The Hungry Heart Of the Proteasome Comes into View Within the nuclear and cytoplasmic compartments of cells, the proteasome provides a way to regulate the function of key proteins. The proteasome, which is shaped like a dumbbell with trap doors at either end, plays a role in everything from cell cycle control to antigen presentation to neuronal pathfinding. It is also the most complex proteolytic assembly known. Inside the hollow center bar of the dumbbell, called the core particle, sits a protein-cutting mechanism. A ubiquitin tag attaches to proteins to be shuttled into this mechanism and destroyed.
Regulatory particles bind to the ends of the center bar, controlling the proteins' access.
The base binds to the core particle and contains a host of ATPases, which may convert chemical energy into molecular motion to shuttle some of the proteasome's targets into the core particle. However, the proteasome requires the aid of the lid complex to recognize ubiquitin-tagged proteins. Most surprisingly, say the researchers, the lid turns out to be intimately related to another protein complex that is used in the synthesis rather than the destruction of proteins, as well as a third particle that induces germination in plants. Proving itself an ever more ubiquitous form of communication, electronic mail may be working its way into patient-physician relationships. In a report published in the September 15 Annals of Internal Medicine, researchers outline potential benefits and pitfalls to widespread e-mail use in doctors' offices.