15871-56-4Relevant articles and documents
α-helical versus 310-helical conformation of alanine-based peptides in aqueous solution: An electron spin resonance investigation
Smythe, Mark L.,Nakaie, Clovis R.,Marshall, Garland R.
, p. 10555 - 10562 (2007/10/03)
Due to the difficulties in experimentally differentiating between the α- and 310-helical conformations in solution, isolated helical peptides have been assumed to be in the α-helical conformation. However, recent electron spin resonance (ESR) studies have suggested that such peptides, in particular short alanine-based peptides, are 310-helical (Miick, S. M.; et al. Nature 1992, 359, 653-5). This result prompted us to further investigate the helical conformations of alanine-based peptides in solution using electron spin resonance spectroscopy. Unlike previous investigations with a flexible link connecting the spin-label to the peptide backbone, we used a conformationally constrained spin-label (4-amino-4-carboxy-2,2,6,6-tetramethylpiperidine-1-oxyl, Toac) that is rigidly attached to the peptide backbone. From a combination of molecular modeling and ESR spectroscopy investigations, it was concluded that these alanine-based peptides exist primarily in the α-helical conformation, and not the 310-form as previously suggested for an analogous set of peptides in aqueous environments. This discrepancy is thought to be due to the differences in flexibility of the spin-labels employed. The conformationally constrained spin-label Toac used in this study should accurately reflect the backbone conformation. Free energy surfaces, or potentials of mean force, for the conformational transition of the spin-label used in previous studies (Miick S. M.; et al. Nature 1992, 359, 653-5) suggest that this spin-label is too flexible to accurately distinguish between the α- and 310-helical conformations.
