InterPro: IPR010025 HAD-superfamily phosphatase, subfamily IIIB, AphA

This family of proteins is a member of the IIIB subfamily (IPR001001) of the haloacid dehalogenase (HAD) superfamily of hydrolases. All characterised members of subfamily III and most characterised members of the HAD superfamily are phosphatases. HAD superfamily phosphatases contain active site residues in several conserved catalytic motifs [1], all of which are found conserved in this family.

AphA is a periplasmic acid phosphatase of Escherichia coli [2] belonging to class B bacterial phosphatases [3], which is part of the DDDD superfamily of phosphohydrolases. The crystal structure of AphA has been determined at 2.2A and its resolution extended to 1.7A. Despite the lack of sequence homology, the AphA structure reveals a haloacid dehalogenase-like fold. This finding suggests that this fold could be conserved among members of the DDDD superfamily of phosphohydrolases. The active enzyme is a homotetramer built by using an extended N-terminal arm intertwining the four monomers. The active site of the native enzyme hosts a magnesium ion, which can be replaced by other metal ions. The structure explains the non-specific behaviour of AphA towards substrates, while a structure-based alignment with other phosphatases provides clues about the catalytic mechanism [4].