Purification of a new ribosome-inactivating protein from the seeds of Cinnamomum porrectum and characterization of the RNA N-glycosidase activity of the toxic protein
1996
Li, X.D. | Liu, W.Y. | Niu, C.I.
Porrectin, a new type II ribosome-inactivating protein (RIP), was purified from the seeds of the camphor tree (Cinnamomum porrectum) by affinity chromatography on acid-treated Sepharose 4B. Porrectin is a glycoprotein (Mr 64500, sugar content 2.5%) consisting of an A-chain (Mr 30500) and a B-chain (Mr 33500) linked by the disulfide bond. The terminal sugar of glycan in porrectin B-chain is determined to be mannose. By non-denaturing polyacrylamide gel electrophoresis, porrectin displayed three isoforms that have different pI values with the same molecular weight. Porrectin is a potent inhibitor of eukaryotic protein synthesis in the rabbit reticulocyte lysate system. The molecular mechanism of action of porrectin on rat liver ribosomes is demonstrated to be specific for RNA N-glycosidase. The cleavage site is the adenosine at position 4324 (rat liver 28S rRNA) embedded in the highly conserved ricin/alpha-sarcin ('R/S') domain.
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