Other hydrogen bond formation: Together with a primary H-bond, the ligands also form a H-bond between, for example, hydroxyl group (OH) at R2 to carbonyl group (C=O) of Val 238, or thiol group (SH) at R2 to thiol group (SH) of Val 238, or amide group (NH) at R2 to carbonyl group (C=O) of Val 238, or thiol group (SH) at R2 to thiol group (SH) of Cys 241.