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

Ian W. Hamley*, Valeria Castelletto, Ashkan Dehsorkhi, Juan Torras, Carlos Aleman, Irina Portnaya, Dganit Danino

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

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.

Original languageEnglish
Pages (from-to)1826-1835
Number of pages10
JournalJournal of Physical Chemistry B
Volume122
Issue number6
DOIs
StatePublished - 15 Feb 2018
Externally publishedYes

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