Structural investigation of the sweet-tasting proteins thaumatin and monellin by immunological studies

Abstract

Rabbit antibodies were produced against thaumatin I, a sweet-tasting protein from plant origin using the technique of double diffusion in agar. Cross-reactions were observed between these antibodies and thaumatin I, monellin and chemically modified thaumatins. No cross-reaction was observed between the antibodies of thaumatin I and the not sweet-tasting iodinated monellin. This lack of cross-reaction may be due to the fact that iodination splits monellin into its A and B chain, resulting in a disturbance of the tertiary structure of the molecule. The appearance of precipitation lines from thaumatin I as well as from monellin in reaction with the antibodies of thaumatin in the immunodiffusion assay indicates that thaumatin and monellin are immunologically closely related. An identical conformational antigenic determinant in both molecules is probably responsible for this relationship. It is tentatively concluded that the identical conformational determinant coincides with the active site responsible for the sweet-taste sensation.