Figure 2.

Structure of the pig OBP1. Tryptophan 16 is part of the lipocalin signature and is located outside the binding pocket. In a mutant designed to act as biosensing element for polyaromatic hydrocarbons, phenylalanine 88, which is located inside the binding pocket, was mutated into a second tryptophan residue, that would act as fluorescent reporter to monitor the presence of aromatic ligands in the binding site.