(a) Superposition of the A domain (red) and B domain (blue) of LdtMt2. The major differences in the core fold (indicated by >) are the α-helix (residues 180–187) inserted between β-strands β2 and β3, which is not present in the A domain, and the longer loop connecting β6 and β7 in the B domain. (b) Superposition of domain A (red) from LdtMt2 with the homologous domain of the endo-β-1,4-mannanase from C. fimi (light blue; PDB entry 2x2y
). Conserved residues of LdtMt2 are shown as yellow stick models. Five threonine side chains on the surface of the three-stranded β-sheet show a similar pattern in the mannanase and the A domain of LtdMt2 and are shown as blue sticks.