<p>The haloacid dehydrogenase (HAD) superfamily includes phosphatases, phosphonatases, P-type ATPases, beta-phosphoglucomutases, phosphomannomutases, and dehalogenases, which are involved in a variety of cellular processes ranging from amino acid biosynthesis to detoxification [<cite idref="PUB00003337"/>].</p><p>Crystal structures of proteins from the HAD superfamily show that these proteins all share a conserved alpha/beta-domain classified as a hydrolase fold, which is similar to the Rossmann fold [<cite idref="PUB00026943"/>]. This conserved domain usually contains an insertion domain. The insertion domain shows structural variation among the different functional classes of the haloacid dehalogenase superfamily.</p><p>This entry represents a Rossmann fold insertion domain found in some HAD members, including 4-nitrophenylphosphatase. </p>