Signature of n→π* interactions in α-helices

Protein Sci. 2011 Jun;20(6):1077-81. doi: 10.1002/pro.627. Epub 2011 Apr 26.


The oxygen of a peptide bond has two lone pairs of electrons. One of these lone pairs is poised to interact with the electron-deficient carbon of the subsequent peptide bond in the chain. Any partial covalency that results from this n→π* interaction should induce pyramidalization of the carbon (C'(i)) toward the oxygen (O(i-1)). We searched for such pyramidalization in 14 peptides that contain both α- and β-amino acid residues and that assume a helical structure. We found that the α-amino acid residues, which adopt the main chain dihedral angles of an α-helix, display dramatic pyramidalization but the β-amino acid residues do not. Thus, we conclude that O(i-1) and C'(i) are linked by a partial covalent bond in α-helices. This finding has important ramifications for the folding and conformational stability of α-helices in isolation and in proteins.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Electrons
  • Models, Molecular
  • Peptides / chemistry*
  • Protein Folding
  • Protein Stability
  • Protein Structure, Secondary
  • Proteins / chemistry


  • Peptides
  • Proteins