This next installment of ‘Intro to ERVs’ is about the coolest protein on the planet*, Env.
Weve got all the enzymes protected in their nice little core— but retroviruses are enveloped viruses. Theyre coated in the membranes of the cells they budded off of. Thats where env comes in! env codes for the protein that sticks out of the lipid membrane. It is responsible for binding to new host cells and mediating fusion between the viral membrane, and the target cell membrane.
To use HIV-1 as an example, the envelope gene codes for a ‘precursor protein’, glycoprotein160 (gp160). Its called a ‘glycoprotein’ because its coated in sugar. All the ‘Y’s on this diagram are where sugars can be covalently attached to the protein:
To keep using HIV-1 as an example, this precursor protein gets chopped in two, into a transmembrane gp41, which stays anchored in the viral membrane, and a subunit gp120, which is noncovalently attached to gp41 like a lolly-pop.
gp120 interacts with receptors on new host cells, gp41 mediates fusion (pic from ‘The challenges of eliciting neutralizing antibodies to HIV-1 and to influenza virus‘):
So there you have it! The three basic proteins that are found in every retrovirus:
- Gag– All the structural proteins
- Pol– All the necessary enzymes
- Env– Lets an enveloped virus attach and fuse with a new host cell
* Any protein Im studying is automatically the coolest protein on the planet. 😛