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The Conformation and Aggregation of Proline-Rich Surfactant-Like Peptides

DOI: 10.1021/acs.jpcb.7b11463 DOI Help

Authors: Ian W. Hamley (University of Reading) , Valeria Castelletto (University of Reading) , Ashkan Dehsorkhi (University of Reading) , Juan Torras (Universitat Politècnica de Catalunya) , Carlos Aleman (Universitat Politècnica de Catalunya) , Irina Portnaya (Russell Berrie Nanotechnology Institute) , Dganit Danino (Russell Berrie Nanotechnology Institute)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Journal Of Physical Chemistry B

State: Published (Approved)
Published: February 2018
Diamond Proposal Number(s): 1606 , 1869

Abstract: The secondary structure of proline-rich surfactant-like peptides is examined for the first time and is found to be influenced by charged end groups in peptides P6K, P6E, and KP6E and an equimolar mixture of P6K and P6E. The peptides exhibit a conformational transition from unordered to polyproline II (PPII) above a critical concentration, detected from circular dichroism (CD) measurements and unexpectedly from fluorescence dye probe measurements. Isothermal titration calorimetry (ITC) measurements provided the Gibbs energies of hydration of P6K and P6E, which correspond essentially to the hydration energies of the terminal charged residues. A detailed analysis of peptide conformation for these peptides was performed using density functional theory calculations, and this was used as a basis for hybrid quantum mechanics/molecular mechanics molecular dynamics (QM/MM MD) simulations. Quantum mechanics simulations in implicit water show both peptides (and their 1:1 mixture) exhibit PPII conformations. However, hybrid QM/MM MD simulations suggest that some deviations from this conformation are present for P6K and P6E in peptide bonds close to the charged residue, whereas in the 1:1 mixture a PPII structure is observed. Finally, aggregation of the peptides was investigated using replica exchange molecular dynamics simulations. These reveal a tendency for the average aggregate size (as measured by the radius of gyration) to increase with increasing temperature, which is especially marked for P6K, although the fraction of the most populated clusters is larger for P6E.

Subject Areas: Chemistry

Instruments: B21-High Throughput SAXS , B23-Circular Dichroism

Other Facilities: ESRF