2.8-angstrom crystal structure of a nontoxic type-II ribosome-inactivatingprotein, ebulin 1

Ebulin 1 is a type-II ribosome-inactivating protein (RIP) isolated from the leaves of Sambucus ebulus L, As with other type-II RIP, ebulin is a disulf ide-linked heterodimer composed of a toxic A chain and a galactoside-specif ic lectin B chain, A normal level of ribosome-inactivating N-glycosidase ac tivity, characteristic of the A chain of type-II RIP, has been demonstrated for ebulin 1, However, ebulin is considered a nontoxic type-II RIP due to a reduced cytotoxicity on whole cells and animals as compared with other to xic type-II RIP like ricin, The molecular cloning, amino acid sequence, and the crystal structure of ebulin 1 are presented and compared with ricin, E bulin 1 is shown to bind an A-chain substrate analogue, pteroic acid, in th e same manner as ricin, The galactoside-binding ability of ebulin 1 is demo nstrated crystallographically with a complex of the B chain with galactose and with lactose, The negligible cytotoxicity of ebulin 1 is apparently due to a reduced affinity for galactosides. An altered mode of galactoside bin ding in the 2 gamma subdomain of the lectin B chain primarily causes the re duced affinity. (C) 2001 Wiley-Liss, Inc.