The Coming Wave Page #25
Q: Not much. It is a virus and from our lessons this winter I know that it has some similar mechanisms as the Influenza A virus.
MA: Yes it is a virus, it is called HIV. It stands for the Human Immunodeficiency Virus and is a Retrovirus.
The target cells for HIV are immune cells, called CD4+T cells, these cells help the body fight infection and disease. But they are HIV's primary target.
HIV is spherical in shape. The outer coat of the virus, known as the viral envelope, is composed of two layers of fatty molecules called lipids, taken from the membrane of a human cell when a newly formed virus particle buds from the cell.
MA: Does that sound familiar?
Q: Very much so - that sounds just like the Influenza A virus.
MA: Yes indeed it does.
Also similar is that embedded in the viral envelope are proteins from the host cell, as well as copies of a complex HIV protein (frequently called “spikes”) that protrudes through the surface of the virus particle.
This protein, known as Env, consists of a cap made of three molecules called glycoprotein (gp) 120, and a stem consisting of three gp41 molecules that anchor the structure in the viral envelope.
When you think back to the functions of HA and NA in the Influenza A virus, GP 120 is very similar.
The HIV glycoproteins aid in its attachment to the target cells - CD4, the primary HIV-1 receptor.
This binding exposes a site on gp120 that enables interactions with secondary coreceptors and further conformational changes. Remember how the HA in H1N1 unfolds and attaches.
Q: Yes, that is a very dramatic little trick it does.
MA: But the point is that the viral structure in both these pathogens, while differing in many key ways, is fundamentally a variation of the same form.
Q: OK I understand that, but why is it important?
MA: I believe it to be very important. But before we get back to how patterns of glycosylation of a virus can be an important factor in its virulence, would you indulge me in a bit of a sidebar?
Q: Why of course.
MA: When we had our original discussion last summer and I explained to you that I had very serious concerns about our vulnerability, as a species, to emerging pathogens you thought that H1N1 was my major worry - did you not?
Q: Yes - I assumed it was the flu - what with your log in name and such.
MA: Well, the answer is both yes and no. As with much of science - when you hear hoof beats it is normally a horse - but occasionally it is a zebra.