C cap

The term C cap (C-cap, Ccap) describes an amino acid in a particular position within a protein or polypeptide. [1] [2] [3] [4] [5] [6] The C cap residue of an alpha helix is the last amino acid residue at the C terminus of the helix. More precisely, it is defined as the last residue (i) whose NH group is hydrogen-bonded to the CO group of residue i-4 (or sometimes residue i-3). Because of this it is sometimes also described as the residue following the helix.

Certain motifs occur commonly at or around the C cap, notably the Schellman loop and the niche (protein structural motif).

The N cap is the corresponding amino acid residue at the other end of the helix


References

  1. ↑ Richardson, JM; Richardson DC (1988). "Amino acid preferences for specific locations at the ends of alpha-helices". Science 240: 1648–1652. doi:10.1126/science.3381086.
  2. ↑ Presta, LG; Rose GD (1988). "Helix Caps". Science 240: 1632–1641. doi:10.1126/science.2837824. PMID 2837824.
  3. ↑ Doig, AJ; MacArthur MW (1997). "Structures of N-termini of helices in proteins". Protein Science 6: 147–155. doi:10.1002/pro.5560060117. PMC 2143508. PMID 9007987.
  4. ↑ Aurora, R; Rose GD (1998). "Helix Capping". Protein Science 7: 21–38. doi:10.1002/pro.5560070103. PMC 2143812. PMID 9514257.
  5. ↑ Gunasekaran, K; Nagarajam HA (1998). "Sterochemical punctuation marks in protein structure". Journal of Molecular Biology 275: 917–932. doi:10.1006/jmbi.1997.1505. PMID 9480777.
  6. ↑ Leader, DP; Milner-White EJ (2011). "The structure of the ends of helices in globular proteins". Proteins 79: 1010–1019. doi:10.1002/prot.22942.
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