Influence of a gamma amino acid on the structures and reactivity of peptide a₃ ions

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• 作者：Matthew C. Bernier^a ; Bela Paizs^a ; ^b ; ^{B.Paizs@dkfz.de} ; Vicki H. Wysocki^a ; ^{vwysocki@email.arizona.edu}
• 关键词：Peptides ; Collision induced dissociation ; Fragmentation ; Density functional theory ; Relative energies
• 刊名：International Journal of Mass Spectrometry
• 出版年：2012
• 期刊代码：43_13873806
• 类别：ch
• 出版时间：15 April, 2012
• 卷：316-318
• 期：Complete
• 页码：259-267
• 文件大小：1055 K

摘要

Collision-induced dissociation of protonated AGabaAIG (where Gaba is gamma-amino butyric acid, NH₂-(CH₂)₃-COOH) leads to an unusually stable a₃ ion. Tandem mass spectrometry and theory are used here to probe the enhanced stability of this fragment, whose counterpart is not usually observed in CID of protonated peptides containing only alpha amino acids. Experiments are carried out on the unlabelled and ¹⁵N-Ala labeled AGabaAIG (labeled separately at residue one or three) probing the b₃, a₃, a₃-NH₃ (a₃^*), and b₂ fragments while theory is used to characterize the most stable b₃, a₃, and b₂ structures and the formation and dissociation of the a₃ ion. Our results indicate the AGabaA oxazolone b₃ isomer undergoes head-to-tail macrocyclization and subsequent ring opening to form the GabaAA sequence isomer while this chemistry is energetically disfavored for the AAA sequence. The AGabaA a₃ fragment also undergoes macrocyclization and rearrangement to form the rearranged imine-amide isomer while this reaction is energetically disfavored for the AAA sequence. The barriers to dissociation of the AGabaA a₃ ion via the a₃ 鈫?#xA0;b₂ and a₃ 鈫?#xA0;a₃^* channels are higher than the literature values reported for the AAA sequence. These two effects provide a clear explanation for the enhanced stability of the AGabaA a₃ ion.