 However, asparagine 175 (Asn) in the TM4 domain is likely to be important for the MT2 receptor.The aromatic ring system in melatonin and analogues most likely contributes some binding affinity by binding to aromatic rings of the amino acids phenylalanine (Phe) and tryptophan (Trp) in the receptor.The bonds that form are van der Waals interactions.