Effect of tunicamycin on N-acetyl-beta-D-glucosaminidase produced by Trichoderma harzianum

Purification, identification and characterization of Nag2 N-acetylglucosaminidase from Trichoderma virens strain mango

BACKGROUND

N-acetylglucosaminidase (NAGase) could liberate N-acetylglucosamine (GlcNAc) from GlcNAc-containing oligosaccharides. Trichoderma spp. is an important source of chitinase, particularly NAGase for industrial use. nag1 and nag2 genes encoding NAGase, are found in the genome in Trichoderma spp. The deduced Nag1 and Nag2 shares ~ 55% homology in Trichoderma virens. Most studies were focus on Nag1 and nag1 previously.

RESULTS

The native NAGase (TvmNAG2) was purified to homogeneity with molecular mass of ~ 68 kDa on SDS-PAGE analysis, and identified as Nag2 by MALDI/MS analysis from an isolate T. virens strain mango. RT-PCR analyses revealed that only nag2 gene was expressed in liquid culture of T. virens, while both of nag1 and nag2 were expressed in T. virens cultured on the plates. TvmNAG2 was thermally stable up to 60 °C for 2 h, and the optimal pH and temperature were 5.0 and 60-65 °C, respectively, using p-nitrophenyl-N-acetyl-β-D-glucosaminide (pNP-NAG) as substrate. The hydrolytic product of colloidal chitin by TvmNAG2 was suggested to be GlcNAc based on TLC analyses. Moreover, TvmNAG2 possesses antifungal activity, inhibiting the mycelium growth of Sclerotium rolfsii. And it was resistant to the proteolysis by papain and trypsin.

CONCLUSIONS

The native Nag2, TvmNAG2 was purified and identified from T. virens strain mango, as well as enzymatic properties. To our knowledge, it is the first report with the properties of native Trichoderma Nag2.

A combined approach for improving alkaline acetyl xylan esterase production in Pichia pastoris, and effects of glycosylation on enzyme secretion, activity and stability

High level expression of axe1, a gene previously cloned from Volvariella volvacea that encodes an acetyl xylan esterase with two potential N-linked glycosylation sites, has been achieved in Pichia pastoris using a codon-optimized axe1 synthesized by the primer extension PCR procedure. The GC content of the codon-optimized axe1 was 48.62% compared with 55.49% in the native gene. Using the codon-optimized construct, AXE1 expression in P. pastoris was increased from an undetectable level to 136.45 U/ml six days after induction of yeast cultures grown in BMMY medium. A further increase (to 463 U/ml) was achieved when conditions for yeast culture were optimized as follows: 2.8% methanol, 0.63% casamino acids, and pH 8.0. This latter value represented a 3.4-fold and 246-fold increase in the enzyme levels recorded in non-optimized P. pastoris cultures and in rice straw-grown cultures of V. volvacea, respectively. N-linked glycosylation played an essential role in AXE1 secretion but had only a slight effect on the catalytic activity and stability of the recombinant enzyme.

Influence of N-glycosylation on the morphogenesis and growth of Paracoccidioides brasiliensis and on the biological activities of yeast proteins

The fungus Paracoccidioides brasiliensis is a human pathogen that causes paracoccidioidomycosis, the most prevalent systemic mycosis in Latin America. The cell wall of P. brasiliensis is a network of glycoproteins and polysaccharides, such as chitin, that perform several functions. N-linked glycans are involved in glycoprotein folding, intracellular transport, secretion, and protection from proteolytic degradation. Here, we report the effects of tunicamycin (TM)-mediated inhibition of N-linked glycosylation on P. brasiliensis yeast cells. The underglycosylated yeasts were smaller than their fully glycosylated counterparts and exhibited a drastic reduction of cell budding, reflecting impairment of growth and morphogenesis by TM treatment. The intracellular distribution in TM-treated yeasts of the P. brasiliensis glycoprotein paracoccin was investigated using highly specific antibodies. Paracoccin was observed to accumulate at intracellular locations, far from the yeast wall. Paracoccin derived from TM-treated yeasts retained the ability to bind to laminin despite their underglycosylation. As paracoccin has N-acetyl-β-d-glucosaminidase (NAGase) activity and induces the production of TNF-α and nitric oxide (NO) by macrophages, we compared these properties between glycosylated and underglycosylated yeast proteins. Paracoccin demonstrated lower NAGase activity when underglycosylated, although no difference was detected between the pH and temperature optimums of the two forms. Murine macrophages stimulated with underglycosylated yeast proteins produced significantly lower levels of TNF-α and NO. Taken together, the impaired growth and morphogenesis of tunicamycin-treated yeasts and the decreased biological activities of underglycosylated fungal components suggest that N-glycans play important roles in P. brasiliensis yeast biology.

Regulation of N-acetyl-beta-D-glucosaminidase produced by Trichoderma harzianum: evidence that cAMP controls its expression

Trichoderma harzianum is a filamentous fungus reported to be a producer of extracellular N-acetyl-beta-D-glucosaminidase (NAGase) when grown in chitin-containing medium. An approximately 64-kDa protein with NAGase activity was purified by gel filtration and ion exchange chromatography. The involvement of cyclic AMP (cAMP) in the synthesis of NAGase from T. harzianum in chitin-containing medium was also investigated. Molecules that increase the intracellular levels of cAMP, including caffeine, aluminium tetrafluoride and dinitrophenol, were used. Western blot analysis showed that NAGase synthesis was repressed by increasing the levels of intracellular cAMP. Using specific nag primers in a reverse transcription-polymerase chain reaction-based approach, NAGase synthesis was shown to be regulated at the level of gene transcription.