Zinc finger motif

A single protein (one polypeptide chain) binds DNA through several consecutive zinc finger motifs.

This is a fragment (amino acid residues 1 to 101) of the TFIIIA transcription factor, from the frog Xenopus laevis, bound to 15 bp of the 5S RNA gene.

Quiz:

How many zinc finger motifs are shown?

The structure common with other proteins, and hence called the motif, consists in this case of a peptide segment in alpha helix and two in antiparallel beta sheet, in which there are 4 amino acids (2 Cys and 2 His) whose sidechains coordinate the Zn2+ ion; this kind of zinc finger is so called C2H2.    The atoms coordinating Zn (N in His and S in Cys) are highlighted.

Again, several consecutive C2H2 zinc finger motifs in the same polypeptide chain.

From the same protein, TFIIIA.

Quiz:

How many zinc finger motifs are shown?
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Another kind of zinc finger motif.

Human oestrogen receptor, bound to DNA.

In this case, the protein has a single zinc finger but forms a dimer when bound to DNA.

In addition, the motif has a different structure: two Zn2+ ions, each one coordinated by a helix and a loop, through the sidechains of 4 cysteines for each Zn ion.
This kind of motif is called a C4 zinc finger.