Molecule of the Month: Enhanceosome
Enhanceosomes help decide the appropriate time to transcribe a gene
Integrating the Signal
Exploring the Structure
This model of the entire interferon-b enhancer was created by Daniel Panne based on several crystallographic structures (PDB entries 1t2k , 2pi0 , 2o6g and 2o61 ); click here for coordinates of the model). It reveals several surprising aspects of the assembly. First, it shows that the DNA is nearly straight--some researchers had predicted that the DNA would be significantly bent. Second, the interaction between the proteins is very limited, even though the binding of the proteins is known to be cooperative, such that binding of one protein promotes the binding of others. This may be a consequence of several things. Several of the proteins bind on opposite sides of the same part of the DNA, so the proteins may promote binding by distorting the DNA slightly into a preferred conformation. Also, the crystal structures of ATF-2/c-Jun and the IRF proteins were solved using only the DNA-binding portions of the proteins, so the missing portions of the proteins may interact cooperatively with their neighbors. Finally, inside cells, CREB-binding protein or p300 (shown on the previous page) might generate a strong cooperative effect through its binding to the different proteins. Click on the image to view an interactive Jmol version.
Topics for Further Discussion
- Additional structures of several of these proteins are available in the PDB. Are they similar in structure to the proteins in the enhanceosome complex?
- Many different protein folding motifs are used to recognize DNA. Can you find other examples in the PDB?
February 2010, David Goodselldoi:10.2210/rcsb_pdb/mom_2010_2