Envelope Glycoprotein GP120

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.

The crystal structure of gp120 complexed to D1D2 CD4 and a neutralizing antibody Fab was solved by Peter Kwong in 1998. It is organized with an outer domain, an inner domain with respect to its termini and a bridging sheet. The gp120 gene, env, is around 1.5 kb long and codes for around 500 amino acids. Three gp120s, bound as heterodimers to a transmembrane glycoprotein, gp41, are thought to combine in a trimer to form the envelope spike, which is involved in virus-cell attachment.

The Human Immunodeficiency Virus (HIV) can mutate frequently to stay ahead of the immune system. There is however a highly conserved region in the virus genome near its receptor binding site. The glycoprotein gp120 is anchored to the viral membrane, or envelope, via non-covalent bonds with the transmembrane glycoprotein, gp41. It is involved in entry into cells by binding to CD4 receptors, particularly helper T-cells. Binding to CD4 is mainly electrostatic although there are van der Waals interactions and hydrogen bonds.