Scientists have long known that certain proteins get pieces of grease stuck on them-become ''prenylated,'' in chemical parlance. The addition of a hydrophobic group to a protein forms a lipid anchor that attaches the protein to the lipid membrane. Associations of different proteins in a section of compositionally distinct fatty membrane have been called ''lipid rafts.''
Just as a raft is a bunch of logs associated because a rope binds them together, allowing it to perform the function of floating, proteins associated with other proteins on a lipid raft may perform functions, Boxer said, though evidence for this is limited. These rafts may serve many functions such as reacting to stress, conferring immunity through antibody response, adhering to other cells and countering bacteria and toxins.
''Many proteins live in three dimensions for part of their life and in two dimensions for part of their life,'' Boxer said. ''They go back and forth. When you're in two dimensions, your chance of bumping into something else is a lot higher than when you're in three dimensions. This is the idea of the rafts. You get one of these pieces of grease stuck on you, and now you become associated with the membrane and you find yourself in one of these rafts, whatever they are, and now you meet your friends, and the result is specialized function. It's an organizing principle, if you like, in an otherwise fluid environment.''