Story1. Does Absence of An Oxygen Atom in Sugar Make Us Human?
At this moment, an experiment is going on in a secret lab somewhere in Unites States to initiate probable spark of intelligence in a chimpanzee; its after all, elimination of an oxygen (O) atom from a sugar molecule called sialic acid, ubiquitous to our body. This tiny change initiates cascade of physiological changes including connectivity in brain cells and hence, learning and memory.
The story goes back to 1998 when Prof. Ajit Varki at UCSD demonstrated that chimps, baboons, gorillas and orangutans have a specific sialic acid molecule called N-glycolyl neuraminic acid (Neu5Gc). We, Homo sapiens, do not have this molecule; instead, we have another version of sialic acid called N-acetyl neuraminic acid (Neu5Ac). The only difference between these two molecules is the presence of an oxygen atom in Neu5Gc and this changes the way proteins interact with each other, carbohydrates interact with each other and protein interact with carbohydrates. A small change in organic structure can have prodigious biological ramifications such as our vulnerability to HIV (apes do not get infected with HIV), Alzheimer's Disease, multiple sclerosis.
We have a faulty gene and therefore, a faulty protein that fails to convert Neu5Ac to Neu5Gc. If this protein starts to function, we will have early cancer, inflammation, platelet dysfunctions etc. Prof. Varki believes that evolutionary pressure to cope with malarial parasite Plasmodium reichenowi in African jungle brought about this change in our gene. In the meantime, malarial parasite also evolved into Plasmodium falciparum in order to hook on to Neu5Ac present on red blood cells of human. Thus, the deletion of oxygen atom helped us survive for sometime, but, it came with other trade-offs. For example, it is now established that HIV-1 enters human immune cells after communicating with Neu5Ac. However, this sugar molecule might have tremendous role in memory and learning in humans and it is possible that the faulty gene has made us intelligent ape!
(Reference. Nature, 2008, 454, 21-23)
Story2. Are We One Avian Flu Mutation Away from Extinction?
Extremely contagious influenza virus has hit us from ages but, avian influenza virus invasion is a rare event. Viral protein, hemagglutitin (HA) talks with the sugar-sugar conjugate, Neu5Ac-Galactose (linkage 2-6) present on our respiratory cells and get permission to enter. This virus, then, makes home at the upper respiratory tract and spread through human to human contact, but, this virus is innocuous unlike avian flu. Bird flu is not only highly contagious but also extremely lethal among birds. It can hardly cross the inter-species barrier as it cannot communicate with our Neu5Ac-Galactose (linkage 2-6) but, only with a structural analog, Neu5Ac-Galactose (linkage 2-3), found in minor population of epithelial cells deep within lungs.
How did avian flu cross the bird to man species barrier in 2006 causing 108 deaths worldwide? It was lower respiratory tract infection through Neu5Ac-Galactose (linkage 2-3) recognition in human. Luckily, this lethal virus home at the lower respiratory tract for infection and hence, prevents human to human transfer.
Let me bring the scary aspect of mutation and our chance of extinction to fatal contagious influenza virus. The virus particles always reproduce when in contact with a living object. What if one of these reproductions initiate a mutation in the viral protein, hemagglutitin (HA) triggering human sugar-sugar linkage (linkage 2-6) recognition? This will spell havoc among humanity as this new strain of avial flu will be able to invade the upper respiratory tract heavily populated with Neu5Ac-Galactose (linkage 2-6) and therefore, easily spread among humans. Extinction will be a an overstatement, but, about fifty million people died in 1918 due to influenza virus (H1N1), possibly an avian strain (or, swine). The bottom line is that we are just a mutation away from our sugar-sugar connection to be detected by a lethal virus. Can we save ourselves from this evolving devil?
(Reference. Science, 2006, 312, 404-410)
