In a polymer biological molecule, such as a protein or nucleic acid, a structural motif is a common three-dimensional structure that appears in a variety of different, evolutionarily unrelated molecules.
In nucleic acids
Depending upon the sequence and other conditions, nucleic acids can form a variety of structural motifs which is thought to have biological significance.
- Cruciform DNA
- Cruciform DNA is a form of non-B DNA that requires at least a 6 nucleotide sequence of inverted repeats to form a structure consisting of a stem, branch point and loop in the shape of a cruciform, stabilized by negative DNA supercoiling.
In proteins
In proteins, a structural motif describes the connectivity between secondary structural elements. 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 often include loops of variable length and unspecified structure. Structural motifs may also appear as tandem repeats.
- Beta hairpin
- Extremely common. Two antiparallel beta strands connected by a tight turn of a few amino acids between them.
- Greek key
- Four beta strands, three connected by hairpins, the fourth folded over the top.
- Helix-loop-helix
- Consists of Alpha helix bound by a looping stretch of amino acids. This motif is seen in transcription factors.
- Zinc finger
- Two beta strands with an alpha helix end folded over to bind a zinc ion. Important in DNA binding proteins.
- Nest
- Extremely common. Three consecutive amino acid residues form an anion-binding concavity.
- Niche
- Extremely common. Three or four consecutive amino acid residues form a cation-binding feature.
See also
Further reading
