HIV glycoprotein 120 (gp120) is a 480-amino acid envelope protein expressed on the surface of the HIV virion. This protein is a cleavage product of gp160 (encoded by env) and the protease furin. It is then glycosylated with long carrbohydrate chains, which are believed to help the virus avoid antibody recognition. Designed antibodies shown to be effective in binding gp120 were specfiic to the CD4-binding site (CD4bs). gp120 binds noncovalently with the transmembrane gp41 and can be shed from the viral surface.