Env (gene)

Env (gene)

Env is a viral protein that serves to form the viral envelope. The expression of the env gene enables retroviruses to target and attach to specific cell types, and to infiltrate the target cell membrane. Analysis of the structure and sequence of several different env genes suggests that Env proteins are type 1 fusion machines. Type 1 fusion machines initially bind a receptor on the target cell surface, which triggers a conformational change, allowing for binding of the fusion protein. The fusion peptide inserts itself in the host cell membrane and brings the host cell membrane very close to the viral membrane to facilitate membrane fusion. While there are significant differences in sequence of the env gene between retroviruses, the gene is always located downstream of gag, pro, and pol. The env mRNA must be spliced for their expression. The mature product of the env gene is the viral spike protein, which has two main parts: the surface protein (SU) and the transmembrane protein (TM). The tropism of the virus is determined by the SU protein domain because it is responsible for the receptor-binding function of the virus. The SU domain therefore determines the specificity of the virus for a single receptor molecule.