Structural and Mechanistic Insights into the Latrophilin3-FLRT3 Complex that Mediates Glutamatergic Synapse Development

Abstract

SUMMARY Latrophilins (LPHNs) are adhesion-like G protein coupled receptors implicated in attention-deficit/hyperactivity disorder (ADHD). Recently, LPHN3 was found to regulate excitatory synapse number through trans interactions with fibronectin leucine-rich repeat transmembrane 3 (FLRT3). By isothermal titration calorimetry, we determined that only the olfactomedin (OLF) domain of LPHN3 is necessary for FLRT3 association. By multi-crystal native-SAD phasing, we determined the crystal structure of the OLF domain. This structure is a five-bladed β-propeller with a Ca2+ ion bound in the central pore, which is capped by a mobile loop that allows the ion to exchange with the solvent. The crystal structure of the OLF/FLRT3 complex shows that LPHN3-OLF in the closed state binds with high affinity to the concave face of FLRT3-LRR with a combination of hydrophobic and charged residues. Our study provides structural and functional insights into the molecular mechanism underlying the LPHN3/FLRT3 contribution to the development of glutamatergic synapses.

Super-complexes of adhesion GPCRs and neural guidance receptors

“…Most protein–protein interactions shown for FLRT involve the LRR domain, which promotes cell adhesion via interaction with itself (homophilic) 2 or with Latrophilin 7 , and triggers cell repulsion by binding Unc5 receptors 1 4 5 . FLRT–FLRT and FLRT–Latrophilin interactions are mediated by overlapping binding sites on the concave face of the LRR 6 12 13 . Repulsive FLRT–Unc5 interactions are mediated via a distinct binding site at a lateral side of the FLRT LRR 5 .…”

“…The interaction of these ligands with Latrophilin is best understood in the context of trans -cellular adhesion 7 28 30 . Using mutagenesis, we recently mapped the FLRT-binding site on the Latrophilin Olf domain 6 , which was further defined by recent structural analysis of dimers formed by FLRT3 LRR and Latrophilin3 Olf (refs 12 , 13 ). Interestingly, a cell-based binding assay suggested that Latrophilin, FLRT and Unc5 form a ternary complex 13 , although the structural arrangement of the ternary interaction remained elusive.…”

A Nonsynonymous Change in Adhesion G Protein–Coupled Receptor L3 Associated With Risk for Equine Degenerative Myeloencephalopathy in the Caspian Horse

“…ADGRL3, also known as LPHN3, is a member of the latrophilin subfamily of secretin G protein coupled receptors that is expressed in the striatum, a part of the brain important for motor control and reward [27]. ADGRL3 is known to play a role in glutamatergic synapse development [28]. Loss of function in a homolog, lphn3.1, leads to a hyperactive motor phenotype in developing zebrafish and in the ADGRL1 knock-out mouse [29,30].…”

Calcium-ligand variants of the myocilin olfactomedin propeller selected from invertebrate phyla reveal cross-talk with N-terminal blade and surface helices

“…To date, the only other olfactomedin domain captured structurally in multiple configurations is latrophilin 3 (LPHN3), which harbors an Asn-Asp-Asp triad, which is coincidentally permuted in sequence compared with the myoc-OLF triad Asp-Asn-Asp. In the structure of mouse latrophilin 3 (MmLPHN3; PDB entry 4rml; Ranaivoson et al, 2015), the long top loop adopts an open conformation that is unique among all other OLF structures [ Supplementary Fig. S5(a)] and an Mg 2+ ion was found to be hexacoordinated to the equivalent of Asp478 [Asp436; Supplementary Fig.…”

“…High-resolution crystal structures of the $30 kDa fivebladed -propeller OLF domain are available for four subfamily members: olfactomedin-1 (Pronker et al, 2015;Hill et al, 2015), latrophilin (Lu et al, 2015;Ranaivoson et al, 2015;Jackson et al, 2016), myocilin (Donegan et al, 2015) and gliomedin (Han & Kursula, 2015;Hill et al, 2015). While the folds are nearly indistinguishable [ Fig.…”