A Comprehensive Mutagenesis Screen of the Adhesion GPCR Latrophilin-1/ADGRL1

Abstract

SummaryAdhesion G-protein-coupled receptors (aGPCRs) play critical roles in diverse cellular processes in neurobiology, development, immunity, and numerous diseases. The lack of molecular understanding of their activation mechanisms, especially with regard to the transmembrane domains, hampers further studies to facilitate aGPCR-targeted drug development. Latrophilin-1/ADGRL1 is a model aGPCR that regulates synapse formation and embryogenesis, and its mutations are associated with cancer and attention-deficit/hyperactivity disorder. Here, we established functional assays to monitor latrophilin-1 function and showed the activation of latrophilin-1 by its endogenous agonist peptide. Via a comprehensive mutagenesis screen, we identified transmembrane domain residues essential for latrophilin-1 basal activity and for agonist peptide response. Strikingly, a cancer-associated mutation exhibited increased basal activity and failed to rescue the embryonic developmental phenotype in transgenic worms. These results provide a mechanistic foundation for future aGPCR-targeted drug design.

Beyond the Ligand: Extracellular and Transcellular G Protein–Coupled Receptor Complexes in Physiology and Pharmacology

“…The extracellular domains of ADGRLs have been demonstrated to associate with a remarkable diversity of synaptic adhesion molecules both in cis and in trans, as accounted below. Although ADGRLs are generally known for their contributions to extracellular structure, recent studies have conclusively demonstrated their ability to couple to canonical G protein pathways and thus serve as bona fide GPCRs (Li et al, 2018;Nazarko et al, 2018). Mechanistically, the multitude of extracellular and transcellular interactions of ADGRLs are capable of stabilizing various states of receptor activation/inactivation to coordinate cellular processes from neurite outgrowth, axonal attraction, and synaptogenesis to axonal repulsion and apoptosis.…”

C‐terminal phosphorylation of latrophilin‐1/ADGRL1 affects the interaction between its fragments

“…Indeed, when LTX N4C acts via the NTF–CTF complex, it clearly stimulates Gαq‐mediated signaling via PLC to internal Ca 2+ stores . On the other hand, the CTF of LPHN1 expressed without the NTF demonstrates a different signaling specificity and (at least when it is stimulated by exogenous Stachel peptide) activates Gαi, leading to a decrease in cAMP levels . Thus, the activation of one signaling pathway may cause the CTF to dissociate from the complex and switch to another signaling pathway, where the CTF could act as a nonadhesion GPCR.…”

The expanding functional roles and signaling mechanisms of adhesion G protein–coupled receptors

“…However, recent studies on the signaling mechanisms of aGPCRs have largely been aided by the development of signaling assays which can probe the functions of specific receptors. Previous works on ADGRL1 (latrophilin‐1) using newly established signaling assays have allowed a better understanding of how aGPCRs function and to probe the signaling effects of cancer mutations . Leon and colleagues found that ADGRL1 is activated by its Stachel peptide, similar to other aGPCRs, and studied the residues important for Stachel ‐mediated activation.…”

“…aGPCRs have large extracellular regions (ECRs) decorated by numerous adhesion domains and a conserved GPCR autoproteolysis inducing (GAIN) domain that mediates self‐cleavage of the receptor. Two avenues of research from her group were discussed: Araç and colleagues showed that aGPCRs are activated via Stachel ‐independent mechanisms in addition to Stachel ‐dependent mechanisms . Stachel ‐independent mechanisms depend on the large ECRs of aGPCRs and form the basis for the complex regulation of aGPCR function. They also determined the high‐resolution structure of teneurin, a large ligand of ADGRL1 (latrophilin/LPHN1) and revealed a unique structure that is similar to bacterial Tc toxins .…”

“…Araç and colleagues showed that aGPCRs are activated via Stachel ‐independent mechanisms in addition to Stachel ‐dependent mechanisms . Stachel ‐independent mechanisms depend on the large ECRs of aGPCRs and form the basis for the complex regulation of aGPCR function.…”