Primary Sequence and Three-Dimensional Structural Comparison between Malanin and Ricin, a Type II Ribosome-Inactivating Protein.

Malanin is a new type II ribosome-inactivating protein (RIP) purified from Malania oleifera, a rare, endangered tree is only found in the southwest of Guangxi Province and the southeast of Yunnan Province, China. The gene coding sequence of malanin was found from the cDNA library of M. oleifera seeds by employing the ten N-terminal amino acid sequences of malanin, DYPKLTFTTS for chain-A and DETXTDEEFN (X was commonly C) for chain-B. The results showed a 65% amino acid sequence homology between malanin and ricin by DNAMAN 9.0 software, the active sites of the two proteins were consistent, and the four disulfide bonds were in the same positions. The primary sequence and three-dimensional structures of malanin and ricin are likely to be very similar. Our studies suggest that the mechanism of action of malanin is expected to be analogous to ricin, indicating that it is a member of the type II ribosome-inactivating proteins. This result lays the foundation for further study of the anti-tumor activities of malanin, and for the application of malanin as a therapeutic agent against cancers.