GluD1 and GluD2 subunits (also known as delta 1 and 2) are the members of the delta family of ionotropic glutamate receptors. They are particularly puzzling, since they are unable to bind glutamate, but rather bind glycine and d ‐serine via their classical ligand binding domain (LBD). While GluD2 has been the subject of intensive research over the past decades, it is only recently that GluD1 received similar interest and very few studies compare the properties of these two membrane proteins. In their research article included in this issue, Masternak et al . resolved the 3D structure of the GluD1 LBD, compared its d ‐serine sensitivity with that of GluD2 and identified critical residues involved in the dynamics of the LBD.