Skip to main content
Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1985 Apr;82(8):2349–2353. doi: 10.1073/pnas.82.8.2349

Nature of the charged-group effect on the stability of the C-peptide helix.

K R Shoemaker, P S Kim, D N Brems, S Marqusee, E J York, I M Chaiken, J M Stewart, R L Baldwin
PMCID: PMC397555  PMID: 3857585

Abstract

The residues responsible for the pH-dependent stability of the helix formed by the isolated C-peptide (residues 1-13 of ribonuclease A) have been identified by chemical synthesis of analogues and measurement of their helix-forming properties. Each of the residues ionizing between pH 2 and pH 8 has been replaced separately by an uncharged residue. Protonation of Glu-2- is responsible for the sharp decrease in helix stability between pH 5 and pH 2, and deprotonation of His-12+ causes a similar decrease between pH 5 and pH 8. Glu-9- is not needed for helix stability. The results cannot be explained by the Zimm-Bragg model and host-guest data for alpha-helix formation, which predict that the stability of the C-peptide helix should increase when Glu-2- is protonated or when His-12+ is deprotonated. Moreover, histidine+ is a strong helix-breaker in host-guest studies. In proteins, acidic and basic residues tend to occur at opposite ends of alpha-helices: acidic residues occur preferentially near the NH2-terminal end and basic residues near the COOH-terminal end. A possible explanation, based on a helix dipole model, has been given [Blagdon, D. E. & Goodman, M. (1975) Biopolymers 14, 241-245]. Our results are consistent with the helix dipole model and they support the suggestion that the distribution of charged residues in protein helices reflects the helix-stabilizing propensity of those residues. Because Glu-9 is not needed for helix stability, a possible Glu-9-...His-12+ salt bridge does not contribute significantly to helix stability. The role of a possible Glu-2-...Arg-10+ salt bridge has not yet been evaluated. A charged-group effect on alpha-helix stability in water has also been observed in a different peptide system [Ihara, S., Ooi, T. & Takahashi, S. (1982) Biopolymers 21, 131-145]: block copolymers containing (Ala)20 and (Glu)20 show partial helix formation at low temperatures, pH 7.5, where the glutamic acid residues are ionized. (Glu)20(Ala)20Phe forms a helix that is markedly more stable than (Ala)20(Glu)20Phe. The results are consistent with a helix dipole model.

Full text

PDF
2349

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Bierzynski A., Kim P. S., Baldwin R. L. A salt bridge stabilizes the helix formed by isolated C-peptide of RNase A. Proc Natl Acad Sci U S A. 1982 Apr;79(8):2470–2474. doi: 10.1073/pnas.79.8.2470. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Blagdon D. E., Goodman M. Letter: Mechanisms of protein and polypeptide helix initiation. Biopolymers. 1975 Jan;14(1):241–245. doi: 10.1002/bip.1975.360140118. [DOI] [PubMed] [Google Scholar]
  3. Brown J. E., Klee W. A. Helix-coil transition of the isolated amino terminus of ribonuclease. Biochemistry. 1971 Feb 2;10(3):470–476. doi: 10.1021/bi00779a019. [DOI] [PubMed] [Google Scholar]
  4. Chou P. Y., Fasman G. D. Conformational parameters for amino acids in helical, beta-sheet, and random coil regions calculated from proteins. Biochemistry. 1974 Jan 15;13(2):211–222. doi: 10.1021/bi00699a001. [DOI] [PubMed] [Google Scholar]
  5. Dunn B. M., Chaiken I. M. Relationship between alpha-helical propensity and formation of the ribonuclease-S complex. J Mol Biol. 1975 Jul 15;95(4):497–511. doi: 10.1016/0022-2836(75)90313-7. [DOI] [PubMed] [Google Scholar]
  6. Hol W. G., Halie L. M., Sander C. Dipoles of the alpha-helix and beta-sheet: their role in protein folding. Nature. 1981 Dec 10;294(5841):532–536. doi: 10.1038/294532a0. [DOI] [PubMed] [Google Scholar]
  7. Hol W. G., van Duijnen P. T., Berendsen H. J. The alpha-helix dipole and the properties of proteins. Nature. 1978 Jun 8;273(5662):443–446. doi: 10.1038/273443a0. [DOI] [PubMed] [Google Scholar]
  8. Kim P. S., Baldwin R. L. A helix stop signal in the isolated S-peptide of ribonuclease A. 1984 Jan 26-Feb 1Nature. 307(5949):329–334. doi: 10.1038/307329a0. [DOI] [PubMed] [Google Scholar]
  9. Kim P. S., Bierzynski A., Baldwin R. L. A competing salt-bridge suppresses helix formation by the isolated C-peptide carboxylate of ribonuclease A. J Mol Biol. 1982 Nov 25;162(1):187–199. doi: 10.1016/0022-2836(82)90168-1. [DOI] [PubMed] [Google Scholar]
  10. Kuwajima K., Baldwin R. L. Nature and locations of the most slowly exchanging peptide NH protons in residues 1 to 19 of ribonuclease S. J Mol Biol. 1983 Sep 5;169(1):281–297. doi: 10.1016/s0022-2836(83)80184-3. [DOI] [PubMed] [Google Scholar]
  11. POTTS J. T., Jr, YOUNG D. M., ANFINSEN C. B. Reconstitution of fully active RNase S by carboxypeptidase-degraded RNase S-peptide. J Biol Chem. 1963 Jul;238:2593–2594. [PubMed] [Google Scholar]
  12. Rico M., Gallego E., Santoro J., Bermejo F. J., Nieto J. L., Herranz J. On the fundamental role of the Glu 2- ... Arg 10+ salt bridge in the folding of isolated ribonuclease A S-peptide. Biochem Biophys Res Commun. 1984 Sep 17;123(2):757–763. doi: 10.1016/0006-291x(84)90294-8. [DOI] [PubMed] [Google Scholar]
  13. Rico M., Nieto J. L., Santoro J., Bermejo F. J., Herranz J., Gallego E. Low-temperature 1H-NMR evidence of the folding of isolated ribonuclease S-peptide. FEBS Lett. 1983 Oct 17;162(2):314–319. doi: 10.1016/0014-5793(83)80779-0. [DOI] [PubMed] [Google Scholar]
  14. Rogers N. K., Sternberg M. J. Electrostatic interactions in globular proteins. Different dielectric models applied to the packing of alpha-helices. J Mol Biol. 1984 Apr 15;174(3):527–542. doi: 10.1016/0022-2836(84)90334-6. [DOI] [PubMed] [Google Scholar]
  15. Sheridan R. P., Levy R. M., Salemme F. R. alpha-Helix dipole model and electrostatic stabilization of 4-alpha-helical proteins. Proc Natl Acad Sci U S A. 1982 Aug;79(15):4545–4549. doi: 10.1073/pnas.79.15.4545. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Wada A. The alpha-helix as an electric macro-dipole. Adv Biophys. 1976:1–63. [PubMed] [Google Scholar]

Articles from Proceedings of the National Academy of Sciences of the United States of America are provided here courtesy of National Academy of Sciences

RESOURCES