Department of Chemistry and Biochemistry, The University of Arizona, 1306 East University Boulevard, P.O. Box 210041, Tucson, Arizona 85721-0041, USA.
J Phys Chem A. 2013 Feb 14;117(6):1291-8. doi: 10.1021/jp306759f. Epub 2013 Feb 6.
To probe the structural implications of the proline residue on its characteristic peptide fragmentation patterns, in particular its unusual cleavage at its C-terminus in formation of a b(2) ion in XxxProZzz sequences, the structures of a series of proline-containing b(2)(+) ions were studied by using action infrared multiphoton dissociation (IRMPD) spectroscopy and fragment ion hydrogen-deuterium exchange (HDX). Five different Xxx-Pro b(2)(+) ions were studied, with glycine, alanine, isoleucine, valine, or histidine in the N-terminal position. The residues selected feature different sizes, chain lengths, and gas phase basicities to explore whether the structure of the N-terminal residue influences the Xxx-Pro b(2)(+) ion structure. In proteins, the proline side chain-to-backbone attachment causes its peptide bonds to be in the cis conformation more than any other amino acid, although trans is still favored over cis. However, HP is the only b(2)(+) ion studied here that forms the diketopiperazine exclusively. The GP, AP, IP, and VP b(2)(+) ions formed from protonated tripeptide precursors predominantly featured oxazolone structures with small diketopiperazine contributions. In contrast to the b(2)(+) ions generated from tripeptides, synthetic cyclic dipeptides VP and HP were confirmed to have exclusive diketopiperazine structures.
为了探究脯氨酸残基对其特征肽片段化模式的结构影响，特别是在 XxxProZzz 序列中形成 b(2)离子时其 C 末端的异常裂解，我们通过使用动作红外多光子解离（IRMPD）光谱和片段离子氘代（HDX）研究了一系列含脯氨酸的 b(2)(+)离子的结构。研究了五种不同的 Xxx-Pro b(2)(+)离子，其中 N 末端为甘氨酸、丙氨酸、异亮氨酸、缬氨酸或组氨酸。选择的残基具有不同的大小、链长和气相碱性，以探究 N 末端残基的结构是否影响 Xxx-Pro b(2)(+)离子的结构。在蛋白质中，脯氨酸侧链与骨架的连接导致其肽键更倾向于顺式构象，尽管反式构象仍优先于顺式构象。然而，HP 是这里唯一研究的 b(2)(+)离子，它只形成二酮哌嗪。由质子化三肽前体生成的 GP、AP、IP 和 VP b(2)(+)离子主要具有噁唑啉结构，二酮哌嗪的贡献较小。与三肽生成的 b(2)(+)离子不同，合成的环状二肽 VP 和 HP 被确认为具有独特的二酮哌嗪结构。
