Env

Env is a protein that is encoded by the env gene in the genome of retroviruses, including the Human Immunodeficiency Virus (HIV). The Env protein plays a crucial role in the virus's ability to infect host cells. It is composed of two subunits: gp120 and gp41, which are responsible for the virus's ability to bind to and fuse with host cells, respectively.

Structure

The Env protein is a trimer, meaning it is composed of three identical subunits. Each subunit is made up of two parts: the surface unit gp120 and the transmembrane unit gp41. The gp120 unit is responsible for binding to the CD4 receptor on the surface of host cells, while the gp41 unit facilitates the fusion of the viral and host cell membranes.

Function

The primary function of the Env protein is to facilitate the entry of the virus into host cells. This is achieved through a two-step process. First, the gp120 unit of the Env protein binds to the CD4 receptor on the surface of the host cell. This binding triggers a conformational change in the gp120 unit, allowing it to bind to a second receptor, known as a co-receptor. Once the gp120 unit has bound to the co-receptor, the gp41 unit undergoes a conformational change that allows it to insert into the host cell membrane and facilitate the fusion of the viral and host cell membranes.

Clinical significance

The Env protein is a major target for HIV vaccine development. Because it is the only viral protein exposed on the surface of the virus, it is the primary target for neutralizing antibodies. However, the high variability of the Env protein, particularly the gp120 unit, has made the development of an effective vaccine challenging.

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