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Complex ion effects on polypeptide conformational stability: chloride and sulfate salts of guanidinium and tetrapropylammonium.

Authors
Type
Published Article
Journal
Journal of the American Chemical Society
0002-7863
Publisher
American Chemical Society
Publication Date
Volume
133
Issue
19
Pages
7300–7303
Identifiers
DOI: 10.1021/ja201349g
PMID: 21520945
Source
Medline

Abstract

The effects of chloride and sulfate salts of tetrapropylammonium (TPA(+)) and guanidinium (Gdm(+)) on the conformational stabilities of tryptophan zipper (trpzip) and α-helical (alahel) peptides were measured by circular dichroism spectroscopy. Like Gdm(+), TPA(+) interacts with the planar tryptophan indole group, perturbing the conformational stability of trpzip peptides. TPA(+) effects are largely unaffected by sulfate, indicating an absence of the heteroion pairing that is observed in concentrated Gdm(2)SO(4) solutions. TPA(+) stabilizes helical conformations in alahel peptides, indicating exclusion from the peptide bond. The observations are broadly consistent with predictions of molecular dynamics simulations [Mason, P. E.; et al. J. Phys. Chem. B2009, 113, 3227-3234], indicating that the effects of complex ions on proteins are increasingly predictable in terms of ion hydration, complementary interactions with specific protein groups, and ion-pairing contributions.

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