title: The lower cytotoxicity of cinnamomin (a type II RIP) is due to its B-chain.
abstract: The cytotoxicity of intact cinnamomin (a type II ribosome-inactivating protein, RIP) and the RNA N-glycosidase activity of cinnamomin A-chain have been studied and compared with those of ricin. Cinnamomin A-chain exhibits a similar RNA N-glycosidase activity in inhibiting in vitro protein synthesis compared with that of ricin, whereas the cytotoxicity to BA/F3beta cells of intact cinnamomin is markedly lower than intact ricin. In order to demonstrate that it is the B-chains of the two RIPs that bear the difference in cytotoxicity, two hybrid RIPs are prepared from the purified A-/B-chains of cinnamomin and ricin by the disulfide exchange reaction. It has been found that hybrid RIP constructed from cinnamomin A-chain and ricin B-chain is more toxic to BA/F3beta cells than the native cinnamomin, and equivalent to the native ricin. However, the cytotoxicity to BA/F3beta cells of the hybrid RIP constructed from the ricin A-chain and cinnamomin B-chain is lower than ricin, equivalent to the native cinnamomin. Furthermore, the bound amounts of two B-chains on the cell surface are determined by the method of direct cellular ELISA and Scatchard analysis of the binding of the two B-chains indicates that cinnamomin and ricin share similar binding sites with different affinity.
authors.affiliation: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-yang Road, Shanghai 200031, China.
authors.forename: Bao-Zhong
authors.initials: BZ
authors.lastname: Wang
authors.forename: Wei-guo
authors.initials: WG
authors.lastname: Zou
authors.forename: Wang-Yi
authors.initials: WY
authors.lastname: Liu
authors.forename: Xin-yuan
authors.initials: XY
authors.lastname: Liu
mesh_terms: D001665:Binding Sites; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D009699:N-Glycosyl Hydrolases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism* / Q000633:toxicity*; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000633:toxicity*; D011869:Radioligand Assay; D054788:Ribosome Inactivating Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D012276:Ricin / Q000737:chemistry* / Q000633:toxicity
chemical_list: D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; C487938:cinnamomin protein, Cinnamonum camphora; D012276:Ricin; D009699:N-Glycosyl Hydrolases; D054788:Ribosome Inactivating Proteins