Evolutionary relationship and application of a superfamily of cyclic amidohydrolase enzymes

Cyclic amidohydrolases belong to a superfamily of enzymes that catalyze the hydrolysis of cyclic C-N bonds. They are commonly found in nucleotide metabolism of purine and pyrimidine. These enzymes share similar catalytic mechanisms and show considerable structural homologies, suggesting that they might have evolved from a common ancestral protein. Homology searches based on common mechanistic properties and three-dimensional protein structures provide clues to the evolutionary relationships of these enzymes. Among the superfamily of enzymes, hydantoinase has been highlighted by its potential for biotechnological applications in the production of unnatural amino acids. The enzymatic process for the production of optically pure amino acids consists of three enzyme steps: hydantoin racemase, hydantoinase, and N-carbamoylase. For efficient industrial application, some critical catalytic properties such as thermostability, catalytic activity, enantioselectivity, and substrate specificity require further improvement. To this end, isolation of new enzymes with desirable properties from natural sources and the optimization of enzymatic processes were attempted. A combination of directed evolution techniques and rational design approaches has made brilliant progress in the redesign of industrially important catalytic enzymes; this approach is likely to be widely applied to the creation of designer enzymes with desirable catalytic properties.