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The mechanism by which a distinguishing arabinofuranosidase can cope with internal di-substitutions in arabinoxylans

dos Santos, Camila Ramos, de Giuseppe, Priscila Oliveira, de Souza, Flávio Henrique Moreira, Zanphorlin, Letícia Maria, Domingues, Mariane Noronha, Pirolla, Renan Augusto Siqueira, Honorato, Rodrigo Vargas, Tonoli, Celisa Caldana Costa, de Morais, Mariana Abrahão Bueno, de Matos Martins, Vanesa Peixoto, Fonseca, Lucas Miranda, Büchli, Fernanda, de Oliveira, Paulo Sergio Lopes, Gozzo, Fábio Cesar, Murakami, Mário Tyago
Biotechnology for biofuels 2018 v.11 no.1 pp. 223
alpha-N-arabinofuranosidase, arabinoxylan, biomass, cell walls, corn stover, crystal structure, depolymerization, fungi, grasses, hydrolysis, mass spectrometry, reducing sugars, saccharification, sugarcane, sugarcane bagasse, xylan
BACKGROUND: Arabinoxylan is an abundant polysaccharide in industrially relevant biomasses such as sugarcane, corn stover and grasses. However, the arabinofuranosyl di-substitutions that decorate the xylan backbone are recalcitrant to most known arabinofuranosidases (Abfs). RESULTS: In this work, we identified a novel GH51 Abf (XacAbf51) that forms trimers in solution and can cope efficiently with both mono- and di-substitutions at terminal or internal xylopyranosyl units of arabinoxylan. Using mass spectrometry, the kinetic parameters of the hydrolysis of 3³-α-L-arabinofuranosyl-xylotetraose and 2³,3³-di-α-L-arabinofuranosyl-xylotetraose by XacAbf51 were determined, demonstrating the capacity of this enzyme to cleave arabinofuranosyl linkages of internal mono- and di-substituted xylopyranosyl units. Complementation studies of fungal enzyme cocktails with XacAbf51 revealed an increase of up to 20% in the release of reducing sugars from pretreated sugarcane bagasse, showing the biotechnological potential of a generalist GH51 in biomass saccharification. To elucidate the structural basis for the recognition of internal di-substitutions, the crystal structure of XacAbf51 was determined unveiling the existence of a pocket strategically arranged near to the − 1 subsite that can accommodate a second arabinofuranosyl decoration, a feature not described for any other GH51 Abf structurally characterized so far. CONCLUSIONS: In summary, this study reports the first kinetic characterization of internal di-substitution release by a GH51 Abf, provides the structural basis for this activity and reveals a promising candidate for industrial processes involving plant cell wall depolymerization.