Fig. 5. Do IgLONs form heterodimers in cis? We propose that IgLONs preferentially form heterodimers on the surface of neurons. The homodimeric IgLON-Fc proteins might not bind to the heterodimers because dimerization induces a conformational change that interferes with binding, because of steric hindrance or because the affinity of one head to one of the heterodimeric subunits is too low to stabilize the complex.