title: Identification of a novel functional domain of ricin responsible for its potent toxicity.
abstract: Ribosome-inactivating proteins (RIPs) are toxic N-glycosidases that depurinate the universally conserved α-sarcin loop of large rRNAs. They have received attention in biological and biomedical research because of their unique biological activities toward animals and human cells as cell-killing agents. A better understanding of the depurination mechanism of RIPs could allow us to develop potent neutralizing antibodies and to design efficient immunotoxins for clinical use. Among these RIPs, ricin exhibited remarkable efficacy in depurination activity and highly conserved tertiary structure with other RIPs. It can be considered as a prototype to investigate the depurination mechanism of RIPs. In the present study, we successfully identified a novel functional domain responsible for controlling the depurination activity of ricin, which is located far from the enzymatic active site reported previously. Our study indicated that ricin A-chain mAbs binding to this domain (an α-helix comprising the residues 99-106) exhibited an unusual potent neutralizing ability against ricin in vivo. To further investigate the potential role of the α-helix in regulating the catalytic activity of ricin, ricin A-chain variants with different flexibility of the α-helix were rationally designed. Our data clearly demonstrated that the flexibility of the α-helix is responsible for controlling the depurination activity of ricin and determining the extent of protein synthesis inhibition, suggesting that the conserved α-helix might be considered as a potential target for the prevention and treatment of RIP poisoning.
authors.affiliation: International Joint Cancer Institute, The Second Military Medical University, Shanghai 200433, China.
authors.forename: Jianxing
authors.initials: J
authors.lastname: Dai
authors.forename: Lei
authors.initials: L
authors.lastname: Zhao
authors.forename: Haiou
authors.initials: H
authors.lastname: Yang
authors.forename: Huaizu
authors.initials: H
authors.lastname: Guo
authors.forename: Kexing
authors.initials: K
authors.lastname: Fan
authors.forename: Huaqing
authors.initials: H
authors.lastname: Wang
authors.forename: Weizhu
authors.initials: W
authors.lastname: Qian
authors.forename: Dapeng
authors.initials: D
authors.lastname: Zhang
authors.forename: Bohua
authors.initials: B
authors.lastname: Li
authors.forename: Hao
authors.initials: H
authors.lastname: Wang
authors.forename: Yajun
authors.initials: Y
authors.lastname: Guo
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002474:Cell-Free System; D002522:Chlorocebus aethiops; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000276:immunology; D056004:Molecular Dynamics Simulation; D012335:RNA, Ribosomal / Q000378:metabolism; D012276:Ricin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014709:Vero Cells
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D012335:RNA, Ribosomal; D012276:Ricin