Helix-turn-helix

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The λ repressor of bacteriophage lambda employs a helix-turn-helix (top; green) to bind DNA (bottom; blue and red).

In proteins, the helix-turn-helix (HTH) is a major structural motif capable of binding DNA. It is composed of two α helices joined by a short strand of amino acids and is found in many proteins that regulate gene expression. Not to be confused with the Basic helix-loop-helix domain

Its discovery was based on similarities between the genes for Cro, CAP, and λ lambda repressor, which share a common 20-25 amino acid sequence that facilitates DNA recognition. In particular, recognition and binding to DNA is done by the two α helices, one occupying the N-terminal end of the motif, the other at the C-terminus. In most cases, such as in the Cro repressor, the second helix contributes most to DNA recognition, and hence it is often called the "recognition helix". It binds to the major groove of DNA through a series of hydrogen bonds and various Van der Waals interactions with exposed bases. The other α helix stabilizes the interaction between protein and DNA, but does not play a particularly strong role in its recognition.

See also

References

  • Brennan R, Matthews B (1989). "The helix-turn-helix DNA binding motif". J. Biol. Chem. 264 (4): 1903–6. PMID 2644244.

External links


Protein secondary structure
Helices: α-helix | 310 helix | π-helix | β-helix | Polyproline helix | Collagen helix
Extended: β-strand | Turn | Beta hairpin | Beta bulge | α-strand
Supersecondary: Coiled coil | Helix-turn-helix | EF hand
Secondary structure propensities of amino acids
Helix-favoring: Methionine | Alanine | Leucine | Glutamic acid | Glutamine | Lysine
Extended-favoring: Threonine | Isoleucine | Valine | Phenylalanine | Tyrosine | Tryptophan
Disorder-favoring: Glycine | Serine | Proline | Asparagine | Aspartic acid
No preference: Cysteine | Histidine | Arginine
←Primary structure Tertiary structure→

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