Anticalin

Anticalins are artificial proteins that are able to bind to antigens, either to proteins or to small molecules. They are not structurally related to antibodies, which makes them a type of antibody mimetic. Instead, they are derived from human lipocalins which are a family of naturally binding proteins. Anticalins are being used in lieu of monoclonal antibodies, but are about eight times smaller with a size of about 180 amino acids and a mass of about 20 kDa.