The cryo-EM structure of an ERAD protein channel formed by tetrameric human Derlin-1

Abstract

Endoplasmic reticulum–associated degradation (ERAD) is a process directing misfolded proteins from the ER lumen and membrane to the degradation machinery in the cytosol. A key step in ERAD is the translocation of ER proteins to the cytosol. Derlins are essential for protein translocation in ERAD, but the mechanism remains unclear. Here, we solved the structure of human Derlin-1 by cryo–electron microscopy. The structure shows that Derlin-1 forms a homotetramer that encircles a large tunnel traversing the ER membrane. The tunnel has a diameter of about 12 to 15 angstroms, large enough to allow an α helix to pass through. The structure also shows a lateral gate within the membrane, providing access of transmembrane proteins to the tunnel, and thus, human Derlin-1 forms a protein channel for translocation of misfolded proteins. Our structure is different from the monomeric yeast Derlin structure previously reported, which forms a semichannel with another protein.

Derlin rhomboid pseudoproteases employ substrate engagement and lipid distortion to enable the retrotranslocation of ERAD membrane substrates

“…Recent cryoelectron microscopy (cryo-EM) work demonstrated that Derlin-1 forms a tetrameric channel, and this complex was predicted to allow a single-transmembrane helix to pass through its pore during retrotranslocation (Rao et al, 2021). We wanted to determine whether Derlin-1 was able to induce lipid thinning as a tetrameric complex.…”

Maintenance of organellar protein homeostasis by ER-associated degradation and related mechanisms

“…Moreover, biochemical analysis of Doa10 and the Asi complexes revealed that these entities are sufficient for the retrotranslocation of ERAD-C substrates and orphan complex subunits, respectively (Natarajan et al, 2020;Schmidt et al, 2020). In addition, the structure of human Derlin1 was recently published (Rao et al, 2021), which postulates an entirely different route to the retrotranslocation of luminal and TM substrates. Human Derlin-1 and -2 contain a p97 interaction motif at their C terminus, which can serve to recruit p97 directly and fuel retrotranslocation.…”

How Viruses Use the VCP/p97 ATPase Molecular Machine

“…After recognition by BiP or other ER luminal proteins, Derlin-1 often is engaged for dislocation of proteins from the ER membrane. Derlin-1 is a multi-pass ER transmembrane protein that recently has been shown to be a homotetramer with a channel large enough to transfer a protein α-helix to the cytosol, i.e., to serve as a retrotranslocon [ 139 ]. Cytosolic E1 and E2 enzymes cooperate with ER transmembrane E3 ligases to ubiquitylate target proteins prior to recognition by adapters and VCP for delivery to the proteasome [ 124 ].…”