Zinc Finger Domain Animation

Zinc fingers are small protein domains that can coordinate one or more zinc ions to help stabilize their folds. They can be classified into several different structural families and typically function as interaction modules that bind DNA, RNA, proteins or small molecules. The name "zinc finger" was coined to describe the hypothesized structure of the repeated unit in Xenopus laevis transcription factor IIIA.



Classes

Zinc fingers coordinate zinc ions with a combination of cysteine and histidine residues. They can be classified by the type and order of these zinc coordinating residues (e.g. Cys2His2, Cys4, and Cys6). A more systematic method classifies them into different "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.

Cys2His2

The Cys2His2-like fold group is by far the best characterized class of zinc fingers and are extremely common in mammalian transcription factors. These domains adopt a simple ββα fold and have the amino acid Sequence motif: X2-Cys-X2,4-Cys-X12-His-X3,4,5-His This class of zinc fingers can have a variety of functions such as binding RNA and mediating protein-protein interactions, but is best known for its role in sequence specific DNA-binding proteins such as Zif268. In such proteins, individual zinc finger domains typically occur as tandem repeats with two, three or more fingers comprising the DNA-binding domain of the protein. These tandem arrays can bind in the major groove of DNA and are typically spaced at 3-bp intervals. The α-helix of each domain (often called the "recognition helix") can make sequence specific contacts to DNA bases; residues from a single recognition helix can contact 4 or more bases to yield an overlapping pattern of contacts with adjacent zinc fingers.

Gag knuckle

This fold group is defined by two short β-strands connected by a turn (zinc knuckle) followed by a short helix or loop and resembles the classical Cys2His2 motif with a large portion of the helix and β-hairpin truncated. The best characters members of this family are found in the retroviral nucleocapsid (NC) protein from HIV and other related retroviruses. The gag knuckle zinc finger in the HIV NC protein is the target of a class of drugs known as zinc finger inhibitors.


Treble clef

The treble clef motif consists of a β-hairpin at the N-terminus and an α-helix at the C-terminus that each contribute two ligands for zinc binding, although a loop and a second β-hairpin of varying length and conformation can be present between the N-terminal β-hairpin and the C-terminal α-helix. These fingers are present in a diverse group of proteins that frequently do not share sequence or functional similarity with each other. The best characterized proteins containing treble clef zinc fingers are the [nuclear hormone receptors].

Zn2/Cys6

The canonical members of this class contain a binuclear zinc cluster in which two zinc ions are bound by six cysteine residues. These zinc fingers can be found in several transcription factors including the yeast Gal4 protein.


"Zinc finger." Wikipedia, The Free Encyclopedia. 16 Sep 2009, 10:25 UTC. 16 Sep 2009 <http://en.wikipedia.org/w/index.php?title=Zinc_finger&oldid=314315524>. 

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