Cinphorin: a novel type II ribosome-inactivating protein with miniature active A-chain

Cinnamomin is a type II ribosome-inactivating protein (RIP) isolated from the seed of camphor tree (Cinnamomum camphora). Recently, a small RIP named as cinphorin was isolated from the seed of camphor tree. The reduced cinphorin exhibited the RNA N-glycosidase activity and inhibitory activity to protein synthesis in vitro like the reduced cinnamomin did. Cinphorin B-chain exhibited the same N-terminal 10 amino acid sequence and molecular mass as the B-chain of cinnamomin. Its A-chain exhibited the same 10 N-terminal amino acid sequence and owned a C-terminal cysteine residue linked to the B-chain, but the molecular mass of cinphorin A-chain was only half of cinnamomin A-chain. RT-PCR and Northern blotting revealed that there was no corresponding mRNA of cinphorin. Cinphorin is probably produced from cinnamomin by protein splicing.