Petrescu, S. M. | Search bioRxiv

bioRxiv2025

GPR27 mediates adrenergic ligands-induced transinhibition of EGFR

1.G-protein coupled receptor 27 (GPR27) is part of the "Super Conserved Receptors Expressed in Brain" (SREB) family, alongside GPR85 and GPR173. While the endogenous ligands and functions of SREB receptors are still unknown, GPR27 has been implicated in insulin secretion and tumorigenesis. Here, we show that substituting GPR27s C-terminus domain with that of the {beta}1 adrenergic receptor ({beta}1AR) yields a chimera with {beta}1AR-like ligand selectivity and cellular functions. Interestingly, adrenergic ligands stimulation of GPR27 inhibited EGF-induced serum-responsive element (SRE) activation, independently of G-proteins and {beta}-arrestins, through dephosphorylation of c-Src and EGFR proteins. This unique response was exclusive to GPR27, as GPR85 and GPR173 showed no similar effects. These findings suggest that GPR27 is a receptor responding to adrenergic ligands to transinhibit EGFR through an atypical signaling mechanism.

cell biology↗

bioRxiv2025

Structure and function of the EDEM:PDI ERAD checkpoint complex

The ERAD-L checkpoint complex de-mannosylates misfolded glycoproteins with lumenal defects, targeting them to retrotranslocation, ubiquitination, and proteasomal degradation. Commitment to ERAD-L requires an Endoplasmic Reticulum-Degradation Enhancing alpha-Mannosidase-like protein (EDEM) and its associated Protein Disulfide Isomerase (PDI). We determined Cryo-EM structures of the Chaetomium thermophilum EDEM:PDI heterodimer, both by itself and in complex with a classic ERAD substrate, the alpha1-antitrypsin Null Hong Kong mutant (A1AT-NHK). The EDEM catalytic domain nestles within the PDI arc. One intermolecular disulfide, between the a' domain of PDI and the first conserved cysteine of the EDEM linker (Cys A), stably links the two proteins. A second intermolecular disulfide, between the second conserved cysteine of the EDEM linker (Cys B) and the PDI a domain, stabilises the compact apo conformation. In the substrate-bound complex, the Cys B intermolecular disulfide is reduced and the catalytic CXXC motif of the PDI a domain oxidised. Release of the Cys B linkage increases the conformational freedom of the EDEM linker, allowing the EDEM C-terminal domains to adopt both proximal and distal conformations relative to the catalytic domain. The structures provide a framework for discovery of EDEM:PDI modulators, with potential applications in virology, rare genetic disease and cancer, and as reagents for glycoprotein quality-control engineering.

biochemistry↗