AP helical stability in salt solutions

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

Pittsburgh

Conferencia; 2009 APS March Meeting; 2009

American Physical Society

Protein dynamics depends on the environment and the inclusion ofsalts in the simulation of folding/unfolding becomes extremely necessary when comparing energy barriers or reaction rates with experimentalresults. The aim of this study is to investigate the effects of three sodiumsalts: NaClO4,NaCl and Na2SO4 on the helical stability of AP,a mainly alanine peptide. The dependence of the peptide helical stability on the environment has been studiedusing Replica Exchange Molecular Dynamics (REMD) simulations, CircularDichroism (CD) and Ultraviolet Raman Resonance Spectroscopy (UVRS)experiments. It was found that NaClO4 solution strongly stabilizes the helicalstates and that the order in which sodium salts stabilize the peptidehelical states follows a reverse Hofmeister Series (ClO−4<Cl−<SO2−4). Another interesting result found is that ClO−4ions are attracted to the backbone; Cl− ions are repelledwhile SO2−4 ions are attracted to the positive side chains.A thorough investigation of the ion effects on the first andsecond solvation water along with the Kirkwood-Buff theory forsolutions allowed us to explain the physical mechanisms involvedin the observed ion specific effects.