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| Author(s): |
Viviane Isabel Serpa
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) |
| Defense date: | 2012-05-02 |
| Examining board members: |
Igor Polikarpov;
Ilana Lopes Baratella da Cunha Camargo;
Andrei Leitão;
Flávio Henrique da Silva;
Richard John Ward
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| Advisor: | Igor Polikarpov |
| Abstract | |
Cellulases have attracted an outstanding interest in the recent years because of its ability in the bioconversion of cellulose-containing raw materials into glucose, which can then be converted into ethanol by fermentation. The cellulase complex able to degrade cellulose consists of several enzymes (mainly cellulases and β-glucosidases) and auxiliary proteins, which act in synergism to efficiently solubilize the biomass. In this study, we investigated the enzymatic hydrolysis of pretreated sugarcane bagasse using crude enzyme extracts produced by Trichoderma harzianum as well as from the extract in combination with a commercial cocktail. The influence of different levels of biomass delignification, degree of crystallinity of lignicellulose, composition of enzymatic activities and BSA on enzymatic hydrolysis yields was evaluated. Our X-ray diffraction studies showed that crystallinity of lignocellulose is not a key determinant of its recalcitrance toward enzymatic hydrolysis. In fact, under the experimental conditions, an increase in crystallinity of lignocellulosic samples resulted in increased glucose release by enzymatic hydrolysis. Furthermore, under the same conditions, the addition of BSA had no significant effect on enzymatic hydrolysis. The most efficient enzyme blends were obtained by mixing a commercial enzymatic cocktail with T. harzianum cellulase preparations (above 97%). Increased hydrolytic efficiencies appeared to correlate with having an adequate level of both β-glucosidase and xylanase activities in the blends. Due to its elevated cellulolytic activity, the filamentous fungus T. harzianum has a considerable potential in biomass hydrolysis applications. The cellobiohydrolase I, an exoglucanase, is the main enzyme secreted by this fungus (about 60% of total) and in this study we have expressed, purified and performed an initial biochemical, biophysical and structural characterization. As confirmed by small angle X-ray scattering (SAXS) both full-length CBHI and its catalytic core domain (CCD), obtained by partial digestion with papain, are monomeric in solution and they have Dmax of 110 and 60 Å, and Rg of 20 and 27 Å, respectively. The results indicate that the linker is flexible in solution and confirmed the tadpole shape of the enzyme. CBHI displays maximum activity at pH 5.0 and temperature of 50 °C, with specific activities against Avicel ® and pNPC of 0,28 and 1.53 U/mg, respectively. Other celulases were also expressed, however, for them we have used the heterologous expression system in Aspergillus niger and Pichia pastoris. The catalytic domain of endoglucanase I from T. harzianum was expressed in A. niger and partially characterized. The protein has specific activity against CMC of 15.8 U/mg and optimum pH and temperature of 3 and 50 °C, respectively. The protein is stable in these conditions until 3 days of incubation. Biophysical studies of termal shift and circular dichroism (CD) assays have showed some parameters of stability of tertiary and secondary structure of the protein. It loses regulary terciary structure in pH 5 around 30 °C but the secondary structure is desordened only in pH 9 at 25 °C. CD experiments also indicated the secondary structure compsition of the catalytic domain of EGLI: 6% de α-helices and 42% de β-sheet. (AU) | |
| FAPESP's process: | 07/08706-9 - Molecular and Structural Studies of Cellulitic Complex Enzymes of Fungi Trichoderma harzianum with Potencial of Enzymatic Transformation of Biomass |
| Grantee: | Viviane Isabel Serpa |
| Support Opportunities: | Scholarships in Brazil - Doctorate |