IBMM, CNRS, ENSCM, University of Montpellier, 34095 Montpellier, France.
J Am Soc Mass Spectrom. 2020 Nov 4;31(11):2328-2337. doi: 10.1021/jasms.0c00269. Epub 2020 Oct 16.
As part of the sequencing issue, new approaches have to be found to sequence small natural peptides (<15-20 residues), which often present amino acid compositions, inducing merely singly charged species, that are quite difficult to thoroughly fragment under low-energy activation conditions in MS/MS experiments. Cationization by alkali metals, like Na, followed by collision-induced dissociations (CID) or the postsource metastable decay (PSD) of such cationized molecular ions was found to improve the sequence coverage of native peptides through the formation of [b + Na + OH] ions issued from C-terminal residue exclusion. Concerned by the identification of peptides with a C-terminal amide, the fragmentation pattern of their sodiated molecular ions was investigated. In contrast to the peptides featuring unmodified C-termini, the C-terminal loss did not occur, with the amide function triggering different fragmentation pathways. However, several residues, such as aspartic acid (D), glutamic acid (E), and arginine (R), influenced the dissociation of fixed-charge sodiated ions similarly to protonated peptides; more surprisingly, serine (S), threonine (T), and tyrosine (Y), which exhibit a hydroxyl function on their side chains, showed a very peculiar behavior that could help peptide sequencing.
作为测序问题的一部分，必须找到新的方法来对小于 15-20 个残基的小天然肽进行测序，这些肽通常具有氨基酸组成，只诱导单电荷物种，在 MS/MS 实验中，在低能量激活条件下很难彻底碎裂。发现通过碱金属（如 Na）的阳离子化，然后进行碰撞诱导解离（CID）或这种阳离子化分子离子的源后亚稳衰变（PSD），可以通过形成从 C 末端残基排除的 [b + Na + OH] 离子来提高天然肽的测序覆盖率。由于涉及到鉴定具有 C 末端酰胺的肽，因此研究了它们的加钠离子分子离子的碎裂模式。与未修饰 C 末端的肽相比，C 末端的丢失不会发生，酰胺官能团触发了不同的碎裂途径。然而，一些残基，如天冬氨酸（D）、谷氨酸（E）和精氨酸（R），与质子化肽类似，影响固定电荷加钠离子的解离；更令人惊讶的是，丝氨酸（S）、苏氨酸（T）和酪氨酸（Y），它们的侧链上具有羟基官能团，表现出非常特殊的行为，这可能有助于肽测序。
