Salt dependence of an alpha helical peptide folding energy landscapes

KAN XIONG; ELIANA K. ASCIUTTO; JEFFRY D. MADURA; SANFORD A. ASHER

BIOCHEMISTRY

AMER CHEMICAL SOC

Año: 2009 vol. 48 p. 10818 - 10826

0006-2960

AbstractWe 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 alpha-helical peptide, AP of sequence AAAAA-(AAARA)3A. NaClO4 stabilizes alpha-helical-like conformations more than does NaCl, which stabilizes more than Na2SO4 at identical ionic strengths. This alpha-helix stabilization ordering is the reverse of the Hofmeister series of anions in their ability to disorder water hydrogen bonding. Much of the NaClO4 alpha-helix stabilization results from ClO4- association with the AP terminal -NH3þ groups and Arg side chains. ClO4- stabilizes 310-helix conformations but destabilizes turn conformations. The decreased Cl- and SO42- AP alpha-helix stabilization probably results from a decreased association with the Arg and terminal -NH3þ groups. Cl-is expected to have a smaller binding affinity and thus stabilizes alpha-helical conformations intermediately between NaClO4 and Na2SO4. Electrostatic screening stabilizes π-bulge conformations.