ABSTRACT
The amidohydrolase superfamily is a related group of enzymes that catalyze the hydrolysis of bonds to carbonyl and phosphoryl centers. The most prominent members of this family of proteins include urease (URE), phosphotriesterase (PTE), adenosine deaminase (ADA), dihydroorotase (DHO), and atrazine chlorohydrolase (1). The reactions catalyzed by some of these enzymes are illustrated in Sch. 1. Structurally, all of these proteins have been shown to fold into a typical (βα)8-barrel motif, although the level of overall sequence identity is rather low. The hallmark for this family of enzymes is a cluster of four histidine residues that come together in three-dimensional space to form a highly structured binding site for divalent metal ions (2-4). The most common arrangement is for a binuclear metal center, as observed in the x-ray crystal structures of URE, PTE, DHO, and the phosphotriesterase homology protein (PHP), although a mononuclear metal binding site has been observed with ADA (5). Within the binuclear metal ion clusters, there
Scheme 1 Reactions catalyzed by members of the amidohydrolase superfamily.
