Gas-Phase Helical Peptides Mimic Solution-Phase Behavior
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- 作者：Lindsay J. Morrison ; Vicki H. Wysocki
- 刊名：Journal of the American Chemical Society
- 出版年：2014
- 出版时间：October 8, 2014
- 年：2014
- 卷：136
- 期：40
- 页码：14173-14183
- 全文大小：562K
- ISSN：1520-5126
文摘
In solution, 伪-helices are stabilized at the termini by a variety of different capping interactions. Study of these interactions in the gas phase provides a unique means to explore the intrinsic properties that cause this stabilization. Evidence of helical and globular conformations is presented here for gas-phase, doubly charged peptides of sequence XAnK, wherein X is D, N, Q, or L. The relative abundance of the helical conformation is found to vary as a function of peptide length and the identity of the first amino acid, consistent with solution phase studies that have looked at the identity of the first amino acid. The N-terminal, b ion fragments of the doubly charged precursor peptides are shown to form helical and globular conformations. The stability of the helical fragments is examined as a function of fragment length, N-terminal amino acid, precursor conformation, and the activation energy used to generate the fragment. At lower collision energies, helical b ions preferentially form, particularly from helical precursors. The abundance of the helical b ion population is observed to dramatically decrease for NAn and DAn b ions smaller than the b10; simulations suggest this feature is due to the b10 having two complete turns of the helix, while the b9 and smaller ions have only a partial second turn, suggesting the b10 is the lower limit for stable helical conformations in b ions. Use of higher collision energies promotes the formation of globular structures in the b ions. This characteristic is attributed to increased conformational dynamics and subsequently improved proton transfer kinetics from the b ion鈥檚 C-terminal oxazolone ring to the N-terminus.