Editing Structural motif (section)

==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 [[Protein tandem repeats|tandem repeats]].

; [[Beta hairpin]]: Extremely common. Two [[antiparallel (biochemistry)|antiparallel]] beta strands connected by a tight turn of a few amino acids between them.
; [[Beta sheet#Greek key motif|Greek key]]: Four beta strands, three connected by hairpins, the fourth folded over the top.
; [[Omega loop]]: A loop in which the residues that make up the beginning and end of the loop are very close together.<ref>{{cite book |last1=Hettiarachchy |first1=Navam S |title=Food Proteins and Peptides: Chemistry, Functionality, Interactions, and Commercialization |date=2012 |publisher=CRC Press Taylor & Francis Group |isbn=9781420093421 |page=16 |url=https://books.google.com/books?id=WWfMBQAAQBAJ&q=omega+loop+A+loop+in+which+the+residues+that+make+up+the+beginning+and+end+of+the+loop+are+very+close+together&pg=PA16 |access-date=24 March 2021}}</ref>
; [[Basic-helix-loop-helix|Helix-loop-helix]]: Consists of [[Alpha helix|alpha helices]] 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.
; [[Helix-turn-helix]]: Two α helices joined by a short strand of amino acids and found in many proteins that regulate gene expression.<ref>{{cite book |last1=Dubey |first1=R C |title=Advanced Biotechnology |date=2014 |publisher=S Chand Publishing |isbn=978-8121942904 |page=505 |url=https://books.google.com/books?id=SKgrDAAAQBAJ&q=Helix-turn-helix+Two+%CE%B1+helices+joined+by+a+short+strand+of+amino+acids+and+found+in+many+proteins+that+regulate+gene+expression&pg=PA505 |access-date=24 March 2021}}</ref>
; [[Nest (protein structural motif)|Nest]]: Extremely common. Three consecutive amino acid residues form an anion-binding concavity.<ref>{{cite journal |last1=Milner-White |first1=E. James |title=Functional Capabilities of the Earliest Peptides and the Emergence of Life |journal=Genes |date=September 26, 2011 |volume=2 |issue=4 |page=674 |doi=10.3390/genes2040671 |pmid=24710286 |pmc=3927598 |doi-access=free }}</ref>
; [[Niche (protein structural motif)|Niche]]: Extremely common. Three or four consecutive amino acid residues form a cation-binding feature.<ref>{{cite journal |last1=Milner-White |first1=E. James |title=Functional Capabilities of the Earliest Peptides and the Emergence of Life |journal=Genes |date=September 26, 2011 |volume=2 |issue=4 |page=678 |doi=10.3390/genes2040671 |pmid=24710286 |pmc=3927598 |doi-access=free }}</ref>