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. 2015 Jul 23;119(29):9084-90.
doi: 10.1021/jp508813n. Epub 2014 Nov 6.

Role of Charge and Solvation in the Structure and Dynamics of Alanine-Rich Peptide AKA2 in AOT Reverse Micelles

Anna Victoria Martinez  1 , Edyta Małolepsza  1 , Laura Domínguez  1 , Qing Lu  2 , John E Straub  1
Affiliations

Role of Charge and Solvation in the Structure and Dynamics of Alanine-Rich Peptide AKA2 in AOT Reverse Micelles

Anna Victoria Martinez et al. J Phys Chem B. .

Abstract

The propensity of peptides to form α-helices has been intensely studied using theory, computation, and experiment. Important model peptides for the study of the coil-to-helix transition have been alanine-lysine (AKA) peptides in which the lysine residues are placed on opposite sides of the helix avoiding charge repulsion while enhancing solubility. In this study, the effects of capped versus zwitterionic peptide termini on the secondary structure of alanine-rich peptides in reverse micelles are explored. The reverse micelles are found to undergo substantial shape fluctuations, a property observed in previous studies of AOT reverse micelles in the absence of solvated peptide. The peptides are observed to interact with water, as well as the AOT surfactant, including interactions between the nonpolar residues and the aliphatic surfactant tails. Computation of IR spectra for the amide I band of the peptide allows for direct comparison with experimental spectra. The results demonstrate that capped AKA2 peptides form more stable α helices than zwitterionic AKA2 peptides in reverse micelles. The rotational anisotropy decay of water is found to be distinctly different in the presence or absence of peptide within the reverse micelle, suggesting that the introduction of peptide significantly alters the number of free waters within the reverse micelle nanopool. However, neither the nature of the peptide termini (capped or charged) nor the degree of peptide helicity is found to significantly alter the balance of interactions between the peptides and the environment. Observed changes in the degree of helicity in AKA2 peptides in bulk solution and in reverse micelle environments result from changes in peptide confinement and hydration as well as direct nonpolar and polar interactions with the water-surfactant interface.

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Figures

Figure 1
Figure 1
CHARMM unrestrained reverse micelles with capped (left) AKA2 and zwitterionic (right) AKA2 peptides. The components of the RM are colored as follows: AOT tail groups, white surface; sulfonate head groups, yellow and red; sodium ions, dark green; water molecules, blue; peptide, bright green.
Figure 2
Figure 2
Secondary structure progression with respect to time of AKA2 peptides in unrestrained (top) and spherically restrained (bottom) reverse micelles for the CHARMM systems: capped AKA2 (left) and zwitterionic AKA2 (right). The secondary structure is indicated as helix (blue), turn (yellow), and coil (white).
Figure 3
Figure 3
Distribution of the peptide backbone RMSD for the last 30 ns of simulation for the AKA2 peptides in RMs for the CHARMM systems. Data are shown for capped/zwitterionic peptides in restrained (blue/yellow) and unrestrained (pink/green) RMs. Fluctuations of the capped peptides are substantially smaller than for the zwitterionic peptides.
Figure 4
Figure 4
Average number of AOT tail groups (top) and water molecules (bottom) within 4 Å of each AKA2 residue in the CHARMM RMs. Data are shown for capped/zwitterionic peptides in restrained (blue/yellow) and unrestrained (pink/green) RMs.
Figure 5
Figure 5
Number of AOT tail groups within 4 Å of AKA2 peptides. Peptides in the unrestrained RMs have more contact with the tail groups than peptides in the restrained RMs. Data are shown for capped/zwitterionic peptides in restrained (blue/yellow) and unrestrained (pink/green) RMs.
Figure 6
Figure 6
Number of water molecules within 4 Å of AKA2 peptides. Data are shown for capped/zwitterionic peptides in restrained (blue/yellow) and unrestrained (pink/green) RMs. The level of hydration of the peptides is similar in each environment with peptides in the restrained RMs being more hydrated than peptides in the unrestrained RMs.
Figure 7
Figure 7
Capped AKA2 in a restrained (left) and unrestrained (right) RM. The snapshot on the left shows the peptide in pink, and the snapshot on the right shows the peptide in green. Each peptide is shown with the surrounding water molecules in blue and AOT tails groups in gray.
Figure 8
Figure 8
Calculated IR spectra for capped and zwitterionic AKA2 peptides in restrained and unrestrained reverse micelles, with w0 = 6 at room temperature, compared with experiment.
Figure 9
Figure 9
Comparison of histograms of FFs of each peptide bond (low lying histograms), sum of FFs (green lines), and the calculated spectrum (orange lines) for each studied system. Red-shifted FFs are shown as thin lines, and blue-shifted FFs are shown as dotted lines. FFs were scaled by three for clarity.
Figure 10
Figure 10
Rotational anisotropy decay autocorrelation functions for restrained and unrestrained RMs with capped AKA2 peptide, AKA2 peptide in a zwitterionic form, and RMs without peptide.
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References

    1. Mukherjee S.; Chowdhury P.; Gai F. J. Phys. Chem. B 2006, 110, 11615. - PubMed
    1. Mukherjee S.; Chowdhury P.; Gai F. J. Phys. Chem. B 2009, 113, 531. - PMC - PubMed
    1. Chowdhary J.; Ladanyi B. M. J. Phys. Chem. B 2009, 113, 15029. - PubMed
    1. Levinger N. E. Science 2002, 298, 1722. - PubMed
    1. Hauser H.; Haering G.; Pande A.; Luisi P. J. Phys. Chem. 1989, 93, 7869.

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