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The helix-turn-helix motif is a DNA-binding motif. The recognition and binding to DNA by helix-turn-helix proteins 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 ...
HTH motif alignment of three TetR family members: MtrR (magenta), SimR (cyan), & AmtR (green) As of June 2005, this family of proteins had about 2,353 members that are transcriptional regulators. [1] (Transcriptional regulators control gene expression.) These proteins contain a helix-turn-helix (HTH) motif that is the DNA-binding domain.
Originally discovered in bacteria, the helix-turn-helix motif is commonly found in repressor proteins and is about 20 amino acids long. In eukaryotes, the homeodomain comprises 2 helices, one of which recognizes the DNA (aka recognition helix). They are common in proteins that regulate developmental processes.
An individual motif usually consists of only a few elements, e.g., the 'helix-turn-helix' motif which has just three. Note that, while the spatial sequence of elements may be identical in all instances of a motif, they may be encoded in any order within the underlying gene. In addition to secondary structural elements, protein structural motifs ...
When viewed from the N-terminal side of the beta strands, so that one strand is on top of the other, a left-handed beta-alpha-beta motif has the alpha helix on the left side of the beta strands. The more common right-handed motif would have an alpha helix on the right side of the plane containing the beta strands. [4]
Alpha solenoid proteins are composed of repeating structural units containing at least two alpha helices arranged in an antiparallel orientation. Often the repeating unit is a helix-turn-helix motif, but it can be more elaborate, as in variants with an additional helix in the turn segment. [2]
The N-terminus begins with one beta sheet composed of strands 1, 2, 3, and 4, followed by a helix-turn-helix motif of the two alpha helices, αA and αB, which continues into strands 5, 6, 7, and ending with one alpha-helical stalk at the C-terminus. αA and αB are perpendicular to one another, and because one end of αB is partially inserted ...
The secondary structure is assigned based on hydrogen bonding patterns as those initially proposed by Pauling et al. in 1951 (before any protein structure had ever been experimentally determined). There are eight types of secondary structure that DSSP defines: G = 3-turn helix (3 10 helix). Min length 3 residues. H = 4-turn helix . Minimum ...