Plant chitinases use two different hydrolytic mechanisms

Bacterial, fungal, animal, and some plant chitinases form family 18 of glycosyl hydrolases. Most plant chitinases form the family 19. While some chitinases also have lysozyme activity, animal lysozymes belong to different families. For glycosyl hydrolases, two reaction mechanisms are possible, leading to either retention or inversion of the anomeric configuration. We analyzed by HPLC the stereochemical outcome of the hydrolysis catalyzed by cucumber and bean chitinases, belonging to families 18 and 19, respectively. Cucumber chitinase used the retaining mechanism as known for bacterial chitinases and hen egg white lysozyme for which the mechanism has been determined. In contrast, bean chitinase catalyzed the hydrolysis of chitooligosaccharides with overall inversion of anomeric configuration.