Intro to ERVs: Envy my env

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.

Comments

#1 manigen
July 17, 2008

Viruses are amazing, aren’t they? To do so much with so little, achieving all these extraordinary things in a complex enviroment…

Dammit. Now I have protein envy.
#2 Rayven Alandria
July 17, 2008

I’m so glad you are making this blog. Thank you.
This is probably an ignorant question, but I’m going to ask it anyway. Can we develop a fake receptor that the HIV will think is more yummy,(a better fit), than our own?
#3 John Phillips, FCD
July 17, 2008

Love these posts almost as much as your grind the IDiots posts. Well more in fact because I always learn something while the grind the IDiot posts simply confirm what we already know, but they are fun
#4 mcmillan
July 17, 2008

Any protein Im studying is automatically the coolest protein on the planet.

NOOOOO, it’s my protein that’s the coolest. I made pretty much the same joke to my class when I had a chance to use my protein as an example a little while ago. Though that’s probably not too original for us egotistical scientists.
#5 Bill
July 17, 2008

Ok, been wanting to ask some questions for a bit and this seems to be a good post for it.
First, although I have always liked science, most of my current ‘learning’ comes from here, pz, livescience.com, etc.
Ok, 1st question…Do I understand it correctly that our genes have bits of viruses stuck in them, some we have in common with apes and therefore have had since our common ancestors? Depending on if I have the right, I will have serveral other questions.
thanks for your time..
#6 John Kwok
July 17, 2008

Hi Abbie,

One of your very best posts IMHO. So when are you going to summarize the Rockefeller University evolution symposium talks, especially for those of us organismic biology types (including yours truly and a certain Oakland, CA-based physical anthropologist who moderated one of the sessions there) who were present and thought the talks sounded as though they were written in Sanskrit or Klingon (or maybe both)?

Cheers,

John
#7 Atila
July 17, 2008

The thin I most like in Env is its dynamics, it has to match CD4, CCR5 or CXC4 and still scape from immune system
#8 Sili
July 17, 2008

Thank you.

Any comments on this malaria/aids dealie?
#9 Sven DiMilo
July 17, 2008

the coolest protein on the planet

Yeah, that would have to be hemoglobin. Or possibly ATP synthase. Motor proteins are pretty cool too.
YMMV!
#10 Jared
July 17, 2008

Sili, simply put, HIV-1 is easier to acquire without DARC, but it also progresses much slower.
#11 Mercurious
July 17, 2008

Bill @ #5: You are correct. Human DNA is filled with retrovisuses. There also happens to be a number of them that we share with many other mammals including our most recent ancestor with the apes. This link may help
#12 Mercurious
July 17, 2008

P.S. Bill if you would like more info on that just google “human erv”. Here is one journal article I found. Link
#13 Bill
July 17, 2008

Thanks for responding, Mercurious.
Ok, now that is confirmed, my next question.

If we are only passing on genes from the egg and sperm, at what point is the virus DNA getting in there to be passed on to our descendents?
Does the retrovirus invade all cells in the body? Or since the mother’s eggs are always there, is there a better chance this stuff gets passed on maternaly other than through the dad (who is sort of making sperm as he goes along through life)
Or am I totally off base on how the genes are passed?
I am always thinking about things and this has been bugging me.

Thanks again.
#14 Aught3
July 18, 2008

It’s not just the genes that get passed on in the eggs and sperm, each gamete carries an entire haploid complement of the individual’s genome (one of each chromosome). The genome includes the genes but also has other sequences e.g. centromeres, NORs,and ERVs. Any individual who inherited an ERV from mum or dad would have that ERV present in each of their cells and has the possibility of passing that ERV to their children.

The initial viral infection would have had to occur in a cell that was in the non-somatic line i.e. a cell that was the progenitor of gametes. An infection in a regular body cell would not be passed on to offspring.
#15 Mercurious
July 18, 2008

Lets take at an example. (Side note, this is all coming from my own personal very basic understanding. If anything I state is incorrect it’s my own fault.)

Example: Lets take the common cold virus. This virus attacks various body systems, so it could spread to a number of organs, but tend to work on specific areas (what areas I have no clue). With the virus’s in the blood stream they can go anywhere. In very very rare cases it may be possible for them to into sex cells before they are released, thus infecting the embryo.

Remember also ERV’s are not full viruses, but inactive fragments of viruses. So if a virus is only able to partially implant it’s own encoders, then it won’t create new viruses but simply become “dead weight”.

Hope this help some and hope I haven’t butchered the concepts to much.
#16 trrll
July 19, 2008

Remember also ERV’s are not full viruses, but inactive fragments of viruses. So if a virus is only able to partially implant it’s own encoders, then it won’t create new viruses but simply become “dead weight”.

Except that code is enriched in sequences that code for protein folds that function well as components of useful proteins. So evolutionarily speaking, it’s probably more like that “junk drawer” of random bits of tubing, connectors, and machine parts that is crucial to the function of every working laboratory.
#17 georges.genovese
July 25, 2008

Hi ERV,
Stupid question but would like it confirmed as stupid!

Retroviruses seem “designed” to pass genetic material from organisms of the same species.
Could this have originally (at the start of life) been an attempt at sexual reproduction which has gone horribly wrong and is now just a parasitic nuisance?
Thanks GG
#18 Samia
July 25, 2008

Awesome post!