Identifying a Structural Basis for Plexin A3 Homomeric Interactions

Plexins are large transmembrane receptors known to interact with neuropilin 2 co-receptors and semaphorin ligands to regulate neuronal development. These receptors and ligands have recently been implicated in assisting cancer metastasis. While it is understood that plexin signaling occurs via Ras GTPase-activating proteins (Ras GAPs) and semaphorin binding occurs extracellularly, little is understood about the role of the transmembrane (TM) and cytosolic juxtamembrane (CYTO) regions in signaling and oligomerization. In this study, we focus on plexin A3 (PlA3) and show that individual amino acids in the TM and CYTO regions influence homooligomerization and, subsequently, function. We propose a model for the PlA3 oligomerization interface and use site-directed mutagenesis and the AraTM method to identify the role of individual amino acids in the TM-CYTO region that influence this oligomerization. Bioluminescent resonance energy transfer was used to confirm the impact of select amino acids on oligomerization in a mammalian cell membrane with a truncated receptor.