Cation channel formed at lipid bilayer by Cinnamomin, a new type II ribosome-inactivating protein

Screening and characterization of inhibitory vNAR targeting nanodisc-assembled influenza M2 proteins

Influenza A virus poses a constant challenge to human health. The highly conserved influenza matrix-2 (M2) protein is an attractive target for the development of a universal antibody-based drug. However, screening using antigens with subphysiological conformation in a nonmembrane environment significantly reduces the generation of efficient antibodies. Here, M2(1-46) was incorporated into nanodiscs (M2-nanodiscs) with M2 in a membrane-embedded tetrameric conformation, closely resembling its natural physiological state in the influenza viral envelope. M2-nanodisc generation, an antigen, was followed by Chiloscyllium plagiosum immunization. The functional vNARs were selected by phage display panning strategy from the shark immune library. One of the isolated vNARs, AM2H10, could specifically bind to tetrameric M2 instead of monomeric M2e (the ectodomain of M2 protein). Furthermore, AM2H10 blocked ion influx through amantadine-sensitive and resistant M2 channels. Our findings indicated the possibility of developing functional shark nanobodies against various influenza viruses by targeting the M2 protein.

Cinnamomin: a multifunctional type II ribosome-inactivating protein

Plant ribosome-inactivating proteins (RIPs) are a group of toxic proteins that can irreversibly inactivate ribosomes by specifically removing the conserved adenine base from the "Sarcin/Ricin domain" of the 28S RNA in ribosome. Cinnamomin is a novel type II RIP isolated in our laboratory from the mature seeds of camphor tree. Besides site-specific deadenylation of the A4324 in the Sarcin/Ricin domain of rat ribosome, this protein could also release the adenine base from DNA molecules at multiple sites and from AMP, ADP, dAMP and adenosine. Furthermore, cinnamomin displays cytotoxicity to carcinoma cells and insect larvae by modifying their ribosomal RNA. These functions possessed by cinnamomin shed a new light on the possible application of cinnamomin in the field of immunotoxin design and transgenic reagents. In this review, we introduce the major recent results on cinnamomin obtained in our laboratory, including purification of this protein, characterization of its enzymatic mechanism, structure and function, gene pattern, physiological role and its biological implications in cytotoxicity.

The pH-dependent interaction of cinnamomin with lipid membranes investigated by fluorescence methods

Cinnamomin, a new type II ribosome-inactivating protein (RIP), was found to be able to induce the release of calcein loaded in lecithin small unilamellar vesicles and the fusion or aggregation of the lecithin liposomes. Such induction could be promoted severalfold by a pH 5.0 environment, a condition similar to that in endocytic vesicles. Lowering the pH from 7.5 to 5.0 evoked conformational changes of cinnamomin and unmasked its hydrophobic areas, including the exposure of 1-anilino-8-naphthalenesulfonate (1,8-ANS) binding sites of the molecule. Some tryptophan residues with affinity to acrylamide were demonstrated to participate in the lipid-protein interaction. The pH dependent fusogenicity of type II RIP might suggest its in vivo function as a fusogen to exert its cytotoxicity.