Arachidonic acid (AA) has a wide range of applications in medicine, pharmacology, diet, infant nutrition, and agriculture, due to its unique biological properties. The microbiological processes involved in AA production usually require carbohydrate substrates. In this paper, we propose a method for AA production from glycerol, an inexpensive and renewable carbon substrate that is produced by the fungal strain, Mortierella alpina NRRL-A-10995. Our experimental results showed that the optimum pH values required for fungal growth and the production of lipids and AA were different and depended on the growth phase of the fungus. The AA production was shown to be extremely sensitive to acidic pH values and was completely inhibited at a pH of 3.0. The optimum temperature for AA production was 20-22 • C. Continuous cultivation of M. alpina occurred in a glycerol-containing medium, and growth limitations were implemented through the addition of nitrogen and the selection of optimal conditions (pH 6.0, 20 • C). This ensured that active AA production occurred (25.2% of lipids and 3.1% of biomass), with the product yield from the consumed glycerol being 1.6% by mass and 3.4% by energy.
Endoglucanases (EGLs) are important components of multienzyme cocktails used in the production of a wide variety of fine and bulk chemicals from lignocellulosic feedstocks. However, a low thermostability and the loss of catalytic performance of EGLs at industrially required temperatures limit their commercial applications. A structure-based disulfide bond (DSB) engineering was carried out in order to improve the thermostability of EGLII from Penicillium verruculosum. Based on in silico prediction, two improved enzyme variants, S127C-A165C (DSB2) and Y171C-L201C (DSB3), were obtained. Both engineered enzymes displayed a 15–21% increase in specific activity against carboxymethylcellulose and β-glucan compared to the wild-type EGLII (EGLII-wt). After incubation at 70 °C for 2 h, they retained 52–58% of their activity, while EGLII-wt retained only 38% of its activity. At 80 °C, the enzyme-engineered forms retained 15–22% of their activity after 2 h, whereas EGLII-wt was completely inactivated after the same incubation time. Molecular dynamics simulations revealed that the introduced DSB rigidified a global structure of DSB2 and DSB3 variants, thus enhancing their thermostability. In conclusion, this work provides an insight into DSB protein engineering as a potential rational design strategy that might be applicable for improving the stability of other enzymes for industrial applications.
Endoglucanase IIa from Penicillium verruculosum (PvCel5A) has three potential N-glycosylation sites: Asn19, Asn42 and Asn194. In order to study the role of N-glycosylation, the wild type (wt) PvCel5A and its mutant forms, carrying Asn to Ala substitutions, were cloned into Penicillium canescens All forms of the rPvCel5A were successfully expressed and purified for characterization. The MALDI-TOF mass spectrometry peptide fingerprinting showed that N-glycans linked to Asn42 and Asn194 represent variable oligosaccharides, according to the formula (Man)(GlcNAc) No evidence for Asn19 glycosylation was found. Mutations had no notable effect on the enzyme thermostability; however, the N-linked glycans stabilized the enzyme against proteolytic attack. For N42A and N194A mutants, a slight shift of pH-optimum to pH 5.0 was observed (from pH-optimum of 4.5 for the native enzyme, rPvCel5A-wt and N19A mutant). The N19A mutation led to a notable decrease in the specific activity against carboxymethylcellulose and barley β-glucan (by 26% and 12% relative to the rPvCel5A-wt), while the N42A and N194A mutants displayed 12-13% and 32-35% increase in the activities. Similar effects of the mutations were observed in prolonged hydrolysis of β-glucan and milled aspen wood by rPvCel5A forms in the presence of purified β-glucosidase.
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