2.8-A crystal structure of a nontoxic type-II ribosome-inactivating protein, ebulin l.
Ebulin l 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 disulfide-linked heterodimer composed of a toxic A chain and a galactoside-specific lectin B chain. A normal level of ribosome-inactivating N-glycosidase activity, characteristic of the A chain of type-II RIP, has been demonstrated for ebulin l. However, ebulin is considered a nontoxic type-II RIP due to a reduced cytotoxicity on whole cells and animals as compared with other toxic type-II RIP like ricin. The molecular cloning, amino acid sequence, and the crystal structure of ebulin l are presented and compared with ricin. Ebulin l is shown to bind an A-chain substrate analogue, pteroic acid, in the same manner as ricin. The galactoside-binding ability of ebulin l is demonstrated crystallographically with a complex of the B chain with galactose and with lactose. The negligible cytotoxicity of ebulin l is apparently due to a reduced affinity for galactosides. An altered mode of galactoside binding in the 2gamma subdomain of the lectin B chain primarily causes the reduced affinity.
Pascal
J M
JM
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
Day
P J
PJ
Monzingo
A F
AF
Ernst
S R
SR
Robertus
J D
JD
Iglesias
R
R
Pérez
Y
Y
Férreras
J M
JM
Citores
L
L
Girbés
T
T
D000595:Amino Acid Sequence; D001483:Base Sequence; D003460:Crystallization; D018360:Crystallography, X-Ray; D018744:DNA, Plant; D005690:Galactose / Q000737:chemistry; D007785:Lactose / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009699:N-Glycosyl Hydrolases; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D017510:Protein Folding; D017433:Protein Structure, Secondary; D054790:Ribosome Inactivating Proteins, Type 2
D018744:DNA, Plant; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D009699:N-Glycosyl Hydrolases; D007785:Lactose; D005690:Galactose