Molecule of the Month: Messenger RNA Capping
Messenger RNA molecules are capped with an inverted nucleotide
Putting on the Cap
Capping in Action
Taking the Cap Off
Exploring the Structure
Chlorella virus capping enzyme (PDB entries 1ckm, 1ckn and 1cko)
The GMP-adding enzyme opens and closes during its complicated reaction. It performs the reaction in two steps. First it finds a molecule of GTP, closes around it, and attaches the nucleotide to one of its own lysine amino acids. Then, it opens up and releases the pyrophosphate that it removed from GTP, and closes around the end of the mRNA, performing the nucleotide-transfer reaction. After these two steps it opens back up to release the capped mRNA. Researchers have captured a viral form of the enzyme in several of these steps (PDB entries 1ckm , 1ckn and 1cko ). Click on the image to see an interactive Jmol that shows the structures.
Topics for Further Discussion
- PDB entries (3rtx and 1p16) show a small portion of the C-terminal tail of RNA polymerase bound to a capping enzyme.
- The ligand in PDB entry 1cko is an analogue of the capped mRNA. Take a close look at the structure and determine what part of the ligand is the added nucleotide, and what part represents the mRNA.
January 2012, David Goodselldoi:10.2210/rcsb_pdb/mom_2012_1