Biosynthesis of ethyl caproate and other short ethyl esters catalyzed by cutinase in organic solvent

Cutinases: Characteristics and Insights in Industrial Production

Cutinases (EC 3.1.1.74) are serin esterases that belong to the α/β hydrolases superfamily and present in the Ser-His-Asp catalytic triad. They show characteristics between esterases and lipases. These enzymes hydrolyze esters and triacylglycerols and catalyze esterification and transesterification reactions. Cutinases are synthesize by plant pathogenic fungi, but some bacteria and plants have been found to produce cutinases as well. In nature they facilitate a pathogen’s invasion by hydrolyzing the cuticle that protects plants, but can be also used for saprophytic fungi as a way to nourish themselves. Cutinases can hydrolyze a wide range of substrates like esters, polyesters, triacylglycerols and waxes and that makes this enzyme very attractive for industrial purposes. This work discusses techniques of industrial interest such as immobilization and purification, as well as some of the most important uses of cutinases in industries.

Biotic and Abiotic Synthesis of Renewable Aliphatic Polyesters from Short Building Blocks Obtained from Biotechnology

Biobased polymers have seen their attractiveness increase in recent decades thanks to the significant development of biorefineries to allow access to a wide variety of biobased building blocks. Polyesters are one of the best examples of the development of biobased polymers because most of them now have their monomers produced from renewable resources and are biodegradable. Currently, these polyesters are mainly produced by using traditional chemical catalysts and harsh conditions, but recently greener pathways with nontoxic enzymes as biocatalysts and mild conditions have shown great potential. Bacterial polyesters, such as poly(hydroxyalkanoate)s (PHA), are the best example of the biotic production of high molar mass polymers. PHAs display a wide variety of macromolecular architectures, which allow a large range of applications. The present contribution aims to provide an overview of recent progress in studies on biobased polyesters, especially those made from short building blocks, synthesized through step-growth polymerization. In addition, some important technical aspects of their syntheses through biotic or abiotic pathways have been detailed.

Immobilization of a Cutinase from Fusarium oxysporum and Application in Pineapple Flavor Synthesis

In the present study, the immobilization of a cutinase from Fusarium oxysporum was carried out as cross-linked enzyme aggregates. Under optimal immobilization conditions, acetonitrile was selected as precipitant, utilizing 9.4 mg protein/mL and 10 mM glutaraldehyde as cross-linker. The immobilized cutinase (imFocut5a) was tested in isooctane for the synthesis of short-chain butyrate esters, displaying enhanced thermostability compared to the free enzyme. Pineapple flavor (butyl butyrate) synthesis was optimized, leading to a conversion yield of >99% after 6 h, with an initial reaction rate of 18.2 mmol/L/h. Optimal reaction conditions were found to be 50 °C, a vinyl butyrate/butanol molar ratio of 3:1, vinyl butyrate concentration of 100 mM, and enzyme loading of 11 U. Reusability studies of imFocut5a showed that after four consecutive runs, the reaction yield reaches 54% of the maximum. The efficient bioconversion offers a sustainable and environmentally friendly process for the production of "natural" aroma compounds essential for the food industry.

Characterization of an acidic cold-adapted cutinase from Thielavia terrestris and its application in flavor ester synthesis

An acidic cutinase (TtcutB) from Thielavia terrestris CAU709 was purified to apparent homogeneity with 983 Um g(-1) specific activity. The molecular mass of the enzyme was estimated to be 27.3 and 27.9 kDa by SDS-PAGE and gel filtration, respectively. A peptide sequence homology search revealed no homologous cutinases from T. terrestris, except for one putative cutinase gene (XP003656017.1), indicating that TtcutB is a novel enzyme. TtcutB exhibited an acidic pH optimum of 4.0, and stability at pH 2.5-10.5. Optimal activity was at 55 °C, it was stable up to 65 °C, and retained over 30% activity at 0 °C. Km values toward p-nitrophenyl (pNP) acetate, pNP-butyrate and pNP-caproate were 8.3, 1.1 and 0.88 mM, respectively. The cutinase exhibited strong synthetic activity on flavor ester butyl butyrate under non-aqueous environment, and the highest esterification efficiency of 95% was observed under the optimized reaction conditions. The enzyme's unique biochemical properties suggest great potential in flavor esters-producing industries.

Cloning and characterization of a novel acidic cutinase from Sirococcus conigenus

A cutinase gene (ScCut1) was amplified by PCR from the genomic DNA of the ascomycetous plant pathogen Sirococcous conigenus VTT D-04989 using degenerate primers designed on the basis of conserved segments of known cutinases and cutinase-like enzymes. No introns or N- or O-glycosylation sites could be detected by analysis of the ScCut1 gene sequence. The alignment of ScCut1 with other fungal cutinases indicated that ScCut1 contained the conserved motif G-Y-S-Q-G surrounding the active site serine as well as the aspartic acid and histidine residues of the cutinase active site. The gene was expressed in Pichia pastoris, and the recombinantly produced ScCut1 enzyme was purified to homogeneity by immobilized metal affinity chromatography exploiting a C-terminal His-tag translationally fused to the protein. The purified ScCut1 exhibited activity at acidic pH. The K(m) and V(max) values determined for pNP-butyrate esterase activity at pH 4.5 were 1.7 mM and 740 nkat mg⁻¹, respectively. Maximal activities were determined at between pH 4.7 and 5.2 and at between pH 4.1 and 4.6 with pNP-butyrate and tritiated cutin as the substrates, respectively. With both substrates, the enzyme was active over a broad pH range (between pH 3.0 and 7.5). Activity could still be detected at pH 3.0 both with tritiated cutin and with p-nitrophenyl butyrate (relative activity of 25 %) as the substrates. ScCut1 showed activity towards shorter (C2 to C3) fatty acid esters of p-nitrophenol than towards longer ones. Circular dichroism analysis suggested that the denaturation of ScCut1 by heating the protein sample to 80 °C was to a great extent reversible.

Displaying Candida antarctica lipase B on the cell surface of Aspergillus niger as a potential food-grade whole-cell catalyst

Aspergillus niger is a recognized workhorse used to produce food processing enzymes because of its extraordinarily high protein-producing capacity. We have developed a new cell surface display system de novo in A. niger using expression elements from generally recognized as safe certified microorganisms. Candida antarctica lipase B (CALB), a widely used hydrolase, was fused to an endogenous cell wall mannoprotein, CwpA, and functionally displayed on the cell surface. Localization of CALB was confirmed by enzymatic assay and immunofluorescence analysis using laser scanning confocal microscopy. After induction by maltose for 45 h, the hydrolytic activity and synthesis activity of A. niger mycelium-surface displayed CALB (AN-CALB) reached 400 and 240 U/g dry cell, respectively. AN-CALB was successfully used as a whole-cell catalyst for the enzymatic production of ethyl esters from a series of fatty acids of different chain lengths and ethanol. In a solvent-free system, AN-CALB showed great synthetic activity and afforded high substrate mole conversions, which amounted to 87 % for ethyl hexanoate after 2 h, 89 % for ethyl laurate after 2 h, and 84 % for ethyl stearate after 3 h. These results suggested that CwpA can act as an efficient anchoring motif for displaying enzyme on A. niger, and AN-CALB is a robust, green, and cost-effective alternative food-grade whole-cell catalyst to commercial lipase.