Exploring the Molecular Basis for Substrate Affinity and Structural Stability in Bacterial GH39 β-Xylosidases.

The glycoside hydrolase family 39 (GH39) is a functionally expanding family with limited understanding about the molecular basis for substrate specificity and extremophilicity. In this work, we demonstrate the key role of the positive-subsite region in modulating substrate affinity and how the lack of a C-terminal extension impacts on oligomerization and structural stability of some GH39 members. The crystallographic and SAXS structures of a new GH39 member from the phytopathogen support the importance of an extended C-terminal to promote oligomerization as a molecular strategy to enhance thermal stability.

N-glycan Utilization by Bifidobacterium Gut Symbionts Involves a Specialist β-Mannosidase.

Bifidobacteria represent one of the first colonizers of human gut microbiota, providing to this ecosystem better health and nutrition. To maintain a mutualistic relationship, they have enzymes to degrade and use complex carbohydrates non-digestible by their hosts. To succeed in the densely populated gut environment, they evolved molecular strategies that remain poorly understood.

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

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 (Abf51) that forms trimers in solution and can cope efficiently with both mono- and di-substitutions at terminal or internal xylopyranosyl units of arabinoxylan.

Structural basis of exo-β-mannanase activity in the GH2 family.

The classical microbial strategy for depolymerization of β-mannan polysaccharides involves the synergistic action of at least two enzymes, endo-1,4-β-mannanases and β-mannosidases. In this work, we describe the first exo-β-mannanase from the GH2 family, isolated from pv. (XacMan2A), which can efficiently hydrolyze both manno-oligosaccharides and β-mannan into mannose.

Unraveling the genetic basis of xylose consumption in engineered Saccharomyces cerevisiae strains.

The development of biocatalysts capable of fermenting xylose, a five-carbon sugar abundant in lignocellulosic biomass, is a key step to achieve a viable production of second-generation ethanol. In this work, a robust industrial strain of Saccharomyces cerevisiae was modified by the addition of essential genes for pentose metabolism. Subsequently, taken through cycles of adaptive evolution with selection for optimal xylose utilization, strains could efficiently convert xylose to ethanol with a yield of about 0.