Heptad repeat
Encyclopedia
The heptad repeat is an example of a structural motif
that consists of a repeating pattern of seven amino acid
s:
a b c d e f g
H P P H C P C
where H represents hydrophobic residues, C represents, typically, charged residues, and P represents polar
(and, therefore, hydrophilic) residues. The positions of the heptad repeat are commonly denoted by the lowercase letters a through g.
These motifs are the basis for most coiled coil
s and, in particular, leucine zipper
s, which have predominantly leucine
in the d position of the heptad repeat.
Structural motif
In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a supersecondary structure, which appears also in a variety of other molecules...
that consists of a repeating pattern of seven amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s:
a b c d e f g
H P P H C P C
where H represents hydrophobic residues, C represents, typically, charged residues, and P represents polar
Chemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
(and, therefore, hydrophilic) residues. The positions of the heptad repeat are commonly denoted by the lowercase letters a through g.
These motifs are the basis for most coiled coil
Coiled coil
A coiled coil is a structural motif in proteins, in which 2-7 alpha-helices are coiled together like the strands of a rope . Many coiled coil type proteins are involved in important biological functions such as the regulation of gene expression e.g. transcription factors...
s and, in particular, leucine zipper
Leucine zipper
A leucine zipper, aka leucine scissors, is a common three-dimensional structural motif in proteins. These motifs are usually found as part of a DNA-binding domain in various transcription factors, and are therefore involved in regulating gene expression...
s, which have predominantly leucine
Leucine
Leucine is a branched-chain α-amino acid with the chemical formula HO2CCHCH2CH2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins...
in the d position of the heptad repeat.