The effect of substitutions on human β-mannosidase structure. a . R182W , b . G392E , c . S505P and d . R641H. Sections where the substitutions occur on the WT and mutant human β-mannosidase structures are shown. The WT and mutated residues are shown in red and green, respectively. The residues affected by substitutions are coloured turquoise. All amino acids involved in the mutations and/or affected by the substitutions are in stick representation, while the segments of the protein backbone are shown in ribbon representations (light grey). The dotted lines signify the interactions between the amino acid residues.