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Free keywords:
RETICULUM-ASSOCIATED DEGRADATION; NUCLEAR-MEMBRANE PROTEINS;
ER-ASSOCIATED DEGRADATION; UBIQUITIN LIGASE; QUALITY-CONTROL; SQUALENE
MONOOXYGENASE; DOA10; REDUCTASE; TRANSLOCATION; MECHANISMSScience & Technology - Other Topics;
Abstract:
Transmembrane E3 ligases play crucial roles in homeostasis. Much protein and organelle quality control, and metabolic regulation, are determined by ER-resident MARCH6 E3 ligases, including Doa10 in yeast. Here, we present Doa10/MARCH6 structural analysis by cryo-EM and AlphaFold predictions, and a structure-based mutagenesis campaign. The majority of Doa10/MARCH6 adopts a unique circular structure within the membrane. This channel is established by a lipid-binding scaffold, and gated by a flexible helical bundle. The ubiquitylation active site is positioned over the channel by connections between the cytosolic E3 ligase RING domain and the membrane-spanning scaffold and gate. Here, by assaying 95 MARCH6 variants for effects on stability of the well-characterized substrate SQLE, which regulates cholesterol levels, we reveal crucial roles of the gated channel and RING domain consistent with AlphaFold-models of substrate-engaged and ubiquitylation complexes. SQLE degradation further depends on connections between the channel and RING domain, and lipid binding sites, revealing how interconnected Doa10/MARCH6 elements could orchestrate metabolic signals, substrate binding, and E3 ligase activity.
Transmembrane E3 ligases are crucial in cellular homeostasis and metabolic regulation. Here, the authors provide the structural details of the ER-resident E3 ligase MARCH6/Doa10, uncovering its unique circular membrane structure and its role in ubiquitylation processes, essential for protein quality control.
