Anticalins versus antibodies: made-to-order binding proteins for small molecules

Engineering proteins to bind small molecules presents a challenge as daunti ng as drug discovery, for both hinge upon our understanding of receptor-lig and molecular recognition. However, powerful techniques from combinatorial molecular biology can be used to rapidly select artificial receptors. While traditionally researchers have relied upon antibody technologies as a sour ce of new binding proteins, the lipocalin scaffold has recently emerged as an adaptable receptor for small molecule binding. 'Anticalins', engineered lipocalin variants, offer some advantages over traditional antibody technol ogy and illuminate features of molecular recognition between receptors and small molecule ligands.