The co-receptor in this interaction is NPR1.
Takahashi et al. (1999)
found that the 2 semaphorin-binding proteins, plexin-1 (PLXN1) and neuropilin-1 (NRP1; 602069), form a stable complex. PLXN1 alone did not bind semaphorin-3A (SEMA3A; 603961), but the NRP1/PLXN1 complex had a higher affinity for SEMA3A than did NRP1 alone.
The immunoglobulin superfamily cell adhesion molecule (IgCAM) L1 has confer responsivness to Sema3A. The composition of the Sema3A receptor might be modular, with L1 and PlexA1 being recruited either together or independently for association to NP1 (Castellani et al. 2004)