Fig. 4

X-ray crystal structure of the α-1,3-(3,6-anhydro)-d-galactosidase DagB. a Secondary structure representation of DagB (ZGAL_3152, GH129-like) showing the depth of the active site crevasse for ZGAL_3152 (yellow and pink secondary structure representation for each monomer, pdb id 5opq). Active site residues, colored by element, are shown in light blue for one monomer and white for the other. b Secondary structure representation showing the width of the active site crevasse. c Surface structure representation of the model orientation shown in a. d Surface structure representation of the model orientation shown in B. e Active site substructure of the α-1,3-(3,6-anhydro)-d-galactosidase ZGAL_3152 (DagB). Three putative subsites are shown as represented by bound Tris1 (subsite –1), MPD (subsite +1) and Tris2 (subsite +2). Four potential catalytically active acidic residues are shown in light blue belonging to two different monomers of ZGAL_3152. Their site-directed mutagenesis leads to inactive enzymes. The amino acids, colored by element, interact with the Tris and MDP molecules and are conserved at 80% or more within the closest DagB homologs