Characterization of Melanocarpus albomyces steryl esterase produced in Trichoderma reesei and modification of fibre products with the enzyme

Debarking, pitch removal and retting: Role of microbes and their enzymes

Microbial enzymes are green and clean alternatives for several processes in the pulp and paper industry. Enzyme treatment decreases the energy requirement and minimizes the wood losses during drum debarking. Lipophilic wood extractives are known as pitch. Pitch deposition adversely affects the pulp quality and increases equipment maintenance and operating costs during paper manufacturing. Several chemical additives have been used to remove pitch deposits. Natural seasoning of wood is used to minimize pitch content in wood, but it has some disadvantages including yield losses and decreased brightness. Controlled seasoning with white-rot fungi or albino strains of sapstain fungi is an effective tool for degradation and removal of wood extractives. Enzymes including lipase, laccase, sterol esterase, and lipooxygenase have also been used to minimize pitch-related problems. Enzymatic retting has been proved an eco-friendly and economical solution for chemical degumming and traditional retting.

Surface engineering of polyester-degrading enzymes to improve efficiency and tune specificity

Certain members of the carboxylesterase superfamily can act at the interface between water and water-insoluble substrates. However, nonnatural bulky polyesters usually are not efficiently hydrolyzed. In the recent years, the potential of enzyme engineering to improve hydrolysis of synthetic polyesters has been demonstrated. Regions on the enzyme surface have been modified by using site-directed mutagenesis in order to tune sorption processes through increased hydrophobicity of the enzyme surface. Such modifications can involve specific amino acid substitutions, addition of binding modules, or truncation of entire domains improving sorption properties and/or dynamics of the enzyme. In this review, we provide a comprehensive overview on different strategies developed in the recent years for enzyme surface engineering to improve the activity of polyester-hydrolyzing enzymes.

Synergistic effect of mutagenesis and truncation to improve a polyesterase from Clostridium botulinum for polyester hydrolysis

The activity of the esterase (Cbotu_EstA) from Clostridium botulinum on the polyester poly(ethylene terephthalate) (PET) was improved by concomitant engineering of two different domains. On the one hand, the zinc-binding domain present in Cbotu_EstA was subjected to site-directed mutagenesis. On the other hand, a specific domain consisting of 71 amino acids at the N-terminus of the enzyme was deleted. Interestingly, a combination of substitution of residues present in the zinc-binding domain (e.g. S199A) synergistically increased the activity of the enzyme on PET seven fold when combined to the truncation of 71 amino acids at the N-terminus of the enzyme only. Overall, when compared to the native enzyme, the combination of truncation and substitutions in the zinc-binding domain lead to a 50-fold activity improvement. Moreover, analysis of the kinetic parameters of the Cbotu_EstA variants indicated a clear shift of activity from water soluble (i.e. para-nitrophenyl butyrate) to insoluble polymeric substrates. These results evidently show that the interaction with non-natural polymeric substrates provides targets for enzyme engineering.

A statistical approach for optimization of alkaline lipase production by ascidian associated-Halobacillus trueperi RSK CAS9

A marine ascidian-associated bacterium, Halobacillus trueperi RSK CAS9, was optimized for lipase production by response surface methodology using marine waste as substrate. The central composite design was employed, and the optimal medium constituents for maximum lipase production (1355.81 U/ml) were determined to be tuna powder (14.58 g/l), olive oil (5.05 ml/l); NaCl (72.42 g/l), temperature (45 °C) and pH 9.0. An alkaline lipase was purified to 8.46 fold with 1193.59 U mg⁻¹ specific activities with the molecular weight of 44 kDa. The activity was substantially inhibited by EDTA and PMSF, indicating that it was a metalloenzyme serine residue which was essential for catalytic activity. Thus, lipase production by microbial conversion of marine fish wastes in this study suggested its potential utilization for the production of high value products.

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.