Characterization of novel cholesterol esterase from Trichoderma sp. AS59 with high ability to synthesize steryl esters

Biochemical Characterization of a Lipolytic Enzyme From Aspergillus oryzae That Hydrolyzes Triacylglycerol and Sterol Esters

A novel lipolytic enzyme-encoding gene, lipO745, from Aspergillus oryzae RIB40 was cloned and expressed in Pichia pastoris. Purified recombinant LipO745 (rLipO745) had a molecular mass of approximately 60 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. rLipO745 exhibited maximum activity at 40 °C and pH 7.0 and was stable at temperatures ≤ 40 °C. The substrate specificity of purified rLipO745 was analyzed using α-naphthyl esters as artificial substrates and various triacylglycerol and sterol esters as natural substrates. From among a panel of α-naphthyl esters (C2-C16), α-naphthyl butyrate (C4), with an activity of 269 ± 3.3 units/mg protein, was the optimal substrate for hydrolysis by the purified recombinant protein. The K_m and k_cat values of rLiO745 for the C4 substrate were 0.073 ± 0.0012 mM and 608 ± 108 s^-1, respectively. The purified recombinant enzyme had considerable hydrolytic activity toward tributyrin, tripalmitin, and triolein, indicating lipase activity, and toward cholesteryl acetate, butyrate, palmitate, and oleate, indicating sterol esterase activity. Transesterification activities between tributyrin and cholesterol or between tributyrin and campesterol were also determined.

Improvement of the Activity of a Fungal Versatile-Lipase Toward Triglycerides: An in silico Mechanistic Description

Some enzymes that belong to the Candida rugosa-like lipase family (abH03. 01) combine the activities of lipases and sterol esterases. Thus, they can act on water-insoluble carboxylic esters releasing long-chain fatty acids but also on sterol esters, although with different activity and affinity. The differences in the catalytic properties among the proteins of this family are explained by small changes in the hydrophobicity of some regions. One of such versatile enzymes is the sterol esterase/lipase from Ophiostoma piceae (OPE) that acts very efficiently on the two types of substrates. Structurally, OPE is characterized by the presence of a lid formed by a α-helix and two 3₁₀-helices rich in hydrophobic amino acids. In this study, the ope gene was modified by directed mutagenesis in order to change specific amino acids in the lid region to modify its structure with the aim of increasing its hydrophobicity. Several recombinant forms of OPE were heterologously produced in Pichia pastoris. In silico molecular dynamics simulations have been used to decipher the mechanistic principles behind the improvements in substrate catalysis. The analyses suggested that the enhanced activity toward hydrophobic substrates such as triglycerides could be due to a better stabilization of the substrate in the lid region as a result of an increased hydrophobicity and an improved topology. These results indicate that in silico simulations can be useful for the optimization of the activity of lipases from the C. rugose-like family for different biotechnological applications.

Production of a sterol esterase from Ophiostoma piceae in batch and fed-batch bioprocesses using different Pichia pastoris phenotypes as cell factory

The potential biotechnological applications for the Ophiostoma piceae sterol esterase (OPE) are conditioned to the availability of high enzyme amounts at low prices. This enzyme is a versatile biocatalyst with different biotechnological applications. In this work a systematic study on its heterologous production in different Pichia pastoris strains and operational strategies is presented. The best results were obtained using an AOX1 defective yeast strain in a fed-batch bioprocess using methanol as inducer substrate at a set point of 2.5 g L(-1) and sorbitol as cosubstrate by means of a preprogramed exponential feeding rate at a μ = 0.02 h(-1) , reaching 30 U mL(-1) of enzyme and a volumetric productivity of 403.5 U L(-1) h(-1) . These values are twofold higher than those obtained with a Mut(+) phenotype using methanol a sole carbon source. OPE was the main protein secreted by the yeast, 55% for Mut(s) versus 25% for Mut(+.)

Potential of Ophiostoma piceae sterol esterase for biotechnologically relevant hydrolysis reactions

The ascomycete Ophiostoma piceae produces a sterol esterase (OPE) with high affinity toward p-nitrophenol, glycerol, and sterol esters. Recently, this enzyme has been heterologously expressed in the methylotrophic yeast Pichia pastoris under the AOX1 methanol-inducible promoter (PAOX1) using sorbitol as co-susbtrate, and the hydrolytic activity of the recombinant protein (OPE*) turned out to be improved from a kinetic point of view. In this study, we analyze the effects of sorbitol during the expression of OPE*, at first added as an additional carbon source, and methanol as inducer. The O. piceae enzyme was successfully used for PVAc hydrolysis, suggesting its potential applicability in recycled paper production to decrease stickies problems.

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.

Synthesis of fatty acid sterol esters using cholesterol esterase from Trichoderma sp. AS59

We recently reported the characterization of novel cholesterol esterase (EC. 3.1.1.13) from Trichoderma sp. and preliminary work on sterol ester synthesis. In the present study, we further examined the enzyme ability to synthesize cholesterol esters from cholesterol and free fatty acids of various chain lengths, and compared the fatty acid specificity in synthesis with that in hydrolysis. The enzyme catalyzed the synthesis of medium- and long-chain fatty acid cholesterol esters, but failed to synthesize short-chain fatty acid esters. The fatty acid specificities in the synthesis and hydrolysis of cholesterol esters were entirely different from each other. Unlike other lipolytic enzymes, the enzyme was largely independent of water content in the synthesis of cholesterol oleate, and it achieved near-complete esterification in the presence of an equimolar excess of oleic acid. Of additional interest is the finding that the addition of n-hexane markedly enhanced the esterification activities on all the medium- and long-chain saturated fatty acids used. Based on these findings, we attempted to synthesize stigmasterol stearate as a food additive to lower cholesterol levels in blood plasma, and found that the enzyme catalyzed effective synthesis of the ester without the need of dehydration during the reaction, indicating the potential utility of the enzyme in the food industry.