Classes
Initially, the term zinc finger was used solely to describe DNA binding motif found in Xenopus laevis, however it is now used to refer to any number of structures related by their coordination of a zinc ion. In general, zinc fingers coordinate zinc ions with a combination of cysteine and histidine residues. Originally, the number and order of these residues was used to classify different types of zinc fingers ( e.g., Cys2His2, Cys4, and Cys6). More recently, a more systematic method has been used to classify zinc finger proteins instead. This method classifies zinc finger proteins into "fold groups" based on the overall shape of the protein backbone in the folded domain. The most common "fold groups" of zinc fingers are the Cys2His2-like (the "classic zinc finger"), treble clef, and zinc ribbon.
The following table shows the different structures and their key features:
| Fold Group | Representative structure | Ligand placement |
|---|---|---|
| Cys2His2 | Two ligands form a knuckle and two more form the c terminus of a helix. | |
| Gag knuckle | Two ligands form a knuckle and two more form a short helix or loop. | |
| Treble clef | Two ligands form a knuckle and two more form the N terminus of a helix. | |
| Zinc ribbon | Two ligands each form two knuckles. | |
| Zn2/Cys6 | Two ligands form the N terminus of a helix and two more form a loop. | |
| TAZ2 domain like | Two ligands form the termini of two helices. |
Read more about this topic: Zinc Finger
Famous quotes containing the word classes:
“Is a man too strong and fierce for society, and by temper and position a bad citizen,—a morose ruffian, with a dash of the pirate in him;Mnature sends him a troop of pretty sons and daughters, who are getting along in the dame’s classes at the village school, and love and fear for them smooths his grim scowl to courtesy. Thus she contrives to intenerate the granite and the feldspar, takes the boar out and puts the lamb in, and keeps her balance true.”
—Ralph Waldo Emerson (1803–1882)
“There are two classes of men called poets. The one cultivates life, the other art,... one satisfies hunger, the other gratifies the palate.”
—Henry David Thoreau (1817–1862)
“There were three classes of inhabitants who either frequent or inhabit the country which we had now entered: first, the loggers, who, for a part of the year, the winter and spring, are far the most numerous, but in the summer, except for a few explorers for timber, completely desert it; second, the few settlers I have named, the only permanent inhabitants, who live on the verge of it, and help raise supplies for the former; third, the hunters, mostly Indians, who range over it in their season.”
—Henry David Thoreau (1817–1862)