in engineering stability. Previously, the thermostability of C-terminal truncated cold-adapted lipase from Staphylococcus epidermidis AT2 (rT-M386) was markedly enhanced by directed evolution. The newly evolved mutant, G210C, demonstrated an optimal temperature shift from 25 to 45 °C and stability up to 50 °C. Interestingly, a cysteine residue was randomly introduced on the loop connecting the two lids and accounted for the only cysteine found in the lipase. We further investigated the structural and mechanistic insights that could possibly cause the significant temperature shift. Both rT-M386 and G210C were modeled and simulated at 25 °C and 50 °C. The results clearly portrayed the effect of cysteine substitution primarily on the lid stability. Comparative molecular dynamics simulation analysis revealed that G210C exhibited greater stability than the wild-type at high temperature simulation. The compactness of the G210C lipase structure increased at 50 °C and resulted in enhanced rigidity hence stability. This observation is supported by the improved and stronger non-covalent interactions formed in the protein structure. Our findings suggest that the introduction of a single cysteine residue at the lid region of cold-adapted lipase may result in unexpected increased in thermostability, thus this approach could serve as one of the thermostabilization strategies in engineering lipase stability.

Effects of Lid 1 Mutagenesis on Lid Displacement, Catalytic Performances and Thermostability of Cold-active Pseudomonas AMS8 Lipase in Toluene

Pseudomonas fluorescens AMS8 lipase lid 1 structure is rigid and holds unclear roles due to the absence of solvent-interactions. Lid 1 region was stabilized by 17 hydrogen bond linkages and displayed lower mean hydrophobicity (0.596) compared to MIS38 lipase. Mutating lid 1 residues, Thr-52 and Gly-55 to aromatic hydrophobic-polar tyrosine would churned more side-chain interactions between lid 1 and water or toluene. This study revealed that T52Y leads G55Y and its recombinant towards achieving higher solvent-accessible surface area and longer half-life at 25 to 37 °C in 0.5% (v/v) toluene. T52Y also exhibited better substrate affinity with long-chain carbon substrate in aqueous media. The affinity for pNP palmitate, laurate and caprylate increased in 0.5% (v/v) toluene in recombinant AMS8, but the affinity in similar substrates was substantially declined in lid 1 mutated lipases. Regarding enzyme efficiency, the recombinant AMS8 lipase displayed highest value of k_cat/K_m in 0.5% (v/v) toluene, mainly with pNPC. In both hydrolysis reactions with 0% and 0.5% (v/v) toluene, the enzyme efficiency of G55Y was found higher than T52Y for pNPL and pNPP. At 0.5% (v/v) toluene, both mutants showed reductions in activation energy and enthalpy values as temperature increased from 25 to 35 °C, displaying better catalytic functions. Only T52Y exhibited increase in entropy values at 0.5% (v/v) toluene indicating structure stability. As a conclusion, Thr-52 and Gly-55 are important residues for lid 1 stability as their existence helps to retain the geometrical structure of alpha-helix and connecting hinge.

N-terminal domain replacement changes an archaeal monoacylglycerol lipase into a triacylglycerol lipase

BACKGROUND

Lipolytic enzymes of hyperthermophilic archaea generally prefer small carbon chain fatty acid esters (C₂-C₁₂) and are categorized as esterases. However, a few have shown activity with long-chain fatty acid esters, but none of them have been classified as a true lipase except a lipolytic enzyme AFL from Archaeglobus fulgidus. Thus, our main objective is to engineer an archaeal esterase into a true thermostable lipase for industrial applications. Lipases which hydrolyze long-chain fatty acid esters display an interfacial activation mediated by the lid domain which lies over active site and switches to open conformation at the oil-water interface. Lid domains modulate enzyme activities, substrate specificities, and stabilities which have been shown by protein engineering and mutational analyses. Here, we report engineering of an uncharacterized monoacylglycerol lipase (TON-LPL) from an archaeon Thermococcus onnurineus (strain NA1) into a triacylglycerol lipase (rc-TGL) by replacing its 61 N-terminus amino acid residues with 118 residues carrying lid domain of a thermophilic fungal lipase-Thermomyces lanuginosus (TLIP).

RESULTS

TON-LPL and rc-TGL were cloned and overexpressed in E. coli, and the proteins were purified by Ni-NTA affinity chromatography for biochemical studies. Both enzymes were capable of hydrolyzing various monoglycerides and shared the same optimum pH of 7.0. However, rc-TGL showed a significant decrease of 10 °C in its optimum temperature (T_opt). The far UV-CD spectrums were consistent with a well-folded α/β-hydrolase fold for both proteins, but gel filtration chromatography revealed a change in quaternary structure from trimer (TON-LPL) to monomer (rc-TGL). Seemingly, the difference in the oligomeric state of rc-TGL may be linked to a decrease in temperature optimum. Nonetheless, rc-TGL hydrolyzed triglycerides and castor oil, while TON-LPL was not active with these substrates.

CONCLUSIONS

Here, we have confirmed the predicted esterase activity of TON-LPL and also performed the lid engineering on TON-LPL which effectively expanded its substrate specificity from monoglycerides to triglycerides. This approach provides a way to engineer other hyperthermophilic esterases into industrially suitable lipases by employing N-terminal domain replacement. The immobilized preparation of rc-TGL has shown significant activity with castor oil and has a potential application in castor oil biorefinery to obtain value-added chemicals.

Lipase-catalyzed selective enrichment of omega-3 polyunsaturated fatty acids in acylglycerols of cod liver and linseed oils: Modeling the binding affinity of lipases and fatty acids

Present study employed molecular modeling method to elucidate the binding affinity of lipases with fatty acids of different chain lengths; and investigated the effects of lipases positional and fatty acids specificity on omega-3 polyunsaturated fatty acids (ω-3 PUFAs) enrichment in cod liver and linseed oils. Among the lipases studied, molecular modeling showed the active sites of Candida rugosa lipase (CRL) had a low C-Docker interactive energy for saturated (SFA) and monounsaturated (MUFA) fatty acids which predicted CRL to have highest preferences to selectively hydrolyze resulting in efficient enrichment of ω-3 PUFAs. Verification experiments showed the SFA and MUFA in the acylglycerol fraction includes monoacylglcyerols (MAG), diacyglycerols (DAG), and triacylglycerols (TAG) of CRL-hydrolyzed cod liver oil decreased from the initial 25.21 to 16.88% and 45.25 to 32.17%, respectively. In addition, CRL-hydrolyzed cod liver oil demonstrated 88.36% of ω-3 PUFAs enrichment. The regio-distribution of fatty acids in CRL-hydrolyzed cod liver oil were not significantly different than that of cod liver oil indicating the ω-3 PUFAs enrichment was due to fatty acids selectivity and not positional selectivity of CRL.

Comparison of Candida antarctica Lipase B Variants for Conversion of ε-Caprolactone in Aqueous Medium-Part 2

Enzyme-catalyzed ring-opening polymerization of lactones is a method of increasing interest for the synthesis of polyesters. In the present work, we investigated which changes in the structure of Candida antarctica lipase B (CaLB) shift the catalytic equilibrium between esterification and hydrolysis towards polymerization. Therefore, we present two concepts: (i) removing the glycosylation of CaLB to increase the surface hydrophobicity; and (ii) introducing a hydrophobic lid adapted from Pseudomonas cepacia lipase (PsCL) to enhance the interaction of a growing polymer chain to the elongated lid helix. The deglycosylated CaLB (CaLB-degl) was successfully generated by site-saturation mutagenesis of asparagine 74. Furthermore, computational modeling showed that the introduction of a lid helix at position Ala148 was structurally feasible and the geometry of the active site remained intact. Via overlap extension PCR the lid was successfully inserted, and the variant was produced in large scale in Pichia pastoris with glycosylation (CaLB-lid) and without (CaLB-degl-lid). While the lid variants show a minor positive effect on the polymerization activity, CaLB-degl showed a clearly reduced hydrolytic and enhanced polymerization activity. Immobilization in a hydrophobic polyglycidol-based microgel intensified this effect such that a higher polymerization activity was achieved, compared to the "gold standard" Novozym® 435.

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.

Impact of signal peptide and transmembrane segments on expression and biochemical properties of a lipase from Bacillus sphaericus 205y

A total of 97 amino acids, considered as the signal peptide and transmembrane segments were removed from 205y lipase gene using polymerase chain reaction technique that abolished the low activity of this enzyme. The mature enzyme was expressed in Escherichia coli using pBAD expression vector, which gave up to a 13-fold increase in lipase activity. The mature 205y lipase (without signal peptide and transmembrane; -SP/TM) was purified to homogeneity using the isoelectric focusing technique with 53% recovery. Removing of the signal peptide and transmembrane segments had resulted in the shift of optimal pH, an increase in optimal temperature and tolerance towards more water-miscible organic solvents as compared to the characteristics of open reading frame (ORF) of 205y lipase. Also, in the presence of 1mM inhibitors, less decrease in the activity of mature 205y lipase was observed compared to the ORF of the enzyme. Protein structure modeling showed that 205y lipase consisted of an α/β hydrolase fold without lid domain. However, the transmembrane segment could effect on the enzyme activity by covering the active site or aggregation the protein.

Characterization of a Novel Alkalophilic Lipase From Aneurinibacillus thermoaerophilus: Lid Heterogeneity and Assignment to Family I.5

Recent investigations of Aneurinibacillus thermoaerophilus strains have allowed identification of a unique solvent tolerant lipase, distinct from known lipases. This work reports the expression and purification of this lipase (LipAT) and the first characterization of its structure and temperature and pH-dependent behaviour. LipAT has a secondary structural content compatible with the canonical lipase α/β hydrolase fold, and is dimeric at neutral pH. The protein was folded from pH 5 to 10, and association into folded aggregates at pH 7 and 8 likely protected its secondary structures from thermal unfolding. The enzyme was active from 25 to 65 °C under neutral pH, but its maximal activity was detected at pH 10 and 45 °C. The ability of LipAT to recover from high temperature was investigated. Heating at 70 °C and pH 10 followed by cooling prevented the restoration of activity, while similar treatments performed at pH 8 (where folded aggregates may form) allowed recovery of 50% of the initial activity. In silico analyses revealed a high conservation (85% or more) for the main lipase signature sequences in LipAT despite an overall low residue identity (60% identity compared to family I.5 lipases). In contrast, the active site lid region in LipAT is very distinct showing only 25% amino acid sequence identity to other homologous lipases in this region. Comparison of lids among lipases from the I.5 family members and LipAT reveals that this region should be a primary target for elucidation, optimisation and prediction of structure-function relationships in lipases.

Improved Performance of Magnetic Cross-Linked Lipase Aggregates by Interfacial Activation: A Robust and Magnetically Recyclable Biocatalyst for Transesterification of Jatropha Oil

Lipases are the most widely employed enzymes in commercial industries. The catalytic mechanism of most lipases involves a step called "interfacial activation". As interfacial activation can lead to a significant increase in catalytic activity, it is of profound importance in developing lipase immobilization methods. To obtain a potential biocatalyst for industrial biodiesel production, an effective strategy for enhancement of catalytic activity and stability of immobilized lipase was developed. This was performed through the combination of interfacial activation with hybrid magnetic cross-linked lipase aggregates. This biocatalyst was investigated for the immobilization of lipase from Rhizomucor miehei (RML). Under the optimal conditions, the activity recovery of the surfactant-activated magnetic RML cross-linked enzyme aggregates (CLEAs) was as high as 2058%, with a 20-fold improvement over the free RML. Moreover, the immobilized RML showed excellent catalytic performance for the biodiesel reaction at a yield of 93%, and more importantly, could be easily separated from the reaction mixture by simple magnetic decantation, and retained more than 84% of its initial activities after five instances of reuse. This study provides a new and versatile approach for designing and fabricating immobilized lipase with high activation and stability.

New member of the hormone-sensitive lipase family from the permafrost microbial community

Siberian permafrost is a unique environment inhabited with diverse groups of microorganisms. Among them, there are numerous producers of biotechnologically relevant enzymes including lipases and esterases. Recently, we have constructed a metagenomic library from a permafrost sample and identified in it several genes coding for potential lipolytic enzymes. In the current work, properties of the recombinant esterases obtained from this library are compared with the previously characterized lipase from Psychrobacter cryohalolentis and other representatives of the hormone-sensitive lipase family.

Liquid lipases for enzymatic concentration of n-3 polyunsaturated fatty acids in monoacylglycerols via ethanolysis: Catalytic specificity and parameterization

This work examined catalytic specificity and fatty acid selectivity of five liquid lipases C. antarctica lipase A and B (CAL-A/B), and lipase TL (T. lanuginosus), Eversa Transfrom and NS in ethanolysis of fish oil with the aim to concentrate n-3 PUFAs into monoacylglycerols (MAGs) products. Lipase TL, Eversa Transform & NS entail a much faster reaction and produce higher MAGs yield (>30%); whereas CAL-A obtains the highest concentration of n-3 PUFAs/DHA/EPA into MAGs products (88.30%); followed by lipase NS (81.02%). ¹³C NMR analysis indicates that CAL-B and lipase TL are sn-1,3 specific; but CAL-A and lipase Eversa Transform are non-regiospecific or weak sn-2 specific; which plausibly explains high enrichment effect of the latter two lipases. All liquid lipases are observed reusable for a certain times (lipase Eversa Transform up to 12 times), demonstrating their competitive advantage over immobilized form for industrial application because of their higher activity and cheaper operation cost.

The near-ideal catalytic property of Candida antarctica lipase A to highly concentrate n-3 polyunsaturated fatty acids in monoacylglycerols via one-step ethanolysis of triacylglycerols

Declining quantity/quality of available n-3 polyunsaturated fatty acids (n-3 PUFAs) resources demand innovative technology to concentrate n-3 PUFAs from low quality oils into value-added products/health-beneficial ingredients rich in n-3 PUFAs. This work proposed the catalytic property and specificity of an ideal enzyme required to tackle this task and identified Candida antarctica lipase A (CAL-A) is such a near-ideal enzyme in practice, which concentrates n-3 PUFAs from 25% to 27% in oils to a theoretically closer value 90% in monoacylglycerols (MAGs) via one-step enzymatic ethanolysis. Non-regiospecificity and high non-n-3 PUFAs preference of CAL-A are the catalytic feature to selectively cleave non-n-3 PUFAs in all 3 positions of triacylglycerols (TAGs); while high ethanol/TAGs ratio, low operation temperature and high tolerance to polar ethanol are essential conditions beyond biocatalyst itself. C-13 Nuclear magnetic resonance ((13)C NMR) analysis and competitive factor estimation verified the hypothesis and confirmed the plausible suggestion of catalytic mechanism of CAL-A.

SECRETION OF LIPASES IN THE DIGESTIVE TRACT OF THE CRICKET Gryllus bimaculatus

Little is known concerning the sites and the ratios of the lipase secretions in insects, therefore we undertook an examination of the lipase secretion of fed and unfed adult female Gryllus bimaculatus. The ratio of triacylglyceride lipase, diacylglyceride lipase, and phosphatidylcholine lipase secreted by fed females in the caecum and ventriculus is 1:1.4:0.4. These activities decrease in the caecum by 30-40% in unfed females. The total lipase activity (TLA) in the caecum is about 10 times that in the ventriculus. Minimal lipase secretion occurs before and during the final moult, and remains at this level in unfed crickets, indicating a basal secretion rate. In 2-day-old fed females, about 10% of the TLA in the entire gut is found in the crop, about 70% in the caecum, 20% in the ventriculus, and 3% in the ileum. Lipases in the ventriculus are recycled back to the caecum and little is lost in the feces. Oleic acid stimulated in vitro lipase secretion, but lipids did not. Feeding stimulated lipase secretion, starvation reduced lipase secretion, but this does not prove a direct prandal regulation of secretion, because feeding also induced a size and volume increase of the caecum.