title: Signal peptide-regulated toxicity of a plant ribosome-inactivating protein during cell stress.
abstract: The fate of the type I ribosome-inactivating protein (RIP) saporin when initially targeted to the endoplasmic reticulum (ER) in tobacco protoplasts has been examined. We find that saporin expression causes a marked decrease in protein synthesis, indicating that a fraction of the toxin reaches the cytosol and inactivates tobacco ribosomes. We determined that saporin is largely secreted but some is retained intracellularly, most likely in a vacuolar compartment, thus behaving very differently from the prototype RIP ricin A chain. We also find that the signal peptide can interfere with the catalytic activity of saporin when the protein fails to be targeted to the ER membrane, and that saporin toxicity undergoes signal sequence-specific regulation when the host cell is subjected to ER stress. Replacement of the saporin signal peptide with that of the ER chaperone BiP reduces saporin toxicity and makes it independent of cell stress. We propose that this stress-induced toxicity may have a role in pathogen defence.
authors.affiliation: Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle Ricerche, Via Bassini 15, 20133 Milano, Italy.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Marshall
authors.forename: Francesca
authors.initials: F
authors.lastname: D'Avila
authors.forename: Alessandra
authors.initials: A
authors.lastname: Di Cola
authors.forename: Roberta
authors.initials: R
authors.lastname: Traini
authors.forename: Laura
authors.initials: L
authors.lastname: Spanò
authors.forename: Maria Serena
authors.initials: MS
authors.lastname: Fabbrini
authors.forename: Aldo
authors.initials: A
authors.lastname: Ceriotti
mesh_terms: D000595:Amino Acid Sequence; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D006031:Glycosylation; D042541:Intracellular Space / Q000378:metabolism; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms; D021382:Protein Sorting Signals / Q000235:genetics / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000378:metabolism / Q000633:toxicity; D021381:Protein Transport; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D054789:Ribosome Inactivating Proteins, Type 1 / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*; D029750:Saponaria / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D000076985:Saporins; D013312:Stress, Physiological; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism
chemical_list: D018832:Molecular Chaperones; D010940:Plant Proteins; D020033:Protein Isoforms; D021382:Protein Sorting Signals; D011500:Protein Synthesis Inhibitors; D011993:Recombinant Fusion Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D000076985:Saporins