PRIMARY STRUCTURE AND MOLECULAR MODELING OF MISTLETOE LECTIN-I FROM VISCUM-ALBUM

The first three-dimensional structure of the ribosome inactivating pro tein mistletoe lectin I (ML-I) hom Viscum album has been modeled on th e basis of the X-ray structure of castor bean ricin from Ricinus commu nis. The relative high sequence homology and conserved secondary struc ture enabled accurate modeling. The 196 sequence changes between ML-I and ricin could be accomodated with only little pertubation in the mai n chain folding. A close comparison of the primary structures of ML-I and ricin is given and the effects of the sequence changes are elucida ted on the basis of the modeled three-dimensional structure. Differenc es have been identified in the vicinity of the active site, in the hig h affinity galactose binding site and in the interface between the A a nd B chains, which might account for the reduced cytotoxicity of ML-I. (C) 1998 Academic Press.