Faculty Opinions recommendation of Allosteric small molecules unveil a role of an extracellular E2/transmembrane helix 7 junction for G protein-coupled receptor activation.

The first intracellular loop (ICL1) of G protein-coupled receptors (GPCRs) has received little attention, although there is evidence that, with the 8th helix (H8), it is involved in early conformational changes following receptor activation as well as contacting the G protein β subunit. In class B1 GPCRs, the distal part of ICL1 contains a conserved R12.48KLRCxR2.46b motif that extends into the base of the second transmembrane helix; this is weakly conserved as a [R/H]12.48KL[R/H] motif in class A GPCRs. In the current study, the role of ICL1 and H8 in signaling through cAMP, iCa2+ and ERK1/2 has been examined in two class B1 GPCRs, using mutagenesis and molecular dynamics. Mutations throughout ICL1 can either enhance or disrupt cAMP production by CGRP at the CGRP receptor. Alanine mutagenesis identified subtle differences with regard elevation of iCa2+, with the distal end of the loop being particularly sensitive. ERK1/2 activation displayed little sensitivity to ICL1 mutation. A broadly similar pattern was observed with the glucagon receptor, although there were differences in significance of individual residues. Extending the study revealed that at the CRF1 receptor, an insertion in ICL1 switched signaling bias between iCa2+ and cAMP. Molecular dynamics suggested that changes in ICL1 altered the conformation of ICL2 and the H8/TM7 junction (ICL4). For H8, alanine mutagenesis showed the importance of E3908.49b for all three signal transduction pathways, for the CGRP receptor, but mutations of other residues largely just altered ERK1/2 activation. Thus, ICL1 may modulate GPCR bias via interactions with ICL2, ICL4 and the Gβ subunit.

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Dissociation of the intramolecularly cleaved N- and C-terminal fragments of the adhesion G protein-coupled receptor GPR133 (ADGRD1) increases canonical signaling

10.1101/2020.12.08.415398 ◽

2020 ◽

Author(s):

Joshua D. Frenster ◽

Gabriele Stephan ◽

Niklas Ravn-Boess ◽

Devin Bready ◽

Jordan Wilcox ◽

...

Keyword(s):

Plasma Membrane ◽

G Protein ◽

Receptor Activation ◽

List Type ◽

G Protein Coupled Receptor ◽

Major Mechanism ◽

N Terminus ◽

Adhesion Gpcr ◽

G Protein Coupled

SUMMARYGPR133 (ADGRD1), an adhesion G protein-coupled receptor (GPCR), is necessary for growth of glioblastoma (GBM), a brain malignancy. The extracellular N-terminus of GPR133 is thought to be autoproteolytically cleaved into an N-terminal and a C-terminal fragment (NTF and CTF). Nevertheless, the role of this cleavage in receptor activation remains unclear. Here, we show that the wild-type (WT) receptor is cleaved after protein synthesis and generates significantly more canonical signaling than an uncleavable point mutant (H543R) in patient-derived GBM cultures and HEK293T cells. However, the resulting NTF and CTF remain non-covalently bound until the receptor is trafficked to the plasma membrane, where we find NTF-CTF dissociation. Using a fusion of the hPAR1 receptor N-terminus and the CTF of GPR133, we demonstrate that thrombin-induced cleavage and shedding of the hPAR1 NTF increases receptor signaling. This study supports a model where dissociation of the NTF at the plasma membrane promotes GPR133 activation.Highlights-GPR133 is intramolecularly cleaved in patient-derived GBM cultures-Cleaved GPR133 signals at higher efficacy than the uncleavable GPR133 H543R mutant-The N- and C-terminal fragments (NTF and CTF) of GPR133 dissociate at the plasma membrane-Acute thrombin-induced cleavage of the human PAR1 NTF from the GPR133 CTF increases signalingeTOC BlurbFrenster et al. demonstrate intramolecular cleavage of the adhesion GPCR GPR133 in glioblastoma and HEK293T cells. The resulting N- and C-terminal fragments dissociate at the plasma membrane to increase canonical signaling. The findings suggest dissociation of GPR133’s N-terminus at the plasma membrane represents a major mechanism of receptor activation.

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