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
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