Taxon-specific lens crystallins with endogenous enzymic activities: some perspectives on synthetic applications

A systematic and general approach has been carried out to provide basic structural and mechanistic information on epsilon- and delta-crystallin with lactate dehydrogenase and argininosuccinate lyase activities respectively from representative species of birds. A detailed kinetic analysis of these two crystallins revealed considerable differences in the enzymic activities among different species of birds. Especially noteworthy is the abundant presence of high activity in duck and goose epsilon- and delta-crystallins in contrast with the total lack of epsilon-crystallin and diminished activities of delta-crystallins in chicken and pigeon lenses. Sequence comparison of inactive pigeon delta-crystallin and active duck crystallin revealed several sequence variations and replacements which may account for the loss of argininosuccinate lyase activity in the lenses of certain birds. Bio-organic synthesis based on epsilon- and delta-crystallins isolated from duck lenses provides an efficient and practical tool for asymmetric or enantioselective synthesis of some pharmaceutically important chiral intermediates which may open new avenues and potentials in crystallin research.