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Effects of terminal functional groups on the stability of the polyproline II structure : a combined experimental and theoretical study

Kuemin, Michael and Schweizer, Sabine and Ochsenfeld, Christian and Wennemers, Helma. (2009) Effects of terminal functional groups on the stability of the polyproline II structure : a combined experimental and theoretical study. Journal of the American Chemical Society, Vol. 131, H. 42 , S. 15474–15482.

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Official URL: http://edoc.unibas.ch/dok/A5262568

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Abstract

The conformational stability of the polyproline II (PPII) helix with respect to the functional groups at the C- and N-termini was examined both experimentally and theoretically. Oligoprolines AcN-[Pro]12- CONH2 (1), HN-[Pro]12-CONH2 (2), AcN-[Pro]12-CO2H (3), and HN-[Pro]12-CO2H (4) with charged and capped termini served as model compounds, and the relative ease with which they switch from the PPII to the polyproline I (PPI) helix was used as a measure to analyze their conformational stabilities. CD spectroscopic studies demonstrate that a positively charged N-terminus and a negatively charged C-terminus destabilize the PPII helix and favor the PPI helix, whereas capped termini favor the PPII over the PPI helix. These experimental findings are supported by the energy differences between the PPII and PPI helices of oligoprolines 1-4 computed by ab initio methods including electron-correlation effects (second- order Møller-Plesset perturbation theory, MP2). Furthermore, these quantum-chemical calculations show that differences in charge-dipole interactions are responsible for the experimentally and computationally observed relative stabilities. Although these electrostatic interactions between the terminal charges and the amide dipoles stabilize both helices, they are significantly stronger in the PPI helix where the amide bonds are oriented almost linear to the helix axis as compared to the PPII helix in which the amides are nearly perpendicular to the axis. Moreover, we demonstrate that a negative charge at the C-terminus has a more pronounced effect on the relative stability as compared to a positive charge at the N-terminus due to destabilization of the PPII helix by repulsive interaction between the C-terminal carboxylate with the neighboring amide bond. Studies at different pH values verified the electrostatic nature of the observed effects and demonstrate how changes in the protonation state can be used to deliberately stabilize the PPII helix over the PPI helix or vice versa.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Former Organization Units Chemistry > Bioorganische Chemie (Wennemers)
UniBasel Contributors:Wennemers, Helma
Item Type:Article, refereed
Article Subtype:Research Article
Bibsysno:Link to catalogue
Publisher:American Chemical Society
ISSN:0002-7863
Note:Publication type according to Uni Basel Research Database: Journal article
Last Modified:22 Mar 2012 14:29
Deposited On:22 Mar 2012 14:07

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