The structural similarity and the amino acid sequence homology between RBP and the biliverdin-binding protein strongly indicate an evolutionary relationship between them. The common function of these two proteins is to bind large hydrophobic molecules, for which the up-and -down beta-barrel structure motif is particularly suited.The relationship between RBP and BBP helps the assignment of the function of the third member in RBP superfamily, beta-lactoglobulin.

The observation that beta-lactoglobulin is evolutionarily related to RBP prompted an investigation of the functional consequences of its ability to bind retinol. In vitro beta-lactoglobulin binds retinol more tightly than RBP. The studies suggest that specific receptors for the beta- lactoglobulin- retinol complex exist in the intestine of young calves and it involves in the vitamin A metabolism in suckling animals.