Molecular characterization of laccase genes from the basidiomycete Trametes hirsuta Bm-2 and analysis of the 5' untranslated region (5'UTR)

The aim of this study was to identify and characterize laccase genes produced by Trametes hirsuta Bm-2 in a liquid medium, both with and without induction. The amplification of 5'and 3'regions of laccase sequences was obtained by the RACE-PCR method, and these were assembled to obtain a cDNA of total length. Two new laccase genes were isolated from basal medium (lac-B) and lignocellulosic grapefruit substrate (lac-T), both encoding open reading frames of 2566 bp. Both laccase-predicted proteins consisted of 521 amino acids, four copper-binding regions, a signal peptide, and five potential glycosilation sites (Asn-Xaa-Ser/Tre). Moreover, the deduced amino acid sequences share about 76-85% identity with other laccases of WRF. Sequence comparison showed 47 synonymous point mutations between lac-B and lac-T. In addition, 5' untranslated regions (UTR) of laccase genes lac-B and lac-T showed differences in length and number of regulatory elements that may affect transcriptional or translational expression of these genes.

Expression of a new laccase from Moniliophthora roreri at high levels in Pichia pastoris and its potential application in micropollutant degradation

Laccases have gained significant attention due to their emerging applications including bioremediation, biomass degradation and biofuel cells. One of the prerequisites for the industrial application of laccases is their sufficient availability. However, expression levels of recombinantly expressed laccases are often low. In this study Mrl2, a new laccase from the basidiomycete Moniliophthora roreri, was cloned in Pichia pastoris and produced in an optimized fed-batch process at an exceptionally high yield of 1.05 g l⁻¹. With a redox potential of 0.58 V, Mrl2 belongs to mid-redox potential laccases. However, Mrl2 demonstrated high k_cat values of 316, 20, 74, and 36 s⁻¹ towards 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), syringaldazine (SGZ), 2,6-dimethoxyphenol (2,6-DMP) and guaiacol, respectively. Mrl2 remained stable above pH 6 and in the presence of many metal ions, which is important for application in bioremediation. Mrl2 was investigated for the ability to degrade endocrine disrupting chemicals (EDCs) and non-steroidal anti-inflammatory drugs (NSDAIs) at neutral pH value. The enzyme accepted and converted estrone, 17β-estradiol, estriol, the synthetic contraceptive 17α-ethinyl estradiol and bisphenol A at pH 7 faster than high-potential laccases from Trametes versicolor. For example, within 30 min Mrl2 removed more than 90% bisphenol A, 17ß-estradiol, 17α-ethinyl estradiol and estriol, respectively. The concentration of the recalcitrant drug diclofenac dropped by 56% after 20 h incubation with Mrl2.

Lignocellulose degrading extremozymes produced by Pichia pastoris: current status and future prospects

In this review article, extremophilic lignocellulosic enzymes with special interest on xylanases, β-mannanases, laccases and finally cellulases, namely, endoglucanases, exoglucanases and β-glucosidases produced by Pichia pastoris are reviewed for the first time. Recombinant lignocellulosic extremozymes are discussed from the perspectives of their potential application areas; characteristics of recombinant and native enzymes; the effects of P. pastoris expression system on recombinant extremozymes; and their expression levels and applied strategies to increase the enzyme expression yield. Further, effects of enzyme domains on activity and stability, protein engineering via molecular dynamics simulation and computational prediction, and site-directed mutagenesis and amino acid modifications done are also focused. Superior enzyme characteristics and improved stability due to the proper post-translational modifications and better protein folding performed by P. pastoris make this host favourable for extremozyme production. Especially, glycosylation contributes to the structure, function and stability of enzymes, as generally glycosylated enzymes produced by P. pastoris exhibit better thermostability than non-glycosylated enzymes. However, there has been limited study on enzyme engineering to improve catalytic efficiency and stability of lignocellulosic enzymes. Thus, in the future, studies should focus on protein engineering to improve stability and catalytic efficiency via computational modelling, mutations, domain replacements and fusion enzyme technology. Also metagenomic data need to be used more extensively to produce novel enzymes with extreme characteristics and stability.