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<p>The SEL1L-HRD1 complex represents the most conserved branch of endoplasmic reticulum (ER)-associated degradation (ERAD), a critical quality-control pathway that clears misfolded ER proteins. However, the molecular organization and pathogenic mechanisms of mammalian ERAD have remained elusive. Here, we report the cryo-EM structure of the core mammalian ERAD complex, comprising the ER lectin OS9, SEL1L, and the E3 ubiquitin ligase HRD1. The structure, validated by mutagenesis and crosslinking assays, reveals a dimeric assembly of the core complex in which SEL1L and OS9 form a claw-like configuration in the ER lumen that mediates substrate engagement, while HRD1 dimerizes within the membrane that may facilitate substrate translocation. Furthermore, pathogenic SEL1L mutations at the SEL1L-OS9 (Gly585Asp) and SEL1L-HRD1 (Ser658Pro) interfaces disrupt complex formation and impair ERAD activity. A newly identified disease-associated HRD1 variant (Ala91Asp), located in transmembrane helix 3, impairs HRD1 dimerization and substrate processing. These findings provide structural and functional insights for mammalian SEL1L-HRD1 ERAD and elucidate how mutations destabilizing this machinery contribute to human disease.</p>

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Structural basis and pathological implications of the dimeric OS9-SEL1L-HRD1 ERAD Core Complex

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月27日

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  • Liangguang Leo Lin,
  • Emir Maldosevic,
  • Linyao Elina Zhou,
  • Ahmad Jomaa,
  • Ling Qi

摘要

The SEL1L-HRD1 complex represents the most conserved branch of endoplasmic reticulum (ER)-associated degradation (ERAD), a critical quality-control pathway that clears misfolded ER proteins. However, the molecular organization and pathogenic mechanisms of mammalian ERAD have remained elusive. Here, we report the cryo-EM structure of the core mammalian ERAD complex, comprising the ER lectin OS9, SEL1L, and the E3 ubiquitin ligase HRD1. The structure, validated by mutagenesis and crosslinking assays, reveals a dimeric assembly of the core complex in which SEL1L and OS9 form a claw-like configuration in the ER lumen that mediates substrate engagement, while HRD1 dimerizes within the membrane that may facilitate substrate translocation. Furthermore, pathogenic SEL1L mutations at the SEL1L-OS9 (Gly585Asp) and SEL1L-HRD1 (Ser658Pro) interfaces disrupt complex formation and impair ERAD activity. A newly identified disease-associated HRD1 variant (Ala91Asp), located in transmembrane helix 3, impairs HRD1 dimerization and substrate processing. These findings provide structural and functional insights for mammalian SEL1L-HRD1 ERAD and elucidate how mutations destabilizing this machinery contribute to human disease.