Non-classical helix-stabilizing interactions: C-H⋯O H-bonding between Phe and Glu side chains in α-helical peptides

Zhengshuang Shi, C. Anders Olson, Anthony J. Bell, Neville R. Kallenbach

Research output: Contribution to journalArticlepeer-review


The classical picture of H-bonds has evolved considerably. In contrast to earlier expectations, C-H⋯O H-bonds are now known to be prevalent in both small organic and large biological systems. However, there are few reports on the energetic contribution of C-H⋯O H-bonds in protein or polypeptide systems and we do not know whether such interactions are stabilizing. Here we investigate C-H⋯O H-bonding interactions between Phe and Glu side chains by determining their effects on the helicity of model α-helical peptides using a combination of CD and NMR spectroscopy. The results suggest that Glu/Phe C-H⋯O H-bonding interactions stabilize helical structure, but only in the orientation Glu→Phe (N→C). Each Glu→Phe (N→C) interaction can contribute approximately -0.5 kcal mol-1 to the stability of helical peptide. In the reverse orientation, Phe→Glu (N→C) appears to contribute negligibly. pH titrations provide further evidence for the existence of C-H⋯O H-bonds. The C-H⋯O H-bonding interactions in these peptides are insensitive to the screening effect of added neutral salt. Our results provide quantitative energetic information on C-H⋯O H-bonds that should be useful for empirical force-field calibration.

Original languageEnglish (US)
Pages (from-to)267-279
Number of pages13
JournalBiophysical Chemistry
Issue number102
StatePublished - Dec 10 2002


  • C-H⋯O H-bonds
  • Energetics
  • Free energy
  • α-Helix

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Organic Chemistry


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