Molecule of the Month: Proteasome
Proteasomes destroy damaged or obsolete proteins inside cells
Engine of Destruction
Integrating Views of the Proteasome
Wearing a Different Cap
Exploring the Structure
Immunoproteasome (PDB entry 3unf)
Our cells also build specialized proteasomes for specific tasks. The one shown here, from PDB entry 3unf , is used during immune responses. When a cell is infected with viruses, it chops up the viral proteins and displays them on its surface with MHC, warning the immune system of the problem. A specialized proteasome, termed the immunoproteasome, is induced during the immune response and performs the cleavages. It is similar to the normal proteasome, but has three new catalytic subunits swapped into the core. One of these subunits cleaves the chain next hydrophobic amino acids, creating peptides that anchor particularly well to MHC. The illustration shows one ring of subunits, with an inhibitor (in turquoise) bound to the three catalytic subunits. To explore the immunoproteasome core in more detail, click on the image for an interactive Jmol.
Topics for Further Discussion
- Structures are available for several other large protein-cutting machines, including HslVU, ClpP, tricorn protease, and DegP.
- Several proteins are required to chaperone the assembly of proteasomes. You can explore the structures of these chaperones by searching for "proteasome assembly."
- Some archaea make much simpler proteasome cores that have the same shape as ours, but are composed of only two types of subunits. You can look at an example in PDB entry 1pma.
October 2013, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2013_10