Abstract
The sequence of narbonin, a leguminous seed protein with the TIM barrel structure but of unknown function, is significantly similar to endo-β-N-acetylglucosaminidase H from Streptomyces plicatus. This protein is a member of a family of chitinases, ‘Family 18’ of the glycosyl hydrolases. It is proposed that the catalytic domain of this family has the TIM barrel structure. It is proposed that narbonin has chitinase activity, or has been derived from a chitinase by loss of function.