Free Ricin A Chain, Proricin, and Native Toxin Have Different Cellular Fates When Expressed in Tobacco Protoplasts

• DOI: 10.1074/jbc.273.23.14194
• Publication Date: 2002-07-26T14:47:21Z
• Authors: Lorenzo Frigerio; Alessandro Vitale; J. Michael Lord; Aldo Ceriotti; Lynne M. Roberts
• Keywords: Ricin; Protoplast

The catalytic A subunit of ricin can inactivate eukaryotic ribosomes, including those Ricinus communis where the toxin is naturally produced. How such plant cells avoid intoxication has remained an open question. Here we report transient expression a number chain-encoding cDNA constructs in tobacco protoplasts. Ricin chain entered endoplasmic reticulum lumen, it was efficiently glycosylated, but toxic to and disappeared with time brefeldin A-insensitive manner, suggesting reverse translocation cytosol eventual degradation. Proricin (the natural precursor form containing B chains joined together by linker sequence) transported vacuole, processed its mature form, not toxic. Free proricin were secreted, whereas free found entirely extracellular medium. coexpression resulted formation disulfide-linked, transport-competent heterodimers, which concomitant reduction observed cytotoxicity. These results suggest that production as essential for routing vacuole protection ricin-producing cells.