A genomic laccase gene and cDNA were cloned from the white-rot fungi Ganoderma lucidum TR6. The genomic laccase gene contained 2086 bp with nine introns. The laccase cDNA had an open reading frame of 1563 bp. The deduced mature protein consisted of 520 amino acids. Both the genomic laccase gene and cDNA were expressed in the Pichia pastoris GS115. Laccase activities could be detected in transformants with laccase cDNA but not in transformants with genomic laccase gene. The highest activity value reached 685.8 U L(-1). The effects of temperature, pH and nitrogen source on laccase expression in P. pastoris were analyzed. The recombinant laccase was purified and the molecular mass was 73.4 KDa, a little bigger than native laccase. The optimal pH and temperature were specific at pH 3.5 and special range from 60 to 90 °C. The laccase was stable at pH 7.0 and temperature range of 20-30 °C. The Km and Vm values of this recombinant laccase for ABTS were 0.521 mM and 19.65 mM min(-1), respectively.
Squalene synthase (SQS) catalyzes the condensation of two molecules of farnesyl diphosphate to give presqualene diphosphate and the subsequent rearrangement to form squalene. The gene encoding squalene synthase was cloned from Poria cocos by degenerate PCR and inverse PCR. The open reading frame of the gene is 1,497 bp, which encodes 499 amino acid residues. A phylogenetic analysis revealed that P. cocos SQS belonged to the fungus group, and was more closely related to the SQS of Ganoderma lucidum than other fungi. The treatment of P. cocos with methyl jasmonate (MeJA) significantly enhanced the transcriptional level of P. cocos sqs gene and the content of squalene in P. cocos. The transcriptional level of sqs gene was approximately fourfold higher than the control sample and the squalene content reached 128.62 μg/g, when the concentration of MeJA was 300 μM after 72 h induction.
Taxoid 10β-O-acetyl transferase (DBAT) is a key enzyme in the biosynthesis of the famous anticancer drug paclitaxel, which catalyses the formation of baccatin III from 10-deacetylbaccatin III (10-DAB). However, the activity essential residues of the enzyme are still unknown, and the acylation mechanism from its natural substrate 10-deacetylbaccatin III and acetyl CoA to baccatin III remains unclear. In this study, the homology modelling, molecular docking, site-directed mutagenesis, and kinetic parameter determination of the enzyme were carried out. The results showed that the enzyme mutant DBAT resulted in complete loss of enzymatic activity, suggesting that the residue histidine at 162 was essential to DBAT activity. Residues D166 and R363 which were located in the pocket of the enzyme by homology modelling and molecular docking were also important for DBAT activity through the site-directed mutations. Furthermore, four amino acid residues including S31 and D34 from motif SXXD, D372 and G376 from motif DFGWG also played important roles on acylation. This was the first report of the elucidation of the activity essential residues of DBAT, making it possible for the further structural-based re-design of the enzyme for efficient biotransformation of baccatin III and paclitaxel.
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