RESUMO
BACKGROUND: The search for novel thermostable xylanases for industrial use has intensified in recent years, and thermophilic fungi are a promising source of useful enzymes. The present work reports the heterologous expression and biochemical characterization of a novel thermostable xylanase (GH10) from the thermophilic fungus Malbranchea pulchella, the influence of glycosylation on its stability, and a potential application in sugarcane bagasse hydrolysis. RESULTS: Xylanase MpXyn10A was overexpressed in Aspergillus nidulans and was active against birchwood xylan, presenting an optimum activity at pH 5.8 and 80°C. MpXyn10A was 16% glycosylated and thermostable, preserving 85% activity after 24 hours at 65°C, and deglycosylation did not affect thermostability. Circular dichroism confirmed the high alpha-helical content consistent with the canonical GH10 family (ß/α)8 barrel fold observed in molecular modeling. Primary structure analysis revealed the existence of eight cysteine residues which could be involved in four disulfide bonds, and this could explain the high thermostability of this enzyme even in the deglycosylated form. MpXyn10A showed promising results in biomass degradation, increasing the amount of reducing sugars in bagasse in natura and in three pretreated sugarcane bagasses. CONCLUSIONS: MpXyn10A was successfully secreted in Aspergillus nidulans, and a potential use for sugarcane bagasse biomass degradation was demonstrated.
RESUMO
The effect of several nutritional and environmental parameters on growth and amylase production from Rhizopus microsporus var. rhizopodiformis was analysed. This fungus was isolated from soil of the Brazilian «cerrado» and produced high levels of amylolytic activity at 45 degrees C in liquid medium supplemented with starch, sugar cane bagasse, oat meal or cassava flour. Glucose in the culture medium drastically repressed the amylolytic activity. The products of hydrolysis were analysed by thin layer chromatography, and glucose was detected as the main component. The amylolytic activity hydrolysed several substrates, such as amylopectin, amylase, glycogen, pullulan, starch, and maltose. Glucose was always the main end product detected by high-pressure liquid chromatography analysis. These results indicated that the amylolytic activity studied is a glucoamylase, but there were also low levels of alpha-amylase. As compared to other fungi, R. microsporus var. rhizopodiformis can be considered an efficient producer of thermostable amylases, using raw residues of low cost as substrates. This information is of technological value, considering the importance of amylases for industrial hydrolysis (AU)
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