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

摘要

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 peptidesin reverse micelles. The rotational anisotropy decay of water is foundto be distinctly different in the presence or absence of peptide withinthe reverse micelle, suggesting that the introduction of peptide significantlyalters 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 alterthe balance of interactions between the peptides and the environment.Observed changes in the degree of helicity in AKA2 peptidesin bulk solution and in reverse micelle environments result from changesin peptide confinement and hydration as well as direct nonpolar andpolar interactions with the water–surfactant interface.