Bean homologs of the mammalian glucose-regulated proteins: induction by tunicamycin and interaction with newly synthesized seed storage proteins in the endoplasmic reticulum.
Treatment of developing bean cotyledons with the inhibitor of N-glycosylation tunicamycin enhanced the synthesis of at least two polypeptides with molecular mass 78 kDa and 97 kDa. Pulse-chase experiments and subcellular fractionation indicated that these are endoplasmic reticulum (ER) residents. The 78 kDa protein is a major component of the ER protein fraction and, by N-terminal sequencing, was identified as a bean homolog of the mammalian 78 kDa glucose-regulated protein (GRP78). This is a molecular chaperone that is probably involved in the folding and oligomerization of several animal and yeast proteins in the ER. When newly synthesized storage glycoproteins phaseolin, phytohemagglutinin or alpha-amylase inhibitor were immunoprecipitated from an ER preparation of tunicamycin-treated tissue, the GRP78 homolog was always co-precipitated. Bound GRP78 homolog could be released by ATP treatment. These results suggest that, at least when glycosylation is inhibited, this protein plays a role in the early stages of the synthesis of vacuolar storage proteins.
Istituto Biosintesi Vegetali, Consiglio Nazionale delle Ricerche, Milano, Italy.
L
L
D'Amico
B
B
Valsasina
M G
MG
Daminati
M S
MS
Fabbrini
G
G
Nitti
R
R
Bollini
A
A
Ceriotti
A
A
Vitale
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000302:isolation & purification / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D007887:Fabaceae / Q000187:drug effects / Q000378:metabolism*; D006360:Heat-Shock Proteins; D008322:Mammals; D051379:Mice; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D015388:Organelles / Q000378:metabolism; D010940:Plant Proteins / Q000096:biosynthesis* / Q000302:isolation & purification / Q000378:metabolism; D010946:Plants, Medicinal; D012639:Seeds / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014415:Tunicamycin / Q000494:pharmacology*
D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D018832:Molecular Chaperones; D010940:Plant Proteins; D014415:Tunicamycin