Fig. 5

Crystallographic structure of XacAbf51 reveals a typical fold of GH51 arabinofuranosidases and a disulfide bridge at − 1 subsite conserved in TxAbfD3, but divergent in other structurally characterized GH51 enzymes. a Scheme of XacAbf51 domain architecture (top) and cartoon representation of the 3D structure (bottom) highlighting the distance (3.7 Å) between the catalytic residues (sticks) compatible with the retaining mechanism of hydrolysis found in GH51 family. b Magnified view of − 1 subsite (ball and sticks, light gray C atoms) in which a glycerol molecule (yellow C atoms) is bound mimicking part of the arabinose scaffold observed in the crystallographic structure of TmAbf51–arabinose complex (pink C atoms). c Structure-based sequence alignment of − 1 subsite (boxed residues) from the GH51 enzymes of known structure. Dark violet represents identical residues, light violet semi-conserved and yellow highlights the cysteine residues that form a disulfide bridge only in the XacAbf51 and TxAbfD3 enzymes of the presented comparison. Tm: Thermotoga maritima; Tp: Thermotoga petrophila; Bl: Bifidobacterium longum; Rt: Ruminiclostridium thermocellum; Gs: Geobacillus stearothermophilus