The N Terminus of Adhesion G Protein–Coupled Receptor GPR126/ADGRG6 as Allosteric Force Integrator

Abstract

The adhesion G protein–coupled receptor (aGPCR) GPR126/ADGRG6 plays an important role in several physiological functions, such as myelination or peripheral nerve repair. This renders the receptor an attractive pharmacological target. GPR126 is a mechano-sensor that translates the binding of extracellular matrix (ECM) molecules to its N terminus into a metabotropic intracellular signal. To date, the structural requirements and the character of the forces needed for this ECM-mediated receptor activation are largely unknown. In this study, we provide this information by combining classic second-messenger detection with single-cell atomic force microscopy. We established a monoclonal antibody targeting the N terminus to stimulate GPR126 and compared it to the activation through its known ECM ligands, collagen IV and laminin 211. As each ligand uses a distinct mode of action, the N terminus can be regarded as an allosteric module that can fine-tune receptor activation in a context-specific manner.

Step-wise mechanical unfolding and dissociation of the GAIN domains of ADGRG1/GPR56, ADGRL1/Latrophilin-1 and ADGRB3/BAI3: insights into the mechanical activation hypothesis of adhesion G protein-coupled receptors

“…Only when the force duration timescale is comparable to or longer than those involved in GAIN domain unfolding and NTF/CTF dissociation can the findings from this study form a basis for interpreting aGPCR-mediated mechanosensing and mechanotransduction. Finally, our observations do not address how the observed GAIN unfolding and NTF/CTF dissociation lead to mechanical activation of aGPCRs, but previous studies have offered complementary approaches to investigate this in the future [62, 63]. Therefore, more comprehensive studies are needed to fully understand the role of mechanical activation in aGPCR signaling, which is the focus of our ongoing research.…”

Functional partnerships between GPI‐anchored proteins and adhesion GPCRs

“…[85][86][87] Moreover, an intact Stachel sequence and GPS cleavage is required for force-dependent GPR126-mediated signaling, suggesting the necessity of NTF-CTF dissociation for GPR126 activation. [11,88] Indeed, Petersen et al showed that binding of Schwann cell-derived laminin-211 matrix protein to GPR126 resulted in reduced and enhanced cAMP levels in a GPS proteolysis-dependent manner in static and vibration conditions, respectively. [77] Consistently, polymerization of laminin proteins in vivo was shown to be necessary for GPR126 activation, likely to provide a pulling force for NTF dissociation and the Stachel peptide-mediated signaling.…”

“…[ 85–87 ] Moreover, an intact Stachel sequence and GPS cleavage is required for force‐dependent GPR126‐mediated signaling, suggesting the necessity of NTF‐CTF dissociation for GPR126 activation. [ 11,88 ] Indeed, Petersen et al. showed that binding of Schwann cell‐derived laminin‐211 matrix protein to GPR126 resulted in reduced and enhanced cAMP levels in a GPS proteolysis‐dependent manner in static and vibration conditions, respectively.…”

The GPCR properties of polycystin-1- A new paradigm

“…It was postulated that 'flexing' of the GAIN domain might be modulated by the engagement of specific ligands to the GAIN domain itself (e.g., synaptamide), or to an adhesion domain within the ECR. Some groups have used the binding of synthetic ligands, such as antibodies directed at ECR domains or at ectopic N-terminal epitope tags, as a means to activate adhesion GPCRs (Salzman et al, 2017;Bhudia et al, 2020;Huang et al, 2020;Mitgau et al, 2022). Recently, the cryo-electron micrograph (EM) structures of the CTF subunit for a number of adhesion GPCRs were published by four groups (Barros-Alvarez et al, 2022;Ping et al, 2022;Qu et al, 2022;Xiao et al, 2022).…”