Department of Chemistry, University of the Pacific, Stockton, CA, U.S.A., USA.
The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, U.S.A., USA.
Biopolymers. 2020 Jul;111(7):e23358. doi: 10.1002/bip.23358. Epub 2020 Jun 12.
Peptoids belong to a class of sequence-controlled polymers comprising of N-alkylglycine. This study focuses on using tandem mass spectrometry techniques to characterize the fragmentation patterns of a set of singly and doubly protonated peptoids consisting of one basic residue placed at different positions. The singly protonated peptoids fragment by producing predominately high-abundant C-terminal ions called Y-ions and low-abundant N-terminal ions called B-ions. Computational studies suggest that the proton affinity (PA) of the C-terminal fragments is generally higher than that of the N-terminal fragments, and the PA of the former increases as the fragments are elongated. The B-ions are likely formed upon dissociating the proton-activated amide bonds via an oxazolone structure, and the Y-ions are produced subsequently by abstracting a proton from the newly formed B-ions, which is energetically favored. The doubly protonated peptoids prefer to fragment closest to either the N- or the C-terminus and produce corresponding B/Y-ion pairs. The basic residue seems to dictate the preferred fragmentation site, which may be the result of minimizing the repulsion between the two charges. Water and terminal neutral losses are a facile process accompanying the peptoid fragmentation in both charge states. The patterns appear to be highly influenced by the location of the basic residue.
肽缩氨酸属于一类序列可控聚合物，由 N-烷基甘氨酸组成。本研究侧重于使用串联质谱技术来表征一组由一个碱性残基放置在不同位置的单质子化和双质子化肽缩氨酸的碎裂模式。单质子化的肽缩氨酸通过产生主要的高丰度 C 末端离子（称为 Y-离子）和低丰度 N 末端离子（称为 B-离子）来进行片段化。计算研究表明，C 末端片段的质子亲和力（PA）通常高于 N 末端片段，并且前者的 PA 随着片段的延长而增加。B-离子可能是通过 oxazolone 结构解离质子化的酰胺键形成的，随后通过从新形成的 B-离子中提取质子形成 Y-离子，这在能量上是有利的。双质子化的肽缩氨酸优先在 N-或 C-末端附近进行片段化，并产生相应的 B/Y-离子对。碱性残基似乎决定了优先的片段化位点，这可能是由于两个电荷之间的排斥最小化的结果。在两种电荷状态下，水和末端中性损失是伴随着肽缩氨酸片段化的一种简单过程。这些模式似乎受到碱性残基位置的高度影响。
