MOLECULAR EVOLUTION OF HYDANTOINASES

The complete amino acid sequence of the hydantoinase from Arthrobacter aurescens DSM 3745 has been derived by automated Edman degradation. T his is the fi rst ever reported amino acid sequence of a non-ATP-depen dent hydantoinase, which hydrolyzes 5'-monosubstituted hydantoin deriv atives L-selectively, A homology search performed in protein and nucle ic acid databases retrieved only distantly related proteins. All of th ese are members of the recently described protein superfamily of amido hydrolases related to ureases (Holm and Sander, Proteins 28: 72-82, 19 97). Phylogenetic analysis revealed that the novel hydantoinase forms a new branch separate from other hydantoin cleaving enzymes like dihyd ropyrimidinases (EC 3.5.2.2) and allantoinases (EC 3,5,2.5), Our resul ts suggests that the enzymes of this protein superfamily have evolved from a common ancestor and therefore are the product of divergent evol ution, We show further that the enclosed gene families developed very early in evolution, probably prior to the formation of the three domai ns, Archaea, Eukarya and Bacteria, Hydantoinases related to ATP-depden t N-methylhydantoinases (EC 3.5.2.14) or 5-oxoprolinases (EC 3.5.2.9) do not belong to this superfamily.