Lectin-deficient ricin toxin indicates cells bearing the D-mannose receptor

Arthur E. Frankel, Tao Fu, Christopher Burbage, Edward Tagge, Billie Harris, Joseph Vesely, Mark C. Willingham

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Ricin toxin with genetic or chemical modification of lectin sites has been previously reported to show markedly reduced cytotoxicity to cells following uptake by several receptors including the mannose receptor. Investigators have hypothesized that an intracellular galactoside-binding function was required for optimal intracellular targeting of ricin for these receptors. We have prepared insect-derived mutant ricin toxin B chain (RTB) with modifications of three lectin site domains (1α, 1β, and 2γ) yielding a 1000-fold reduced galactoside avidity. After reassociation with plant RTA, the recombinant heterpdimer and plant ricin were tested for cytotoxicity on mammalian cells expressing (mouse peritoneal macrophages, J774E cells, and MMR61 cells) or not expressing (KB cells) the D-mannose receptor. Receptor expression was confirmed by immunofluorescence microscopy. Lactose was included in the media to block cell-surface galactoside binding, and mannan was added as a control in each experiment to confirm mannose receptor-specific targeting. Plant ricin A chain (RTA) and E. coli-derived RTA were also tested for cytotoxicity on J774E and KB cells. Both wild-type and lectin-deficient ricin displayed mannose-receptor mediated cell cytotoxicity. This is the first report of a genetically modified ricin showing that RTB intracellular galactose binding activity is not required for ricin cytotoxicity. Sensitivity of mannose-receptor bearing cells, but not control cells, to mannosylated RTA, but not unglycosylated RTA, confirmed these observations. These results imply fusion toxins employing ricin can be prepared with maximal reductions in normal tissue binding.

Original languageEnglish (US)
Pages (from-to)251-258
Number of pages8
JournalCarbohydrate Research
Issue number3
StatePublished - May 16 1997


  • Mannose receptor
  • Ricin

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry
  • Organic Chemistry


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