Structural and functional insights into the latrophilin3 ‐ FLRT3‐UNC5D complex that mediates glutamatergic synapse development

Abstract

Latrophilins (LPHNs) are neuronal adhesion‐type G‐protein coupled receptors able to establish cell‐surface interactions with other proteins through their characteristically large ectodomain. Fibronectin leucine‐rich repeat transmembrane (FLRT) proteins constitute such endogenous ligands and the LPHN3‐FLRT3 trans‐cellular interaction has been shown to play an important role in glutamatergic synapse development in vitro and in vivo. With the use of a series of biochemical and biophysical techniques including analytical ultra‐centrifugation, deuterium‐exchange mass spectrometry, isothermal titration calorimetry and protein crystallography, we have performed an extensive characterization of the LPHN3‐FLRT3 interaction. In particular, 1) we have defined the binding domain of each partner to be the olfactomedin (OLF) domain in LPHN3 and the Leucin‐Rich Repeats (LRR) in FLRT3, 2) we have determined the crystal structure of the LPHN3‐OLF in two crystal forms, and 3) we have solved the crystal structure of the complex between LPHN3‐OLF and FLRT3‐LRR. In addition, 4) we have recently described higher‐ordered complexes formed by the LPHN‐FLRT sub‐complex and UNC5D, a receptor known to be implicated in axon guidance. Finally, 5) we are currently trying to identify novel ligands for some of these proteins. This work will enable us to understand, at the molecular level, the complex interplay of these proteins and their role in axon guidance and synapse formation.