NCIt definition : A broad family of secreted proteins that bind to small hydrophobic molecules such
as steroids, bile pigments, retinoids and lipids and have an eight-stranded, antiparallel,
symmetrical beta-barrel, which forms the ligand binding site. These proteins play
a role in a number of biological processes, including immune responses, cell migration,
cellular differentiation, and transport of lipids and retinoids.;