We previously reported that LPHN3 binds in vivo and in vitro to fibronectin leucine-rich repeat transmembrane 3 (FLRT3) to constitute a synaptic ligand-receptor pair (O’Sullivan et al., 2012). Single particle electron microscopy of LPHN3 showed that its entire extracellular domain is organized into two globular regions separated by a semi-rigid domain that is O-linked glycosylated (O’Sullivan et al., 2014). However, these studies did not allow a detailed structural and functional characterization of the minimal domain necessary for the interaction with FLRT3. Here we show that only the OLF domain of LPHN3 is required for FLRT3-LRR binding and we determined precise dissociation constants and stoichiometry of the complex. As expected, the KD measured for this interaction (Table 1) are similar to the one determined for their entire extracellular domains (O’Sullivan et al., 2012), indicating that LPHN3-OLF alone is sufficient to bind FLRT3-LRR.
