The specific binding sites of Hofmeister ions with an uncharged 600 residue elastin-like polypeptide, 
(VPGVG)120, were elucidated using a combination of NMR and thermodynamic measurements along with 
molecular dynamic simulations. It was found that the large soft anions such as SCN- and I- interact 
with the polypeptide backbone via a hybrid binding site that consists of the amide nitrogen and the 
adjacent alpha-carbon. The hydrocarbon groups at these sites bear a slight positive charge, which 
enhances anion binding without disrupting specific hydrogen bonds to water molecules. The hydrophobic 
side chains do not contribute significantly to anion binding or the corresponding salting-in behavior 
of the biopolymer. Cl- binds far more weakly to the amide nitrogen/.-carbon binding site, while SO42- 
is repelled from both the backbone and hydrophobic side chains of the polypeptide. The Na+ counterions 
are also repelled from the polypeptide. The identification of these molecular-level binding sites 
provides new insights into the mechanism of peptide-anion interactions.