Truncations of gelonin lead to a reduction in its cytotoxicity

Gelonin is a single chain ribosome-inactivating protein (RIP) with potential applications as a bullet of immunoconjugate for the treatment of cancer and AIDS. Using truncated forms of gelonin, we now report the relationship between its conformation and function. Circular dichroism (CD) and fluorescence spectra show that the N-terminus forms beta-sheets whereas the C-terminus contains alpha-helices of secondary structures. Biological experiments indicate that all gelonin truncation mutants lose partial toxicity compared to intact gelonin, an effect most strongly seen with C-terminally truncated gelonin. Similar evidence is also provided using a DNase-like activity assay. In addition, the intact gelonin exhibits the highest cytotoxicity to cancer cells. These results suggest that truncations of the terminal region of gelonin negatively regulate its function dominantly and that, due to its toxicity, intact gelonin is an important potential immunoconjugate.