UUG, according to the genetic code, is Leucine.
The latter is a leucine metabolite produced in the body through oxidation of the ketoacid of leucine (ketoisocaproate, KIC).
It is associated with a mutation of a phenylalanine to leucine in SEC23A.
The binding of Phe and the triptan is caused by π stacking interactions of the indole and amino acid and an additional effect on this interaction is because of dispersive effect of amino acid leucine (Leu)(not shown in figure 2).