title: Complex ion effects on polypeptide conformational stability: chloride and sulfate salts of guanidinium and tetrapropylammonium.
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.
authors.affiliation: School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK. c.dempsey@bris.ac.uk
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Dempsey
authors.forename: Philip E
authors.initials: PE
authors.lastname: Mason
authors.forename: Pavel
authors.initials: P
authors.lastname: Jungwirth
mesh_terms: D000595:Amino Acid Sequence; D002712:Chlorides / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D019791:Guanidine / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D055550:Protein Stability; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*
chemical_list: D002712:Chlorides; D056831:Coordination Complexes; D010455:Peptides; D000644:Quaternary Ammonium Compounds; D013431:Sulfates; C052377:tetrapropylammonium; D019791:Guanidine