title: Usa1 protein facilitates substrate ubiquitylation through two separate domains.
abstract: BACKGROUND
  Defects in protein folding are recognized as the root of many neurodegenerative disorders. In the endoplasmic reticulum (ER), secretory proteins are subjected to a stringent quality control process to eliminate misfolded proteins by the ER-associated degradation (ERAD) pathway. A novel ERAD component Usa1 was recently identified. However, the specific role of Usa1 in ERAD remains obscure.
  
  
  RESULTS
  Here, we demonstrate that Usa1 is important for substrate ubiquitylation. Furthermore, we defined key cis-elements of Usa1 essential for its degradation function. Interestingly, a putative proteasome-binding motif is dispensable for the functioning of Usa1 in ERAD. We identify two separate cytosolic domains critical for Usa1 activity in ERAD, one of which is involved in binding to the Ub-protein ligase Hrd1/Hrd3. Usa1 may have another novel role in substrate ubiquitylation that is separate from the Hrd1 association.
  
  
  CONCLUSIONS
  We conclude that Usa1 has two important roles in ERAD substrate ubiquitylation.
authors.affiliation: Institute of Biotechnology, University of Texas Health Science Center, San Antonio, Texas, USA. kimi@uthscsa.edu
authors.forename: Ikjin
authors.initials: I
authors.lastname: Kim
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.forename: Paulina
authors.initials: P
authors.lastname: Muniz
authors.forename: Hai
authors.initials: H
authors.lastname: Rao
mesh_terms: D000483:Alleles; D020816:Amino Acid Motifs; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D017353:Gene Deletion; D047468:Immunoprecipitation; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C546121:Usa1 protein, S cerevisiae; D046988:Proteasome Endopeptidase Complex