The crystal structure of saporin SO6 from Saponaria officinalis and its interaction with the ribosome

The 2.0 Angstrom resolution crystal structure of the ribosome inactivating protein saporin (isoform 6) from seeds of Saponaria officinalis is presente d. The fold typical of other plant toxins is conserved, despite some differ ences in the loop regions. The loop between strands beta 7 and beta 8 in th e C-terminal region which spans over the active site cleft appears shorter in saporin, suggesting an easier access to the substrate. Furthermore,ve in vestigated the molecular interaction between saporin and the yeast ribosome by differential chemical modifications. A contact surface inside the C-ter minal region of saporin has been identified. Structural comparison between saporin and other ribosome inactivating proteins reveals that this region i s conserved and represents a peculiar motif involved in ribosome recognitio n. (C) 2000 Federation of European Biochemical Societies.