The lipocalin family is a large and diverse family of proteins with functions as small hydrophobic molecule transporters. Beta-lactoglobulin is a typical member of the lipocalin family. Beta-lactoglobulin was found to have a role in the transport of hydrophobic ligands such as retinol or fatty acids. Its crystal structure were determined Qin, 1998 with different ligands and in ligand-free form as well. The crystal structures determined so far reveal that the typical lipocalin contains eight-stranded antiparallel-barrel arranged to form a conical central cavity in which the hydrophobic ligand is bound. The structure of beta-lactoglobulin reveals that the barrel-form structure with the central cavity of the protein has an "entrance" surrounded by five beta-loops with centers around 26, 35, 63, 87, and 111, which undergo a conformational change during the ligand binding and close the cavity.