Solvent Screening, Optimization and Kinetic Parameters of The Biocatalytic Epoxidation Reaction of Beta-Pinene Mediated by Novozym®435

Monoterpenes are secondary metabolites widely used in the flavors and fragrance industries and can have their structure altered to enhance their applicability, such as producing epoxides, which are used as synthetic blocks for pharmaceuticals. Epoxides are commonly synthesized by the use of inorganic acids as catalysts, although the acid medium induces epoxide degradation. To overcome these limitations biocatalysis is shown as an alternative, in view that lipases can perform the reaction in a non-acidic medium. Related to, this work aimed to perform the synthesis of beta-Pinene epoxide using Pseudozyma antarctica lipase B (Novozym®435) as biocatalyst and to determine the independent variables that influence the reaction using experimental design tools. Different solvent systems were evaluated for until 72 h, in reactions with molar ratio of 2:2:1 (beta-Pinene, octanoic acid, and urea-hydrogen peroxide - UHP) at 40°C, 250 rpm, and 10%(w/v) of the biocatalyst. Ethyl acetate showed higher conversion (40% in 24 h) into the product without the formation of by-products. The atom economy (AE) was determined using metrics of green chemistry and ethyl acetate proved to have a higher atom economy (67.8%), while the other solvents that used octanoic acid as an acyl donor had 41.3%. In the following reactions, ethyl acetate was maintained as the solvent, while the temperature, molar ratio, and the percentage of the biocatalyst were varied. The increase in the molar ratio (beta-Pinene:UHP, 1:1) and percentage of biocatalyst (20%w/v) resulted in 80% of the product after 3 hof reaction at 40°C. To evaluate the impact of each independent variable, an FFD was performed by varying temperature, molar ratio, stirring, and percentage of enzyme, in one level. All variables were statistically significant, with different rates of impact. Due to this, the same variables were maintained on the CCRD, varying in two levels. The conversion ranged from good to excellent (32 - 93%). The independent variables that influenced the direction were temperature > stirring > molar ratio. In conclusion, the combination of two different tools of experimental design provided the development of an optimized model for beta-Pinene epoxidation, achieving high yields within 3 h.

Characterization of a Pentacyclic Triterpene Acetyltransferase Involved in the Biosynthesis of Taraxasterol and ψ-Taraxasterol Acetates in Lettuce

Triterpenoids exist in a free state and/or in conjugated states, such as triterpene glycosides (saponins) or triterpene esters. There is no information on the enzyme participating in the production of triterpene esters from free triterpenes. Lettuce (Lactuca sativa) contains various pentacyclic triterpene acetates (taraxasterol acetates, ψ-taraxasterol acetates, taraxerol acetates, lupeol acetates, α-amyrin acetates, β-amyrin acetates, and germanicol acetate). In this study, we report a novel triterpene acetyltransferase (LsTAT1) in lettuce involved in the biosynthesis of pentacyclic triterpene acetates from free triterpenes. The deduced amino acid sequences of LsTAT1 showed a phylogenetic relationship (43% identity) with those of sterol O-acyltransferase (AtSAT1) of Arabidopsis thaliana and had catalytic amino acid residues (Asn and His) that are typically conserved in membrane-bound O-acyltransferase (MBOAT) family proteins. An analysis of LsTAT1 enzyme activity in a cell-free system revealed that the enzyme exhibited activity for the acetylation of taraxasterol, ψ-taraxasterol, β-amyrin, α-amyrin, lupeol, and taraxerol using acetyl-CoA as an acyl donor but no activity for triterpene acylation using a fatty acyl donor. Lettuce oxidosqualene cyclase (LsOSC1) is a triterpene synthase that produces ψ-taraxasterol, taraxasterol, β-amyrin and α-amyrin. The ectopic expression of both the LsOSC1 and LsTAT1 genes in yeast and tobacco could produce taraxasterol acetate, ψ-taraxasterol acetate, β-amyrin acetate, and α-amyrin acetate. However, expression of the LsTAT1 gene in tobacco was unable to induce the conversion of intrinsic sterols (campesterol, stigmasterol, and β-sitosterol) to sterol acetates. The results demonstrate that the LsTAT1 enzyme is a new class of acetyltransferase belong to the MBOAT family that have a particular role in the acetylation of pentacyclic triterpenes and are thus functionally different from sterol acyltransferase conjugating fatty acyl esters.

Employing lipase of candida antarctica (calb) as catalyst in the acetylation of para-aminophenol in aqueous and water-free medium

Candida antarctica lipase B (CaLB) is one of lipase classes enzymes that has many advantages to be used in the process of synthesizing organic compounds. In this study, some experiments were conducted to examine the ability of CaLB as a catalyst in the para-aminophenol (PAP) acetylation to produce paracetamol as the result. Two types of research have been carried out, the first one is to utilize CaLB to catalyze acetylation of PAP in a water-free reaction medium, and the second one is to use CaLB as catalyst in aqueous medium through oxidative amidation reaction. Reaction in water free system was held in ethyl catalyst acetate as solvent that also act as the acyl donor, while in the aqueous medium, acetylacetone was used as acyl donor and ethyl acetate as source to produce peracid that will be used as oxidator. Analysis was done by HPLC and TLC densitometric to follow the amount of paracetamol produced. The results of CaLB-catalyzed acylation in water free system showed that the enzyme could accept PAF and ethyl acetate as a substrate in a nucleophilic substitution reaction, resulting in paracetamol as a product. However, the yield from the acylation of PAP is still not satisfactory. In the reaction in aqueous medium, CaLB has been proven to show its activity to catalyze the acylation of PAP with acetylacetone, as well as the reaction of peracid formation from ethyl acetate. The results show that this strategy can work well and give better yields than the other reaction in water-free medium.

The structural basis for the phospholipid remodeling by lysophosphatidylcholine acyltransferase 3

As the major component of cell membranes, phosphatidylcholine (PC) is synthesized de novo in the Kennedy pathway and then undergoes extensive deacylation-reacylation remodeling via Lands’ cycle. The re-acylation is catalyzed by lysophosphatidylcholine acyltransferase (LPCAT) and among the four LPCAT members in human, the LPCAT3 preferentially introduces polyunsaturated acyl onto the sn-2 position of lysophosphatidylcholine, thereby modulating the membrane fluidity and membrane protein functions therein. Combining the x-ray crystallography and the cryo-electron microscopy, we determined the structures of LPCAT3 in apo-, acyl donor-bound, and acyl receptor-bound states. A reaction chamber was revealed in the LPCAT3 structure where the lysophosphatidylcholine and arachidonoyl-CoA were positioned in two tunnels connected near to the catalytic center. A side pocket was found expanding the tunnel for the arachidonoyl CoA and holding the main body of arachidonoyl. The structural and functional analysis provides the basis for the re-acylation of lysophosphatidylcholine and the substrate preference during the reactions.

Chemoenzymatic Stereoselective Synthesis of trans-Flavan-4-ols via Lipase-Catalyzed Kinetic Resolutions

Flavan-4-ols are a subclass of flavonoids that are present in complex molecules with application in the industrial sector as pigments, antioxidants, or antimitotics, among many others. The most traditional way to achieve their synthesis is from naturally abundant flavanones, asymmetric transfer hydrogenation reactions or bioreduction being well known strategies, while their preparation from racemic flavan-4-ols has been less explored. In this article, we have focused on the synthesis of a series of trans-flavan-4-ols bearing different substitution patterns in the aromatic ring to explore later the potential of lipases as biocatalysts for stereoselective acylation reactions. Therefore, a series of flavanones have been chemically prepared, starting from the corresponding benzaldehydes by aldol condensation with 2′-hydroxyacetophenone in a strongly basic medium, and later transformed into the corresponding racemic trans-flavan-4-ols following a carbonyl reduction, Mitsunobu reaction, and ester deprotection sequence. A screening of lipases and optimization of the reaction conditions for the stereoselective acylation of racemic 2-phenylchroman-4-ol were performed before expanding the best reaction conditions to the kinetic resolution of other 2-arylchroman-4-ols. Interestingly, the combination of AK lipase from Pseudomonas fluorescens as enzyme and vinyl acetate as both acyl donor and solvent allowed the performance of highly asymmetric transformations (E > 200, 50–90% eeS and >99% eeP) under mild reaction conditions (30 °C and 250 rpm).

Rational Design for Enhanced Acyltransferase Activity in Water Catalyzed by the Pyrobaculum calidifontis VA1 Esterase

Biocatalytic transesterification is commonly carried out employing lipases in anhydrous organic solvents since hydrolases usually prefer hydrolysis over acyl transfer in bulk water. However, some promiscuous acyltransferases can catalyze acylation in an aqueous solution. In this study, a rational design was performed to enhance the acyltransferase selectivity and substrate scope of the Pyrobaculum calidifontis VA1 esterase (PestE). PestE wild type and variants were applied for the acylation of monoterpene alcohols. The mutant PestE_I208A is selective for (–)-menthyl acetate (E-Value = 55). Highly active acyltransferases were designed, allowing for complete conversion of (–)-citronellol to citronellyl acetate. Additionally, carvacrol was acetylated but with lower conversions. To the best of our knowledge, this is the first example of the biocatalytic acylation of a phenolic alcohol in bulk water. In addition, a high citronellol conversion of 92% was achieved with the more environmentally friendly and inexpensive acyl donor ethyl acetate using PestE_N288F as a catalyst. PestE_N288F exhibits good acyl transfer activity in an aqueous medium and low hydrolysis activity at the same time. Thus, our study demonstrates an alternative synthetic strategy for acylation of compounds without organic solvents.

Genes Involved in Lipid Metabolism in Coconut

Coconut palm (Cocos nucifera L) is an economically important monocot plant grown in tropical and subtropical regions. Coconut oil is stored in a solid endosperm and has 47.48–50.5% fatty acid component as lauric acid (C12:0). Present research showed that acyl-acyl carrier protein thioesterases (FatA/B) and lysophosphatidic acid acyltransferase (LAAPT) are key enzymes determining medium-chain fatty acid accumulation in coconut oil. Among five CnFatB genes, CnFatB3 expressed specifically in endosperm and in vitro experiment showed that this gene made mainly lauric acid (C12:0) and tetradecenoic acid (C14:1). Overexpression of CnFatB3 in Arabidopsis increased the amounts of C12:0 and C14:0 in transgenic plant. CnLPAAT gene that is expressed specifically in coconut endosperm showed a preference for using acyl-CoAs containing C10:0, C12:0, and C14:0 acyl groups as acyl-donor substrates. Coconut and oil palm are closely related species with approximately 50% lauric acid (C12:0) in their endosperm. The two species have a close evolutionary relationship between predominant gene isoforms and high conservation of gene expression bias in the lipid metabolism pathways. Moreover, since no stable transformation system has been constructed in coconut palm, gene function validations have been done in vitro, or genes transformed into a heterologous system.

Biosynthesis of a Novel Antibacterial Dipeptide, Using Proteases From South American Native Fruits, Useful as a Food Preservative

Antiacanthain and granulosain are the partially purified proteolytic extracts from the South American native fruits of Bromelia antiacantha (Bertol. ) and Solanum granuloso leprosum, respectively. The aim of this work was to compare the ability of both soluble and immobilized antiacanthain and granulosain f or the synthesis of Z-Tyr-Val-OH, a novel antibacterial dipeptide, in different reaction systems formed by almost anhydrous organic solvents (Xw: 1 × 10−5) and several percentages of immiscible organic solvents in 100 mM Tris(hydroxymethyl)aminomethane hydrochloride buffer pH 8.0. Soluble antiacanthain in half of the 24 different organic biphasic media showed higher catalytic potential than in 100 mM Tris(hydroxymethyl)aminomethane hydrolchloride buffer pH 8.0. Soluble granulosain showed lower catalytic potential in all liquid-liquid biphasic media than in the same buffer. However, 50% (v/v) ethyl ethanoate in 100 mM Tris(hydroxymethyl)aminomethane hydrolchloride buffer pH 8.0 allowed to express the highest catalytic potential of both soluble enzymes. In 50% v/v ethyl ethanoate, soluble antiacanthain and granulosain catalyzed the synthesis of Z-Tyr-Val-OH with 72 ± 0.15 and 60 ± 0.10% maximal peptide yields, respectively. Multi-point immobilization in glyoxyl-silica did not lead to better peptide yields than soluble enzymes, in that liquid-liquid biphasic medium under the same reaction conditions. Soluble and glyoxyl-silica immobilized antiacanthain in almost anhydrous ethyl ethanoate (Xw: 1 × 10−5) were able to retain 17.3 and 45% of the initial proteolytic activity of antiacanthain in 100 mM Tris hydrolchloride buffer pH 8.0, respectively, at 40°C under agitation (200 rpm). Soluble and glyoxyl-silica immobilized granulosain were inactivated under the same reaction conditions. Glyoxyl-silica immobilized antiacanthain showed to be a robust biocatalyst in almost anhydrous ethyl ethanoate (Xw: 1 × 10−5), eliciting the best peptide yield (75 ± 0.13%). The synthesis reaction of Z-Tyr-Val-OH could not proceed when soluble antiacanthain was used under the same conditions. Both peptidases only catalyzed the synthesis reaction under kinetic control, using activated acyl donor substrates. Finally, this work reports a novel broad-spectrum antibacterial peptide that significantly decreased (p ≤ 0.05) the specific growth rates of Gram positive and Gram negative microorganisms at very low concentrations (≥15 and 35 μg/ml, respectively); contributing with a new safe food preservative of applying for different food systems.

Research Progress in Enzymatic Synthesis of Vitamin E Ester Derivatives

Vitamin E is easily oxidized by light, air, oxidizing agents and heat, limiting its application in many ways. Compared to vitamin E, vitamin E ester derivatives exhibit improved stability and a stronger antioxidant capacity, and even gain new biological functions. In recent years, enzymatic synthesis of vitamin E ester derivatives has received increasing attention due to its environmental friendliness, high catalytic efficiency, and inherent selectivity. This paper reviews the related progress of lipase-mediated preparation of vitamin E ester derivatives. The function of different vitamin E ester derivatives, and the main factors influencing the enzymatic acylation process, including enzyme species, acyl donor and acceptor, reaction media and water activity, are summarized in this paper. Finally, the perspective of lipase-catalyzed synthesis of vitamin E ester derivatives is also discussed.

Structural insights into acyl-ACP selective recognition by the Aeromonas hydrophila AHL synthase AhyI

Background Aeromonas hydrophila is a gram-negative bacterium and the major causative agent of the fish disease motile aeromonad septicemia (MAS). It uses N-acyl-homoserine lactone (AHL) quorum sensing signals to coordinate biofilm formation, motility, and virulence gene expression. The AHL signaling pathway is therefore considered to be a therapeutic target against pathogenic A. hydrophila infection. In A. hydrophila, AHL autoinducers biosynthesis are specifically catalyzed by an ACP-dependent AHL synthase AhyI using the precursors SAM and acyl-ACP. Our previously reported AhyI was heterologously expressed in E. coli, which showed the production characteristics of medium-long chain AHLs. This contradicted the prevailing understanding that AhyI was only a short-chain C4/C6-HSL synthase. Results In this study, six linear acyl-ACP proteins with C-terminal his-tags were synthesized in Vibrio harveyi AasS using fatty acids and E. coli produced active holo-ACP proteins, and in vitro biosynthetic assays of six AHL molecules and kinetic studies of recombinant AhyI with a panel of four linear acyl-ACPs were performed. UPLC-MS/MS analyses indicated that AhyI can synthesize short-, medium- and long-chain AHLs from SAM and corresponding linear acyl-ACP substrates. Kinetic parameters measured using a DCPIP colorimetric assay, showed that there was a notable decrease in catalytic efficiency with acyl-chain lengths above C6, and hyperbolic or sigmoidal responses in rate curves were observed for varying acyl-donor substrates. Primary sequence alignment of the six representative AHL synthases offers insights into the structural basis for their specific acyl substrate preference. To further understand the acyl chain length preference of AhyI for linear acyl-ACP, we performed a structural comparison of three ACP-dependent LuxI homologs (TofI, BmaI1 and AhyI) and identified three key hydrophobic residues (I67, F125 and L157) which confer AhyI to selectively recognize native C4/C6-ACP substrates. These predictions were further supported by a computational Ala mutation assay. Conclusions In this study, we have redefined AhyI as a multiple short- to long-chain AHL synthase which uses C4/C6-ACP as native acyl substrates and longer acyl-ACPs (C8 ~ C14) as non-native ones. We also theorized that the key residues in AhyI would likely drive acyl-ACP selective recognition.