Aromatic-aromatic and proline-aromatic interactions in endomorphin-1 and endomorphin-2

We investigated the aromatic-aromatic and proline-aromatic interactions in endomorphin-1 and endomorphin-2, and different types of these interactions were observed. For all the interacting pairs, the preferred geometric orientations were identified. We examined these interactions in the preferred secondary structures, which are different types of β-turns and γ-turns. These results revealed that the majority of the turn structures contained one of the interacting aromatic-aromatic or proline-aromatic pairs. On the basis of our results, it can be assumed that these interactions may be important in the determination and stabilization of the structures of endomorphins. Furthermore, our observations suggest that a conformation stabilized by an aromatic-aromatic or proline-aromatic interaction can play an important role in the association with the receptor.