Saturday, February 21, 2009

AH-CHOO!!!

(The genome of the common cold virus has been sequenced. I'm rather surprised it has taken so long. Anyway, as we have family visiting this week, I will use this important announcement as an excuse -- in my present good health -- to reprise a post of several years ago.)

Excuse me. I had meant to write about something else this morning -- the origin of the universe, perhaps, or the evolution of consciousness. But, you see, I have this...

AH-CHOO!!!

...this cold. My body has been hijacked. I don't feel like writing about anything. All I seem to be able to do is...

AH-CHOO!!!

...sneeze.

It's those viruses. Multiplying like crazy in my nose. They have irritant proteins on their surface that trigger my sneezes. It's part of their plan. They have ravaged my respiratory system in their reproductive frenzy, and now they're looking for another innocent victim, more cells to commandeer. So they irritate my nose. Ah-ah-AH......CHOO!!! An explosion. Ten thousand globules of moisture expelled at 40 miles per hour. Each globule packed with viruses. Ordinary common cold viruses. Now afloat in the air.

To drift into someone else's nose.

Whereupon they are propelled along in a film of mucus by a tiny oaring hairs, called cilia, to the back of the throat, where, if we are lucky, they are washed down to the gut and digested. End of story. But occasionally a virus binds to a cell in the nasal passages. And that's when the trouble begins.

The virus penetrates the cell. Inside, it unzips its protein coat exposing a bundle of naked genes. These pirate genes take over the cell's reproductive machinery and start making copies of themselves. Loads and loads of copies. A few days later the symptoms appear. The sore throat. The runny nose. The sneezing.

Cats don't get colds. Dog's don't get colds. Canaries and hippopotamuses don't get colds. Just humans and chimpanzees. We alone are the targets of these mischievous invaders. They are legion; at least 200 different kinds of viruses can cause a cold. The bewildering variety makes it hard for our bodies to muster defenses. And for scientists to provide a vaccine.

In spite of their differences, most cold-causing viruses are part of a family called rhinoviruses. Snips of genes in a protein coat. The coat is put together like a Buckminster Fuller dome. Sixty identical equilateral triangles, arranged in groups of five to make an almost-sphere, a perfect icosahedron. At the center of each group is a bump surrounded by a deep circular canyon, like a castle with a moat. Twelve castles and twelve moats on the surface of each virus. The castles differ from virus to virus. The moats are pretty much the same.

The bumps and canyons seem to be the key to the rhinoviruses' success. By the time our body has learned to recognize one virus by its bumps, and prepare antibodies that will attack and destroy the virus, along comes another virus with different bumps. The common cold virus is master of a hundred disguises.

But rhinoviruses must have something in common if they can all attach themselves to the same cells in our noses. What they seem to have in common is a binding mechanism hidden at the base of the deep and narrow moats, safely out of reach of antibodies.

Devilishly clever.

A few decades ago we knew very little about the viruses that cause the common cold. Today, we know their structure, almost atom by atom. A cure for the common cold may not be in sight, but drugs that prevent infection appear to be possible. Such drugs might prevent a virus from binding to cells in the nose, or from unzipping its coat once it is inside a cell.

Scientists can be devilishly clever too.

Clever enough to figure out the structure of something that is much too small to see. Ten thousand rhinoviruses can line up on the head of a pin, and a simple icosahedral shape with bumps and canyons is all they need to render my body completely miserable.

Who would have guessed that the cause of such mischief is a thing of such simple elegance.

The common cold virus has reduced life to its essence: genes making copies of themselves. They eschew the usual apparatus of reproduction. No flowers or bright plumage or paired sexes. No warbling or chirping or whispering sweet nothings. Just opportunistic genes in a protein jacket. The jacket protects the genes and binds the virus to a cell in the human nose. The invaded cell provides what the virus needs to reproduce.

A cold virus alone on a desert island could never make copies of itself. Two cold viruses alone on a desert island could never make copies of themselves. They need me...

AH-CHOO!!!

...and you.

They need a nose.