Purificação e caracterização de uma xilanase halotolerante de Aspergillus hortai CRM 1919 e aplicação na hidrólise de subprodutos agroindustriais
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Data
2018-02-26
Autores
Gracioli, Michel Ricardo [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As enzimas xilanases são de grande interesse biotecnológico em função da sua habilidade na degradação da molécula de xilana, a principal hemicelulose presente na parede celular de plantas. Tais enzimas encontram aplicações nos mais diversos ramos da indústria como na produção de alimentos e bebidas, de cosméticos, de ração animal, de biocombustíveis entre outros. Em razão da sua composição química, os subprodutos lignocelulósicos, produzidos em grande quantidade pela agroindústria, se apresentam como uma potencial fonte sustentável para a produção de valiosos compostos como biocombustíveis, fertilizantes, rações, produtos químicos e enzimas. Assim, tendo em vista esse contexto, foi desenvolvido o presente trabalho, cujo objetivo foi caracterizar e purificar a principal endoxilanase produzida por uma linhagem de Aspergillus hortai cultivado em estado sólido e aplicá-la, nas formas bruta e purificada, na hidrólise de subprodutos agroindustriais. A purificação da enzima foi alcançada após três etapas cromatográficas, respectivamente, uma cromatografia de troca iônica seguida por cromatografias de interação hidrofóbica e exclusão molecular. Ao final das etapas, a enzima purificada apresentou recuperação de 1,1% e fator de purificação de 15,8 vezes. A enzima bruta e purificada se mostrou tolerante ao NaCl na presença de até 4 M do sal. Por outro lado, foi pouco tolerante à presença de íons e alguns compostos como Hg2+, Cu2+, SDS, Triton X-100 e TWEEN 20/80. Em contrapartida, DTT e β-mercaptoetanol a 10 mM estimularam a atividade da enzima bruta em 13 e 19%, respectivamente. Para a enzima bruta, a temperatura e pH ótimos de reação foram, respectivamente, 60 °C e 6,0 tanto na ausência quanto na presença de NaCl 0,5 e 2,5 M. Apresentou boa estabilidade térmica a 40 °C na ausência de NaCl, e foi ativada na presença de 0,5 M e 2,5 M do sal durante as 4 h de incubação. A enzima bruta e purificada foi estável em uma ampla faixa de pHs (3,0-8,0) na ausência e na presença de NaCl e apresentou alta especificidade pelas xilanas birchwood, beechwood e oat spelt, não tendo sido detectadas atividades endoglucanase sobre CMC, exoglucanase em Avicel e β-xilosidase em ρNPX. Após a purificação, os perfis de temperatura e pH ótimos de reação se mantiveram em 60 °C e 6, respectivamente. A enzima pura foi, também, bastante estável a temperatura de 40 °C, mantendo mais de 50% da atividade controle durante as 4 h de incubação, e ao pH, variando de 3,0-8,0, na ausência e na presença de NaCl. Xilobiose e xilo-oligossacarídeos superiores foram os produtos formados na hidrólise da xilana oat spelt pela enzima purificada, sugerindo ação enzimática do tipo endoxilanase. A massa molecular aparente, após a purificação, foi estimada em 25,0 kDa por SDS-PAGE e em 14,8 kDa por exclusão molecular. Os parâmetros cinéticos Km e Vmáx em xilana de beechwood sofreram variações em resposta a presença de NaCl, sendo a maior eficiência catalítica obtida na presença de 2,5 M do sal (kcat/km 40,91). A análise da composição química dos subprodutos - sabugo, palha e folha de milho - revelou, respectivamente, 25,6%, 45,3% e 34,9% de carboidratos, 19,7%, 15,2% e 17,6% de lignina e 9,0%, 17,4% e 24,0% de extrativos para a biomassa in natura e, 33,3%, 25,2% e 38,8% de carboidratos e 6,5%, 8,9% e 12,3% de lignina para a xilana extraída desses subprodutos. A extração das hemiceluloses utilizando tratamento alcalino oxidativo resultou em um rendimento de 64% para o sabugo, 18% para a palha e 50% para a folha. A enzima bruta e purificada foi capaz de hidrolisar as biomassas na forma in natura, bem como as xilanas extraídas desse material produzindo majoritariamente xilopentoses e xilohexoses. Sendo assim, pode-se afirmar que a xilanase bruta e purificada em estudo apresentou propriedades interessantes para a aplicação industrial, especialmente na produção de xilo-oligossacarídeos e em processos conduzidos sob elevada salinidade.
Xylanases raise a biotechnological interest due to its ability to degrade xylan. Such enzymes find use in a variety of industrial processes such as the production of food and beverage, cosmetics, animal feed, second generation ethanol, among many others. As for its chemical composition, lignocellulosic byproducts, widely produced by agroindustry, presents itself as a potential sustainable source for production of valuable composts like soil fertilizers, animal feed, chemical products and enzymes. In this context, the main xylanase produced by an Aspergillus hortae strain, cultivated in solid state (SSF), was characterized, purified and applied in the hydrolysis of hemicellulose from corn by-products. Enzyme purification was achieved after three chromatographyc steps, respectively, an ion exchange chromatography followed by hydrophobic interaction and molecular exclusion chromatographys. After the purification steps, a final yield of 1.1% and purification fold of 15.8 was achieved. Both crude and purified enzyme showed high tolerance to NaCl in the presence of up to 4 M of the salt. The enzyme displayed a very low tolerance to some metal ions and chemical compounds, especially Hg2+, Cu2+, SDS, Triton X-100 and TWEEN 20/80. On the other hand, DTT and β- mercaptoetanol at 10 mM stimulated crude enzyme activity in 13% and 19%, respectively. As for the crude enzyme, optimum temperature and pH were, respectively, 60 °C and 6.0, in the absence and presence of 0.5 and 2.5 M NaCl. It showed good thermal stability at 40 °C in the absence of NaCl and was activated in the presence of 0.5 and 2.5 M of the salt throughout the 4 h incubation time. Crude and purified enzyme was also stable over a wide pH range (3.0 - 8.0) both in the absence and presence of NaCl and presented high specificity for birchwood, beechwood and oat spelt xylans, not showing detectable endoglucanase, exoglucanase and β- xylosidase activities. After purification, optimum temperature and pH profiles remained at 60 °C and 6.0, respectively. Purified enzyme showed good stability at 40 °C, being able to retain more than 50% of the control activity during 4 h of incubation, and to the pH, varying from 3.0 to 8.0, in the absence and in the presence of NaCl. Xylobiose and xilooligosaccharides were the products of oat spelt xylan hydrolysis by the purified enzyme, suggesting an endoxilanase mode of action. The apparent molecular mass, after purification, was estimated to be 25.0 kDa by SDS-PAGE and 14.8 kDa by exclusion chromatography. Kinetic parameters of Km and Vmáx using beechwood xylan were 5.12 mg/mL and 14.25 μmol/min.mL, respectively, in the absence of NaCl, 9.56 mg/mL and 20.80 μmol/min.mL in the presence of 0.5 M and 3.13 mg/mL and 9.22 μmol/min.mL in the presence of 2.5 M of the same salt. Chemical analysis of the biomasses from corn cob, stover and leaves, revealed a composition of, respectively, 25.6%, 45.3%, 34.9% carbohydrates, 19.7%, 15.2%, 17.6% lignin and 9.0%, 17.4%, 24.0% extractives for in natura biomasses and 33.3%, 25.2%, 38.8% carbohydrates and 6.5%, 8.9%, 12.3% lignin for the extracted hemicelluloses. Hemicellulose extraction yields were of 64% for corn cob, 18% for stover and 50% for leaves. Both crude and purified enzyme was capable of hydrolyzing in natura biomasses, as well as the extracted hemicelluloses from these materials, producing mainly xylopentoses and xyloheoses. In summary, the xylanase presented attractive properties for industrial applications, especially in the production of xyloolygossacharides and in those carried out under high NaCl concentration.
Xylanases raise a biotechnological interest due to its ability to degrade xylan. Such enzymes find use in a variety of industrial processes such as the production of food and beverage, cosmetics, animal feed, second generation ethanol, among many others. As for its chemical composition, lignocellulosic byproducts, widely produced by agroindustry, presents itself as a potential sustainable source for production of valuable composts like soil fertilizers, animal feed, chemical products and enzymes. In this context, the main xylanase produced by an Aspergillus hortae strain, cultivated in solid state (SSF), was characterized, purified and applied in the hydrolysis of hemicellulose from corn by-products. Enzyme purification was achieved after three chromatographyc steps, respectively, an ion exchange chromatography followed by hydrophobic interaction and molecular exclusion chromatographys. After the purification steps, a final yield of 1.1% and purification fold of 15.8 was achieved. Both crude and purified enzyme showed high tolerance to NaCl in the presence of up to 4 M of the salt. The enzyme displayed a very low tolerance to some metal ions and chemical compounds, especially Hg2+, Cu2+, SDS, Triton X-100 and TWEEN 20/80. On the other hand, DTT and β- mercaptoetanol at 10 mM stimulated crude enzyme activity in 13% and 19%, respectively. As for the crude enzyme, optimum temperature and pH were, respectively, 60 °C and 6.0, in the absence and presence of 0.5 and 2.5 M NaCl. It showed good thermal stability at 40 °C in the absence of NaCl and was activated in the presence of 0.5 and 2.5 M of the salt throughout the 4 h incubation time. Crude and purified enzyme was also stable over a wide pH range (3.0 - 8.0) both in the absence and presence of NaCl and presented high specificity for birchwood, beechwood and oat spelt xylans, not showing detectable endoglucanase, exoglucanase and β- xylosidase activities. After purification, optimum temperature and pH profiles remained at 60 °C and 6.0, respectively. Purified enzyme showed good stability at 40 °C, being able to retain more than 50% of the control activity during 4 h of incubation, and to the pH, varying from 3.0 to 8.0, in the absence and in the presence of NaCl. Xylobiose and xilooligosaccharides were the products of oat spelt xylan hydrolysis by the purified enzyme, suggesting an endoxilanase mode of action. The apparent molecular mass, after purification, was estimated to be 25.0 kDa by SDS-PAGE and 14.8 kDa by exclusion chromatography. Kinetic parameters of Km and Vmáx using beechwood xylan were 5.12 mg/mL and 14.25 μmol/min.mL, respectively, in the absence of NaCl, 9.56 mg/mL and 20.80 μmol/min.mL in the presence of 0.5 M and 3.13 mg/mL and 9.22 μmol/min.mL in the presence of 2.5 M of the same salt. Chemical analysis of the biomasses from corn cob, stover and leaves, revealed a composition of, respectively, 25.6%, 45.3%, 34.9% carbohydrates, 19.7%, 15.2%, 17.6% lignin and 9.0%, 17.4%, 24.0% extractives for in natura biomasses and 33.3%, 25.2%, 38.8% carbohydrates and 6.5%, 8.9%, 12.3% lignin for the extracted hemicelluloses. Hemicellulose extraction yields were of 64% for corn cob, 18% for stover and 50% for leaves. Both crude and purified enzyme was capable of hydrolyzing in natura biomasses, as well as the extracted hemicelluloses from these materials, producing mainly xylopentoses and xyloheoses. In summary, the xylanase presented attractive properties for industrial applications, especially in the production of xyloolygossacharides and in those carried out under high NaCl concentration.
Descrição
Palavras-chave
Endoxilanase, Purificação, Caracterização, Aspergillus hortai, Halotolerancia, Hidrolise enzimática, Xilana, Subproduto agroindustrial, Endoxylanase, Purification, Characterization, Halotolerance, Hidrolysis, Xylan, Agroindustrial by-products