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Characteristics of adjacent family 6 acetylxylan esterases from Fibrobacter succinogenes and the interaction with the Xyn10E xylanase in hydrolysis of acetylated xylan

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Acetylxylan esterase genes axe6A and axe6B located adjacent to one another on a Fibrobacter succinogenes chromosome have been separately cloned and their properties characterized. The corresponding esterases contained an N-terminal carbohydrate esterase family 6 catalytic domain (CD) and a C-terminal family 6 carbohydrate-binding module (CBM). The amino acid sequences of the CDs and CBMs were found to exhibit 52% and 40% amino acid similarity, respectively. The CDs of the two esterases exhibited the highest similarity to CDs of acetylxylan esterases: AxeA from the ruminal fungi Orpinomyces sp. and BnaA from Neocallimastix patriciarum. Axe6A and Axe6B were optimally active at neutral pH and had low Km values of 0.084 and 0.056 mmol·L–1, respectively. Axe6A and Axe6B were shown to bind to insoluble cellulose and xylan and to soluble arabinoxylan. Axe6A deacetylated acetylated xylan at the same initial rate in the presence and absence of added Xyn10E xylanase from F. succinogenes, but the action of the xylanase on acetylated xylan was dependent upon the initial activity of Axe6A. The capacity of acetylxylan esterases to bind to plant cell wall polymers and to independently deacetylate xylan enabling xylanase to release xylooligo saccharides, documents the central role these enzymes have to improve access of F. succinogenes to cellulose.Key words: Fibrobacter succinogenes S85, acetylxylan esterase, xylanase, synergy.

Les acétylxylane estérases axe6A et axe6B placées l'une à côté de l'autre sur le chromosome de Fibrobacter succinogenes ont été clonées séparément et leurs propriétés furent caractérisées. Les deux estérases contenaient un domaine catalytique (DC) N-terminal de la famille 6 des estérases de glucides et un module de liaison aux glucides (MLG) C-terminal de la famille 6. Les séquences d'acides aminés des DC et MLG ont présenté 52 % et 40 % de similarité au niveau des acides aminés, respectivement. Les DC des deux estérases ont présenté un plus haut le degré de similarité aux CD des acétylxylane estérases AxeA des champignons ruminaux Orpinomyces sp. et BnA de Neocalli mastix patriciarum. Axe6A et Axe6B démontraient une activité optimale à un pH neutre et avaient des valeurs de Km basses de 0,084 et 0,056 mmol·L–1, respectivement. Il fut démontré que Axe6A et Axe6B se liaient à du cellulose et du xylane insolubles ainsi qu'à de l'arabinoxylane soluble. Axe6A a désacétylé le xylane acétylé au même taux initial en présence ou absence de la xylanase Xyn10E de F. succinogenes, mais l'action de la xylanase sur le xylane acétylé dépendait de l'activité initiale de Axe6A. La capacité des acétylxylane estérases à se lier aux polymères de parois cellulaires végétales et de désacétyler indépendamment le xylane, permettant ainsi à la xylanase de libérer les xylooligosaccharides, documente le rôle central de ses enzymes pour faciliter l'accès de F. succinogenes au cellulose.Mots clés : Fibrobacter succinogenes S85, acétylxylane estérases, xylanase, synergie.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: September 1, 2005

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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