Identification of N-terminal helix capping boxes by means of 13C chemical shifts

J Biomol NMR. 1994 May;4(3):455-8. doi: 10.1007/BF00179351.


We have examined the 13C alpha and 13C beta chemical shifts of a number of proteins and found that their values at the N-terminal end of a helix provide a good predictor for the presence of a capping box. A capping box consists of a hydrogen-bonded cycle of four amino acids in which the side chain of the N-cap residue forms a hydrogen bond with the backbone amide of the N3 residue, whose side chain in turn may accept a hydrogen bond from the amide of the N-cap residue. The N-cap residue exhibits characteristic values for its backbone torsion angles, with phi and psi clustering around 94 +/- 15 degrees and 167 +/- 5 degrees, respectively. This is manifested by a 1-2 ppm upfield shift of the 13 C alpha resonance and a 1-4 ppm downfield shift of the 13C beta resonance, relative to their random coil values, and is mainly associated with the unusually large value of psi. The residues following the N-cap residue exhibit downfield shifts of 1-3 ppm for the 13C alpha resonances and small upfield shifts for the 13C beta ones, typical of an alpha-helix.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Calmodulin / chemistry
  • Carbon Isotopes
  • Cattle
  • Heterogeneous-Nuclear Ribonucleoproteins
  • Interleukin-4 / chemistry
  • Magnetic Resonance Spectroscopy / methods*
  • Molecular Sequence Data
  • Protein Structure, Secondary*
  • Proteins / chemistry*
  • RNA, Heterogeneous Nuclear
  • Ribonuclease H / chemistry
  • Ribonucleoproteins / chemistry
  • Trypsin Inhibitor, Kazal Pancreatic / chemistry


  • Calmodulin
  • Carbon Isotopes
  • Heterogeneous-Nuclear Ribonucleoproteins
  • Proteins
  • RNA, Heterogeneous Nuclear
  • Ribonucleoproteins
  • Interleukin-4
  • Trypsin Inhibitor, Kazal Pancreatic
  • Ribonuclease H