The role of CDC48 in the retro-translocation of non-ubiquitinated toxin substrates in plant cells.
When the catalytic A subunits of the castor bean toxins ricin and Ricinus communis agglutinin (denoted as RTA and RCA A, respectively) are delivered into the endoplasmic reticulum (ER) of tobacco protoplasts, they become substrates for ER-associated protein degradation (ERAD). As such, these orphan polypeptides are retro-translocated to the cytosol, where a significant proportion of each protein is degraded by proteasomes. Here we begin to characterize the ERAD pathway in plant cells, showing that retro-translocation of these lysine-deficient glycoproteins requires the ATPase activity of cytosolic CDC48. Lysine polyubiquitination is not obligatory for this step. We also show that although RCA A is found in a mannose-untrimmed form prior to its retro-translocation, a significant proportion of newly synthesized RTA cycles via the Golgi and becomes modified by downstream glycosylation enzymes. Despite these differences, both proteins are similarly retro-translocated.
Marshall
Richard S
RS
Department of Biological Sciences, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom.
Jolliffe
Nicholas A
NA
Ceriotti
Aldo
A
Snowden
Christopher J
CJ
Lord
J Michael
JM
Frigerio
Lorenzo
L
Roberts
Lynne M
LM
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D037121:Plant Lectins / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D011523:Protoplasts / Q000166:cytology / Q000378:metabolism*; D012276:Ricin / Q000378:metabolism*; D014026:Nicotiana / Q000166:cytology / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology; D000074405:Valosin Containing Protein
D018797:Cell Cycle Proteins; D037121:Plant Lectins; D010940:Plant Proteins; C017707:Ricinus communis agglutinin-1; D012276:Ricin; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; D000074405:Valosin Containing Protein