Env (gene)
| env gp160; envelope glycoprotein | |
|---|---|
| Identifiers | |
| Organism | |
| Symbol | env |
| Entrez | 155971 |
| RefSeq (Prot) | NP_057856.1 |
| UniProt | P04578 |
| Other data | |
| Chromosome | viral genome: 0.01 - 0.01 Mb |
Env is a viral gene that encodes the protein forming 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 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.
The retroviral glycoproteins are oligomeric complexes that are composed of SU-TM heterodimers, which are made in the endoplasmic reticulum after the translation of the glycosylated Env precursor. The arrangement of these heterodimers determines the 3D structure of the knobbed spike on the viral surface. The Env proteins of the Avian Sarcoma and Leukosis virus (ASLV) and the Murine Leukemia Virus (MLV) are both trimers of SU-TM heterodimers. The Env protein of Human Immunodeficiency Virus (HIV) also has a trimeric structure of heterodimers. It is believed that the intracellular transport of the nascent protein depends, to some extent, on the oligomerization of Env precursors, which allows hydrophobic sequences to be buried inside the protein structure. This oligomerization has also been implicated in fusion initiation with the membrane of the target cell.
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