The ricinosomes of senescing plant tissue bud from the endoplasmic reticulum.
The ricinosome (synonym, precursor protease vesicle) is a novel organelle, found so far exclusively in plant cells. Electron microscopic studies suggest that it buds off from the endoplasmic reticulum in senescing tissues. Biochemical support for this unusual origin now comes from the composition of the purified organelle, which contains large amounts of a 45-kDa cysteine endoprotease precursor with a C-terminal KDEL motif and the endoplasmic reticulum lumen residents BiP (binding protein) and protein disulfide isomerase. Western blot analysis, peptide sequencing, and mass spectrometry demonstrate retention of KDEL in the protease proform. Acidification of isolated ricinosomes causes castor bean cysteine endopeptidase activation, with cleavage of the N-terminal propeptide and the C-terminal KDEL motif. We propose that ricinosomes accumulate during senescence by programmed cell death and are activated by release of protons from acidic vacuoles.
Schmid
M
M
Lehrstuhl für Botanik, Biologikum-Weihenstephan, Technische Universität München, Am Hochanger 4, D-85350 Freising, Germany.
Simpson
D J
DJ
Sarioglu
H
H
Lottspeich
F
F
Gietl
C
C
D000595:Amino Acid Sequence; D017209:Apoptosis; D015153:Blotting, Western; D002352:Carrier Proteins / Q000032:analysis; D002499:Centrifugation, Density Gradient; D003488:Cyanogen Bromide / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D022162:Cytoplasmic Vesicles / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D000091342:Endoplasmic Reticulum Chaperone BiP; D004789:Enzyme Activation; D005455:Fluorescent Antibody Technique; D006360:Heat-Shock Proteins; D006863:Hydrogen-Ion Concentration; D013058:Mass Spectrometry; D008854:Microscopy, Electron; D018832:Molecular Chaperones / Q000032:analysis; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009842:Oligopeptides / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010947:Plants, Toxic; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals; D012278:Ricinus / Q000166:cytology* / Q000254:growth & development* / Q000648:ultrastructure; D014617:Vacuoles / Q000378:metabolism
D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009842:Oligopeptides; D010446:Peptide Fragments; D011498:Protein Precursors; D021382:Protein Sorting Signals; C073762:lysyl-aspartyl-glutamyl-leucine; D003546:Cysteine Endopeptidases; D019704:Protein Disulfide-Isomerases; D003488:Cyanogen Bromide