Ricin B chain-containing immunotoxins prepared with heat-denatured B chain lacking galactose-binding ability potentiate the cytotoxicity of a cell-reactive ricin A chain immunotoxin

Edward J. Wawrzynczak, Alex F. Drake, Graham J. Watson, Philip E. Thorpe, Ellen S. Vitetta

Research output: Contribution to journalArticle

15 Scopus citations

Abstract

Ricin B chain incubated at 37°C in the absence of lactose loses its ability to bind the galactose-containing protein, asialofetuin. Circular dichroism analysis of the B chain thermal denaturation indicates that the loss of galactose-binding ability by the B chain correlates with limited unfolding of the molecule. As a result of this conformational change, disulfide bonds that are shielded from the solvent by the compact folded structure of the B chain become exposed and the chitobiosyl cores of both N-linked oligomannose chains become susceptible to cleavage by endoglycosidases. The heat-denatured B chain does not enhance the toxicity of a ricin A chain-containing rabbit anti-human immunoglobulin (RAHIg-A) to Daudi cells. However, when heat-denatured B chain is coupled to goat anti-rabbit immunoglobulin (GARIg), the resulting immunotoxin, GARIg-hdB, potentiates the killing of RAHIg-A-treated Daudi cells to an extent similar to that of an immunotoxin prepared with GARIg and native B chain. These results indicate that the native, galactose-binding structure of the B chain is not necessary to enhance the cytotoxicity of the cell-reactive A chain immunotoxin (IT-A) and suggests that regions of the B chain exposed by unfolding the molecule may mediate potentiation of cytotoxicity.

Original languageEnglish (US)
Pages (from-to)55-62
Number of pages8
JournalBBA - Molecular Cell Research
Volume971
Issue number1
DOIs
StatePublished - Aug 19 1988

Keywords

  • Galactose binding
  • Immunotoxin
  • Ricin B chain

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology

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