Cytotoxicity of ribosome‐inactivating protein saporin is not mediated through α 2 ‐macroglobulin receptor

Saporin is a single chain ribosome‐inactivating protein produced by the plant Saponaria officinalis . Several isoforms of saporin have been isolated from various parts of the plant. In the present study recombinant saporin isoforms 5 and 6 were produced in Escherichia coli . Saporin‐6 was found to be more active than saporin‐5 in its N‐glycosidase, cytotoxic, and genomic DNA fragmentation activities. Earlier, saporin has been shown to bind low‐density lipoprotein receptor‐related protein (LRP), however, in this study the sensitivities of LRP‐negative and LRP‐positive cell lines were found to be similar towards saporin‐6 toxicity suggesting the internalization of saporin not to be solely dependent on the expression of LRP on eukaryotic cells.