# N cap

> Mediated Wiki article. Canonical URL: https://mediated.wiki/source/N_cap
> Markdown URL: https://mediated.wiki/source/N_cap.md
> Source: https://en.wikipedia.org/wiki/N_cap
> Source revision: 1181811856
> License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/)

{{Short description|Amino acid}}
The term '''N cap''' (N-cap, Ncap) describes an [amino acid](/source/amino_acid) in a particular position within a [protein](/source/protein) or [polypeptide](/source/polypeptide).<ref>{{cite journal|last=Richardson|first=JM|author2=Richardson DC |title=Amino acid preferences for specific locations at the ends of alpha-helices|journal=Science|year=1988|volume=240|issue=4859|pages=1648–1652|doi= 10.1126/science.3381086|pmid=3381086|bibcode=1988Sci...240.1648R|s2cid=38467101}}</ref><ref>{{cite journal|last=Presta|first=LG|author2=Rose GD |title=Helix Caps|journal=Science|year=1988|volume=240|issue=4859|pages=1632–1641|doi= 10.1126/science.2837824|pmid=2837824|bibcode=1988Sci...240.1632P}}</ref><ref>{{cite journal|last=Doig|first=AJ|author2=MacArthur MW |title=Structures of N-termini of helices in proteins|journal=Protein Science|year=1997|volume=6|issue=1|pages=147–155|doi= 10.1002/pro.5560060117|pmid=9007987|pmc=2143508}}</ref><ref>{{cite journal|last=Aurora|first=R|author2=Rose GD |title=Helix Capping|journal=Protein Science|year=1998|volume=7|issue=1|pages=21–38|doi= 10.1002/pro.5560070103|pmid=9514257|pmc=2143812}}</ref><ref>{{cite journal|last=Gunasekaran|first=K|author2=Nagarajam HA |title=Stereochemical punctuation marks in protein structure|journal=Journal of Molecular Biology|year=1998|volume=275|issue=5|pages=917–932|doi= 10.1006/jmbi.1997.1505|pmid=9480777|url=http://repository.ias.ac.in/4151/1/320.pdf}}</ref><ref>{{cite journal|last=Leader|first=DP|author2=Milner-White EJ |title=The structure of the ends of helices in globular proteins|journal=Proteins|year=2011|volume=79|issue=3|pages=1010–1019|doi= 10.1002/prot.22942|pmid=21287629|s2cid=22240314}}</ref> The N cap residue of an [alpha helix](/source/alpha_helix) is the first [amino acid](/source/amino_acid) residue at the [N terminus](/source/N_terminus) of the helix. More precisely, it is defined as the first residue (i) whose CO group is [hydrogen-bond](/source/hydrogen-bond)ed to the NH group of residue i+4 (or sometimes residue i+3). Because of this it is sometimes also described as the residue prior to the helix.

Capping motifs are those often found at the N cap. [Asx turn](/source/Asx_turn)s, [ST turn](/source/ST_turn)s, and [asx motif](/source/asx_motif)s are often found at such situations, with the asx or [serine](/source/serine) or [threonine](/source/threonine) residue at the N cap.

The [C cap](/source/C_cap) is the corresponding amino acid residue at the other end of the helix

==References==
<references />

Category:Amino acids

---
Adapted from the Wikipedia article [N cap](https://en.wikipedia.org/wiki/N_cap) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/N_cap?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.