Alrighty. I tried in the article; I hope you won't consider me lazy if I cut and paste a little.
At one time, it was believed that membrane proteins and fats were always scattered haphazardly throughout the lipid bilayer that makes up the cell membrane. The cell membrane surrounds all animal cells, and is generally made up of phospholipids (phosphates, PO4^3-, and lipids -- tiny fatty bits). These float around like little beachballs in a vast and sedate ocean:
What you’ve seen in every Biology textbook ever
The phospholipids are the brown bouncy bits.
Now, throughout the cell membrane are also proteins. Those are the blue guys. They let bigger molecules in and out of the cell. The carbohydrates that stick up (see the glycoprotein and glycolipid) help with cell recognition, which keeps you from attacking yourself. These are all in all your cells all the time: a vast sea of floaty things with cell bits -- mitochondria, nucleus, Golgi -- at the creamy center.
However, now there is a theory that there are fatty areas of the membrane, full of glycosphingolipids (sugar-amino alcohol-fatty bits), cholesterol, gangliosides, and proteins. These exist as little ‘pockets’ that go through the cell membrane, but they may be linear as well; and they tend to
cluster together when the cell is stressed. Stress here signifies anything that has the potential to cause cell damage, rather than to intimate that these cells are frightened or upset. (Last we checked, cells didn’t get very emotional.)
It's actually really fascinating the way it goes down. Actin -- which you may remember from studying muscle fibers -- actually yanks and drags proteins and fatty bits into place until there's like this little fatty warrior ready to do battle with any pathogen that tries to get past. There's a certain simple chemical barrier: it's hard to get past an oil slick. At the same time, lipid rafts are essential to signalling the cell to alert other cells to danger:
An interesting manner that allows pathogens to
evade the immune system is through membrane
microdomains. As signalling for the innate and
adaptative immune responses is initiated in rafts,
some pathogens have evolved mechanisms to subvert
this signalling by co-opting raft-associated pathways
(Ma˜ nes et al., 2003). Different pathogens, such as
viruses, bacteria and protozoa, can use the host-cell
lipid rafts to secure their entrance and maintenance
inside target cells.
From the excellent review article Host-cell lipid rafts: a safe door for micro-organisms? Did not find this one while writing the article but apparently
prions do this too guys.
So in order to defend the cell, lipid rafts aggregate, making it more challenging for a pathogen to enter both by simple polar (watery) vs nonpolar (fatty) inhibition at its most basic, as well as via some more complex immune mechanisms.
However, some bacterial and viral pathogens have evolved to not only get around this defense technique, but exploit it. By ‘sneaking in’ the cellular back-door, these pathogens also escape being sent to the lysosome for disposal, and may therefore survive longer than their traditionally-infectious counterparts.
When you look at a list of which pathogens use the lipid raft more like the secret entrance to the hidden underground lair of your cell... whaddaya know, all the usual ME pathogens are present and accounted for.
Now you can read about this in college-level textbooks, but as recently as the 2000-2010s, the existence of lipid rafts was hotly debated in cellular metabolic circles, and lingering traces of butthurt still linger.
This torrent of research notwithstanding, there remains heated discussion concerning matters as fundamental as what lipid domains look like—a discussion that peaked but reached little in the way of resolution at a recent conference (Euroconference on Microdomains, Lipid Rafts, and Caveolae; Tomar, Portugal, May 17–22, 2003).
WHAT HAPPENED, CELLULAR FOLK. THE INTERNET WANTS TO KNOW.
And
Despite all of the work published on lipid rafts, it is not clear whether everybody is studying the same thing or even studying what they intend to study.
Does it sound familiar?
Just goes to show that no branch of science is without its hotly debated madness. At least the article I'm citing was produced 10+ years ago: now lipid rafts are a much more respectable field of research than once they were.
-J
P.S. I attached a cool article on lipid rafts and pathogens.
