<p>This group represents a subfamily of the haloacid dehalogenase superfamily of aspartate-nucleophile hydrolases. Subfamily IA, B, C and D are distinguished from the rest of the superfamily by the presence of a variable domain between the first and second conserved catalytic motifs. In subfamilies IA and IB, this domain consists of an alpha-helical bundle. It was necessary to model these two subfamilies separately, breaking them at an apparent phylogenetic bifurcation, so that the resulting model(s) are not so broadly defined that members of subfamily III (which lack the variable domain) are included. </p>