Publication: Estudio de xilanasas fúngicas para el aprovechamiento de la biomasa lignocelulósica
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2018-08-23
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Universidad Complutense de Madrid
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Abstract
El xilano constituye la segunda mayor reserva de carbono de la biosfera, sólo precedido por la celulosa. Es un heteropolisacárido perteneciente al grupo de las hemicelulosas por lo que está presente en la mayoría de las principales fuentes de biomasa lignocelulósica. Estructuralmente, estos polímeros se caracterizan por tener una cadena principal de unidades de D-xilopiranosa unidas por enlaces β-1,4. Este esqueleto presenta frecuentes acetilaciones y está altamente ramificado, con cadenas laterales muy cortas, formadas por residuos de arabinosa o ácido glucurónico. La abundancia de cada uno de los sustituyentes depende en gran medida del tipo de biomasa vegetal. Debido a esta complejidad su hidrólisis necesita de la acción concertada de toda una batería de enzimas, de entre las cuales las endo-β-1,4-xilanasas y las β-xilosidasas desempañan un papel esencial. Las primeras hidrolizan el polisacárido atacando enlaces internos de la cadena principal, liberando como productos oligosacáridos con distinto grado de polimerización. Las β-xilosidasas son enzimas que completan la degradación, convirtiendo estos xilooligosacáridos (XOS) en xilosa. La importancia económica del aprovechamiento de este heteropolisacárido nace fundamentalmente de su gran abundancia y ha supuesto un fuerte impulso para la investigación sobre ambas enzimas xilanolíticas. La industria busca tanto la sacarificación del xilano, con vistas a la obtención de biocombustibles, como su conversión en productos de alto valor añadido. En este último campo, las endoxilanasas pueden aplicarse para la obtención de XOS, considerados actualmente prebióticos emergentes. En cuanto a las β-xilosidasas, aunque su papel más conocido es el hidrolítico, muchas presentan también la capacidad de transferir un residuo de xilosa a un compuesto aceptor, en una reacción denominada transxilosilación. De esta forma se podrían obtener glicósidos con propiedades bioactivas, abriendo un nuevo campo para la aplicación de estas enzimas...
Xylan represents the second carbon reservoir in the biosphere, only preceded by cellulose. It is a heteropolysaccharide belonging to the group of hemicelluloses, therefore it is a part of most of the main sources of lignocellulosic biomass. Structurally, it is composed by a backbone of β-1,4-linked D-xylopyranosyl units, which is frequently acetylated and highly branched by short side chains of arabinose or glucuronic acid. The abundance of each of these substituents depends largely on the nature of the plant biomass. Due to its complexity, xylan hydrolysis requires the concerted action of multiple enzymes, among which two types of glycosidases, endo-β-1,4-xylanases and β-xylosidases, play the major roles. The former hydrolyze the polysaccharide by attacking internal links in the main chain, releasing oligosaccharides with different polymerization degrees. β-xylosidases end the process by converting these xylooligosaccharides (XOS) into xylose. The economical relevance of exploiting this heteropolysaccharide is based on its great abundance and has driven the research on both xylanolytic enzymes. Industry is interested both in xylan saccharification for obtaining biofuels, and in its conversion into high value-added products. Attending to the latter possibility, endoxylanases can be applied for producing XOS, which are currently considered emerging prebiotics. Regarding to β-xylosidases, many of these glycosidases display the capacity of transferring a xylosyl residue to an acceptor compound, in a reaction called transxylosylation. By this way bioactive glycosides could be obtained, opening a new field for the application of these catalysts. The xylanolytic enzymes are produced in nature mainly by bacteria and fungi for degradation of plant cell wall polysaccharides. Among these organisms, filamentous fungi are the ones which have aroused the greatest interest as producers of these enzymes. The reasons are the higher levels of xylanolytic activities displayed by fungi and the frequent secretion of the desired enzymes to the extracellular medium, which facilitates both the purification and direct use of fungal crudes for several applications...
Xylan represents the second carbon reservoir in the biosphere, only preceded by cellulose. It is a heteropolysaccharide belonging to the group of hemicelluloses, therefore it is a part of most of the main sources of lignocellulosic biomass. Structurally, it is composed by a backbone of β-1,4-linked D-xylopyranosyl units, which is frequently acetylated and highly branched by short side chains of arabinose or glucuronic acid. The abundance of each of these substituents depends largely on the nature of the plant biomass. Due to its complexity, xylan hydrolysis requires the concerted action of multiple enzymes, among which two types of glycosidases, endo-β-1,4-xylanases and β-xylosidases, play the major roles. The former hydrolyze the polysaccharide by attacking internal links in the main chain, releasing oligosaccharides with different polymerization degrees. β-xylosidases end the process by converting these xylooligosaccharides (XOS) into xylose. The economical relevance of exploiting this heteropolysaccharide is based on its great abundance and has driven the research on both xylanolytic enzymes. Industry is interested both in xylan saccharification for obtaining biofuels, and in its conversion into high value-added products. Attending to the latter possibility, endoxylanases can be applied for producing XOS, which are currently considered emerging prebiotics. Regarding to β-xylosidases, many of these glycosidases display the capacity of transferring a xylosyl residue to an acceptor compound, in a reaction called transxylosylation. By this way bioactive glycosides could be obtained, opening a new field for the application of these catalysts. The xylanolytic enzymes are produced in nature mainly by bacteria and fungi for degradation of plant cell wall polysaccharides. Among these organisms, filamentous fungi are the ones which have aroused the greatest interest as producers of these enzymes. The reasons are the higher levels of xylanolytic activities displayed by fungi and the frequent secretion of the desired enzymes to the extracellular medium, which facilitates both the purification and direct use of fungal crudes for several applications...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Bioquímica y Biología Molecular, leída el 02-06-2017