title: Gas-phase helical peptides mimic solution-phase behavior.
abstract: In solution, α-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's C-terminal oxazolone ring to the N-terminus.
authors.affiliation: Ohio State University , 484 West 12th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Lindsay J
authors.initials: LJ
authors.lastname: Morrison
authors.forename: Vicki H
authors.initials: VH
authors.lastname: Wysocki
mesh_terms: D005740:Gases; D056004:Molecular Dynamics Simulation; D010455:Peptides / Q000737:chemistry*; D055550:Protein Stability; D017433:Protein Structure, Secondary; D012996:Solutions
chemical_list: D005740:Gases; D010455:Peptides; D012996:Solutions