Molecule of the Month: TAL Effectors
TAL-effectors are modular, DNA-reading proteins that can be used to edit DNA in living cells
A TALE of Battle
Modular DNA Readers
Exploring the Structure
TAL Effector and DNA (PDB entry 3v6t)
By comparing TAL effectors from different bacteria, researchers have discovered modules for reading each of the bases in DNA, as well as a few modified forms of the bases. Each module is composed of a little bundle of two alpha helices. An amino acid at the inner edge of the module does the reading by contacting the edge of the nucleotide in the DNA, and a neighboring amino acid (not shown here) helps to position it. PDB entry 3v6t includes an engineered TAL effector with three types of modules. A module with aspartate, shown in red, forms a specific interaction with cytosine. However, a smaller glycine, shown in blue, makes a favorable interaction with the large methyl group of thymine. Serine, shown in green, forms a bond with adenine. Additional research is uncovering other modules to read the remaining base, guanine. To explore these modules and the entire structure in more detail, click on the image for an interactive JSmol.
Topics for Further Discussion
- You can see the structure of an engineered TAL effector before it binds to DNA in PDB entry 3v6p.
- Each TAL effector module is composed of two alpha helices with a small kink in one, which improves the packing between the two. Try displaying all prolines in these TAL effector structures to see the kink. Each module also includes a lysine and a glutamine that form non-specific interactions with the DNA backbone--see if you can find them.
December 2014, David Goodselldoi:10.2210/rcsb_pdb/mom_2014_12