1. Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. Secreted extracellular proteins are often glycosylated.
  2. Glycoprotein is any of a class of conjugated proteins consisting of a compound of protein with a carbohydrate group.
    1. α1-acid glycoprotein an acute phase protein found in blood plasma, an indicator of tissue necrosis and inflammation. Called also orosomucoid.
    2. P-glycoprotein a cell-surface protein occurring normally in the colon, small intestine, adrenal glands, kidney, and liver, and also expressed by tumor cells. It is a modulator of multidrug resistance, mediating the transport of antineoplastic agents out of tumor cells.
    3. variable surface glycoprotein any of several glycoproteins that form the antigenic protein coating of Trypanosoma brucei. The organisms contain numerous genes encoding hundreds of such glycoproteins and, by expressing individual ones successively, evade the immune system of the host.