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<p>Protein quality control (PQC) in the secretory pathway, a process critically linked to numerous human diseases, begins in the endoplasmic reticulum (ER) and involves ER-associated degradation (ERAD) of terminally misfolded proteins. In this study, we conducted genome-wide screens in baker’s yeast (<i>Saccharomyces cerevisiae</i>) to investigate the degradation of Gas1*, a misfolded version of an O-mannosylated, glycosylphosphatidylinositol (GPI)-anchored protein. In combination with detailed biochemical and genetic analyses, these screens revealed an unexpected bifunctionality of the evolutionarily conserved heteromeric enzyme complex Pbn1-Gpi14: while it has been previously recognized as a GPI-mannosyltransferase, we here find that it catalyzes the O-mannosylation of misfolded proteins, thereby promoting their ERAD. This process is particularly relevant for misfolded proteins that lack N-glycans. Our results suggest that protein O-mannosylation constitutes a distinct type of glycan-dependent mechanism for promoting ERAD.</p>

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O-mannosylation of misfolded ER proteins promotes ERAD

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月5日

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  • Leticia Lemus,
  • Hadar Meyer,
  • Ana I Rodríguez-Rosado,
  • Maya Schuldiner,
  • Veit Goder

摘要

Protein quality control (PQC) in the secretory pathway, a process critically linked to numerous human diseases, begins in the endoplasmic reticulum (ER) and involves ER-associated degradation (ERAD) of terminally misfolded proteins. In this study, we conducted genome-wide screens in baker’s yeast (Saccharomyces cerevisiae) to investigate the degradation of Gas1*, a misfolded version of an O-mannosylated, glycosylphosphatidylinositol (GPI)-anchored protein. In combination with detailed biochemical and genetic analyses, these screens revealed an unexpected bifunctionality of the evolutionarily conserved heteromeric enzyme complex Pbn1-Gpi14: while it has been previously recognized as a GPI-mannosyltransferase, we here find that it catalyzes the O-mannosylation of misfolded proteins, thereby promoting their ERAD. This process is particularly relevant for misfolded proteins that lack N-glycans. Our results suggest that protein O-mannosylation constitutes a distinct type of glycan-dependent mechanism for promoting ERAD.