title: Quantitative understanding of pH- and salt-mediated conformational folding of histidine-containing, β-hairpin-like peptides, through single-molecule probing with protein nanopores.
abstract: Inter-amino acid residues electrostatic interactions contribute to the conformational stability of peptides and proteins, influence their folding pathways, and are critically important to a multitude of problems in biology including the onset of misfolding diseases. By varying the pH and ionic strength, the inter-amino acid residues electrostatic interactions of histidine-containing, β-hairpin-like peptides alter their folding behavior, and we studied this through quantifying, at the unimolecular level, the frequency, dwell-times of translocation events, and amplitude of blockades associated with interactions between such peptides and the α-hemolysin (α-HL) protein. Acidic buffers were shown to dramatically decrease the rate of peptide capture by the α-HL protein, through the interplay of enthalpic and entropic contributions brought about on the free energy barrier, which controls the peptides-α-HL association rate. We found that in acidic buffers, the amplitude of the blockage induced by an α-HL, β-barrel-residing peptide is smaller than the value seen at neutral pH, and this supports our interpretation of the pH-induced change in the conformation of the peptide, which behaves as a less-stable hairpin at acidic pH values that obstructs, to a lesser extent, the protein pore. This is also confirmed by the fact that the dissociation rate of such model peptide from the α-HL's β-barrel is higher at acidic, as compared to neutral, pH values. Experiments performed in low-salt buffers revealed the dramatic decrease of the peptide capture rate by the α-HL protein, most likely caused by the increase in the radius of counterions cloud around the peptide that hinders peptide partition into the α-barrel, and histidines protonation at low pH bolsters this effect. Reduced electrostatic screening in low-salt buffers, at neutral pH, leads to a decrease in peptides effective cross-sectional areas and an increase of their mobility inside the α-HL pore, due most likely to the chain stretching augmentation, via increased inter-residues electrostatic interactions.
authors: Department of Physics, Alexandru I. Cuza University , Iasi 700506, Romania.
authors: Loredana
authors: L
authors: Mereuta
authors: Alina
authors: A
authors: Asandei
authors: Chang Ho
authors: CH
authors: Seo
authors: Yoonkyung
authors: Y
authors: Park
authors: Tudor
authors: T
authors: Luchian
mesh_terms: D000595:Amino Acid Sequence; D055724:Electrophysiological Phenomena; D006460:Hemolysin Proteins / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry; D008969:Molecular Sequence Data; D058608:Nanopores; D009994:Osmolar Concentration; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012965:Sodium Chloride / Q000737:chemistry*
chemical_list: D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D010455:Peptides; D012965:Sodium Chloride; D006639:Histidine