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Fig. 9 | Biotechnology for Biofuels

Fig. 9

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

Fig. 9

Molecular diversity of arabinoxylan-degrading mechanisms by Abfs. a The active site of Araf62A (GH62) is composed by a cleft that accommodates the xylan backbone and a − 1 subsite that binds specifically to mono-substitutions of Araf (O2- or O3-linked). The arabinose (green C atoms) and protein surface are from PDB 3WN0, while the xylan backbone (orange C atoms) is from PDB 3WN2 [42]. NR non-reducing end, R reducing end. b HiAXH-d3 from Humicola insolens (GH43) cleaves specifically the O3 linked Araf substitution from di-substituted Xylp units and displays an auxiliary pocket to accommodate the di-substitution. The residues W526 selects a single orientation for arabinoxylan binding into the active site via solvent-mediated interactions (dashed lines) with the endocyclic oxygen of +2R Xylp (PDB 3ZXK, [14]). c The active site of XacAbf51 also has an auxiliary pocket to accommodate di-substitutions, but the positioning of W254 seems to accept the binding of arabinoxylan in the direct and reverse direction to allow the cleavage of O3 and O2 substitutions, respectively, making this enzyme a generalist Abf

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