Ubr1 and Ubr2 function in a quality control pathway for degradation of unfolded cytosolic proteins.
Quality control systems facilitate polypeptide folding and degradation to maintain protein homeostasis. Molecular chaperones promote folding, whereas the ubiquitin/proteasome system mediates degradation. We show here that Saccharomyces cerevisiae Ubr1 and Ubr2 ubiquitin ligases promote degradation of unfolded or misfolded cytosolic polypeptides. Ubr1 also catalyzes ubiquitinylation of denatured but not native luciferase in a purified system. This activity is based on the direct interaction of denatured luciferase with Ubr1, although Hsp70 stimulates polyubiquitinylation of the denatured substrate. We also report that loss of Ubr1 and Ubr2 function suppressed the growth arrest phenotype resulting from chaperone mutation. This correlates with increased protein kinase maturation and indicates partitioning of foldable conformers toward the proteasome. Our findings, based on the efficiency of this quality control system, suggest that the cell trades growth potential to avert the potential toxicity associated with accumulation of unfolded or misfolded proteins. Ubr1 and Ubr2 therefore represent E3 components of a novel quality control pathway for proteins synthesized on cytosolic ribosomes.
Nillegoda
Nadinath B
NB
Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY 10029, USA.
Theodoraki
Maria A
MA
Mandal
Atin K
AK
Mayo
Katie J
KJ
Ren
Hong Yu
HY
Sultana
Rasheda
R
Wu
Kenneth
K
Johnson
Jill
J
Cyr
Douglas M
DM
Caplan
Avrom J
AJ
D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D049409:Luciferases, Firefly / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination; D056811:Unfolded Protein Response / Q000502:physiology*
D018840:HSP70 Heat-Shock Proteins; D010455:Peptides; D061988:Proteasome Inhibitors; D029701:Saccharomyces cerevisiae Proteins; D049409:Luciferases, Firefly; C066066:UBR1 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases; C496536:Ubr2 protein, S cerevisiae; D017868:Cyclic AMP-Dependent Protein Kinases; C457179:TPK2 protein, S cerevisiae; D046988:Proteasome Endopeptidase Complex
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