Last Saturday evening I went to a friends house to let Arnie play in their backyard, and today Im scratching a dozen mosquito bites.
But what does a virologist think when they get mosquito bites?
West Nile! WHOOOO!!!
And what does a girl who studies HIV-1 env think of when she thinks of West Nile?
Convergent evolution! WHOOOWHOOO!!!
WN was all over the news a few years ago because it can kill people. But there is no reason to be a spaz about it. Im under the impression that lots of us have been infected with WN, got a minor fever, and recovered without even noticing anything was wrong. No big whoop.
That being said, if you think youve been infected with West Nile, and your pretty sure your brain is inflamed, please stop clicking around on ScienceBlogs and consult a local physician.
However, if youre feeling fine and just want to learn about West Nile as a virus, I can help you there!
WN is a flavivirus like a couple of other fun viruses, Yellow Fever and Hepatitis C. Theyre ‘cake’ viruses (one big transcript gets cut into lots of little proteins) as opposed to ‘cupcake’ viruses (individual transcripts for each protein). Their structure is a lot like the common cold, except coated in a lipid bilayer stolen from the host cell. That means they need ‘envelope’ proteins (E proteins) sticking out to interact with new host receptors, as you can see in this diagram of Hepatitis Cs replication cycle.
Flaviviral E proteins are made of folded up beta-sheets. After they bind to their host cell receptor, the virus is taken up in an endosome through receptor mediated endocytosis. As the pH of the endosome gets lower, the beta-sheets change conformation and mediate the fusion of the virus lipid bilayer with the host membrane– the point where the virus actually infects the host cell.
This is where things get cool– Influenzas hemagglutanin protein does the exact same thing– Binds to the host cell receptor, changes conformation as the pH of the endosome lowers, mediates fusion of the two membranes to cause the actual ‘infection’ event… but influenza and West Nile arent related at all. Flaviviruses are single stranded (+) sense RNA. Influenzas genome is made of several chunks of single stranded (-) sense RNA! So how do these two viruses have almost identical replication strategies?
Flaviviral E proteins are beta sheets, influenzas hemagglutanin is made of alpha helices, but they ‘do’ the same thing! Just like insect and bat wings look totally different, but ‘do’ the same thing!