Peptidase M55, D-aminopeptidase dipeptide-binding protein family
M55 Peptidase, D-Aminopeptidase dipeptide-binding protein (dppA; DAP dppA; EC 3.4.11.-) domain: Peptide transport systems are found in many bacterial species and generally function to accumulate intact peptides in the cell, where they are hydrolyzed. The dipeptide-binding protein (dppA) of Bacillus subtilis belongs to the dipeptide ABC transport (dpp) operon expressed early during sporulation. It is a binuclear zinc-dependent, D-specific aminopeptidase. The biologically active enzyme is a homodecamer with active sites buried in its channel. These self-compartmentalizing proteases are characterized by a SXDXEG motif. D-Ala-D-Ala and D-Ala-Gly-Gly are the preferred substrates. Bacillus subtilis dppA is thought to function as an adaptation to nutrient deficiency; hydrolysis of its substrate releases D-Ala which can be used subsequently as metabolic fuel. This family also contains a number of uncharacterized putative peptidases.