Precursors of ricin and Ricinus communis agglutinin. Glycosylation and processing during synthesis and intracellular transport

Eur J Biochem. 1985 Jan 15;146(2):411-6. doi: 10.1111/j.1432-1033.1985.tb08667.x.

Abstract

During synthesis in vivo the castor bean lectin precursors initially appear in the endoplasmic reticulum as a group of core glycosylated polypeptides of relative molecular mass 64 000-68 000. Pretreatment of intact castor bean endosperm tissue with tunicamycin partially inhibits the cotranslational core glycosylation step and results in the accumulation of a single sized unglycosylated precursor polypeptide of relative molecular mass 59 000. The glycosylated precursors in the endoplasmic reticulum were enzymically converted to the 59 000-Mr form by incubation with endoglucosaminidase H. Intracellular transport of the glycosylated lectin precursors from the endoplasmic reticulum to a denser vesicle fraction was accompanied by modifications to the oligosaccharide moieties which conferred resistance to the action of endoglucosaminidase H. The post-translational addition of fucose to the carbohydrate chain was identified as one of the oligosaccharide modification steps. Fucose addition was catalysed by a glycosyltransferase associated with a smooth-surfaced membrane fraction which was distinct from the endoplasmic reticulum and which was tentatively identified as the Golgi apparatus. Glycosylation was not essential for intracellular transport of the lectin precursors: unglycosylated precursor synthesized in the presence of tunicamycin gave rise to unglycosylated lectin subunits in the protein bodies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agglutination Tests
  • Biological Transport
  • Castor Bean
  • Endoplasmic Reticulum / metabolism
  • Golgi Apparatus / metabolism
  • Intracellular Membranes / metabolism
  • Peptides / metabolism
  • Plant Lectins
  • Plants, Toxic
  • Protein Precursors / metabolism*
  • Ricin / isolation & purification*
  • Transcription, Genetic / drug effects
  • Tunicamycin / pharmacology

Substances

  • Peptides
  • Plant Lectins
  • Protein Precursors
  • Tunicamycin
  • Ricin