title: Impact of ion binding on poly-L-lysine (un)folding energy landscape and kinetics.
abstract: We utilize T-jump UV resonance Raman spectroscopy (UVRR) to study the impact of ion binding on the equilibrium energy landscape and on (un)folding kinetics of poly-L-lysine (PLL). We observe that the relaxation rates of the folded conformations (including π-helix (bulge), pure α-helix, and turns) of PLL are slower than those of short alanine-based peptides. The PLL pure α-helix folding time is similar to that of short alanine-based peptides. We for the first time have directly observed that turn conformations are α-helix and π-helix (bulge) unfolding intermediates. ClO(4)(-) binding to the Lys side chain -NH(3)(+) groups and the peptide backbone slows the α-helix unfolding rate compared to that in pure water, but little impacts the folding rate, resulting in an increased α-helix stability. ClO(4)(-) binding significantly increases the PLL unfolding activation barrier but little impacts the folding barrier. Thus, the PLL folding coordinate(s) differs from the unfolding coordinate(s). The-π helix (bulge) unfolding and folding coordinates do not directly go through the α-helix energy well. Our results clearly demonstrate that PLL (un)folding is not a two-state process.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: Kan
authors.initials: K
authors.lastname: Xiong
authors.forename: Sanford A
authors.initials: SA
authors.lastname: Asher
mesh_terms: D007477:Ions / Q000737:chemistry*; D007700:Kinetics; D010472:Perchlorates / Q000737:chemistry; D011107:Polylysine / Q000737:chemistry / Q000378:metabolism*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017670:Sodium Compounds / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D010472:Perchlorates; D017670:Sodium Compounds; D014867:Water; D011107:Polylysine; C031068:sodium perchlorate