Human immunodeficiency virus (HIV) is a lentivirus that causes acquired immunodeficiency syndrome (AIDS), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. Envelope glycoprotein GP120 (or gp120) is a glycoprotein exposed on the surface of the HIV envelope. The 120 in its name comes from its molecular weight of 120 kilodaltons. gp120 is essential for virus entry into cells as it plays a vital role in seeking out specific cell surface receptors for entry. Alternative Names: SU protein, HIV 1 gp120 protein, HIV 1 gp120 protein, gp120 protein, HIV-1 gp120 protein, HIV-1 gp120, Glycoprotein 120 protein, gp120 protein, HIV1 gp120, HIV-1 gp120 protein, HIV 1 gp120, Envelope surface glycoprotein gp120 protein, gp120 glycoprotein protein, Human Immunodeficiency Virus 1 protein, Surface protein protein