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Secondary structure effects on internal proton transfer in poly-peptides.

M Bouakil1, F Chirot2, M Girod2

  • 1Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, F-69622 Lyon, France.

Structural Dynamics (Melville, N.Y.)
|April 2, 2020
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Summary
This summary is machine-generated.

Proton transfer (PT) rates in peptide radical cations reveal peptide dynamics. A stable helix in HA6W peptides significantly slows PT, demonstrating competition between helix formation and proton transfer.

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Area of Science:

  • Chemical Physics
  • Biophysical Chemistry
  • Molecular Dynamics

Background:

  • Proton transfer (PT) is crucial in biological systems.
  • Understanding PT rates in peptides provides insights into their conformational dynamics.
  • Gas-phase basicity differences drive PT between amino acid residues.

Purpose of the Study:

  • To determine internal proton transfer rates in poly-peptide radical cations.
  • To investigate the influence of peptide conformation on PT rates.
  • To explore the interplay between gas-phase basicity and conformational dynamics.

Main Methods:

  • Utilized a pump-probe approach to measure PT rates.
  • Analyzed peptide radical cations containing histidine and tryptophan.
  • Examined conformational dynamics in poly-glycine, poly-proline, and poly-alanine peptides.

Main Results:

  • Histidine consistently pulls protons from tryptophan due to lower gas-phase basicity.
  • PT rate is limited by peptide conformational dynamics and residue proximity.
  • PT rates decrease with size in unstructured peptides.
  • A dramatic decrease in PT rates was observed for HA6W peptides, linked to helix formation.
  • Helix formation in HA6W competes with PT, slowing the process.

Conclusions:

  • Peptide conformation significantly impacts proton transfer rates.
  • Helix formation can dramatically reduce PT rates by limiting conformational flexibility.
  • Gas-phase basicity and helix propensity compete for charge localization in HA6W peptides.