%0 Journal Article
%@ 0006-2960
%A Xiong, K
%A Asciutto, EK
%A Madura, JD
%A Asher, SA
%D 2009
%F pittir:17263
%J Biochemistry
%N 45
%P 10818 - 10826
%T Salt dependence of an α-helical peptide folding energy landscapes
%U http://d-scholarship-dev.library.pitt.edu/17263/
%V 48
%X We used CD,UV resonance Raman spectroscopy, and molecular dynamics simulation to examine the impact of salts on the conformational equilibria and the Ramachandran Ψ angle (un)folding Gibbs free energy landscape coordinate of a mainly polyalanine α-helical peptide, AP of sequence AAAAA-(AAARA)3A. NaClO4 stabilizes α-helical-like conformations more than does NaCl, which stabilizes more than Na 2SO4 at identical ionic strengths. This α-helix stabilization ordering is the reverse of the Hofmeister series of anions in their ability to disorder water hydrogen bonding. Much of the NaClO4 α-helix stabilization results from ClO4- association with the AP terminal-NH3+ groups and Arg side chains. ClO4- stabilizes 310-helix conformations but destabilizes turn conformations. The decreased Cl- and SO 42- AP α-helix stabilization probably results from a decreased association with the Arg and terminal -NH3+ groups. Cl- is expected to have a smaller binding affinity and thus stabilizes α-helical conformations intermediately between NaClO 4 and Na2SO4. Electrostatic screening stabilizes π-bulge conformations. © 2009 American Chemical Society.