heptad repeat

{{Refimprove|date=December 2009}}

The heptad repeat is an example of a structural motif that consists of a repeating pattern of seven amino acids:{{cite book |doi=10.1016/B978-0-323-50878-0.00019-7 |chapter=Self-Assembled Peptide and Protein Nanofibers for Biomedical Applications |title=Biomedical Applications of Functionalized Nanomaterials |year=2018 |last1=Seroski |first1=Dillon T. |last2=Hudalla |first2=Gregory A. |pages=569–598 |isbn=978-0-323-50878-0 }}

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 coils and, in particular, leucine zippers, which have predominantly leucine in the d position of the heptad repeat.{{cite journal |vauthors=Chambers P, Pringle CR, Easton AJ |title=Heptad repeat sequences are located adjacent to hydrophobic regions in several types of virus fusion glycoproteins |journal=The Journal of General Virology |volume=71 |issue=12 |pages=3075–80 |year=1990 |pmid=2177097 |doi=10.1099/0022-1317-71-12-3075 |doi-access=free }}

A conformational change in a heptad repeat in the SARS-CoV-2 spike protein facilitates entry of the virus into the host cell membrane.{{cite journal | vauthors = Jackson CB, Farzan M, Chen B, Choe H | title = Mechanisms of SARS-CoV-2 entry into cells | journal = Nature Reviews Molecular Cell Biology | volume = 23 | issue=1 | pages = 3–20 | date = 2022 | doi = 10.1038/s41580-021-00418-x | pmc = 8491763 | pmid = 34611326}}