Chemical Derivatization of Peptide Carboxyl Groups for Highly Efficient Electron Transfer Dissociation
作者:Brian L. Frey、Daniel T. Ladror、Samuel B. Sondalle、Casey J. Krusemark、April L. Jue、Joshua J. Coon、Lloyd M. Smith
DOI:10.1007/s13361-013-0701-2
日期:2013.11.1
The carboxyl groups of tryptic peptides were derivatized with a tertiary or quaternary amine labeling reagent to generate more highly charged peptide ions that fragment efficiently by electron transfer dissociation (ETD). All peptide carboxyl groups—aspartic and glutamic acid side-chains as well as C-termini—were derivatized with an average reaction efficiency of 99 %. This nearly complete labeling avoids making complex peptide mixtures even more complex because of partially-labeled products, and it allows the use of static modifications during database searching. Alkyl tertiary amines were found to be the optimal labeling reagent among the four types tested. Charge states are substantially higher for derivatized peptides: a modified tryptic digest of bovine serum albumin (BSA) generates ~90% of its precursor ions with z > 2, compared with less than 40 % for the unmodified sample. The increased charge density of modified peptide ions yields highly efficient ETD fragmentation, leading to many additional peptide identifications and higher sequence coverage (e.g., 70 % for modified versus only 43 % for unmodified BSA). The utility of this labeling strategy was demonstrated on a tryptic digest of ribosomal proteins isolated from yeast cells. Peptide derivatization of this sample produced an increase in the number of identified proteins, a >50 % increase in the sequence coverage of these proteins, and a doubling of the number of peptide spectral matches. This carboxyl derivatization strategy greatly improves proteome coverage obtained from ETD-MS/MS of tryptic digests, and we anticipate that it will also enhance identification and localization of post-translational modifications.
使用叔胺或季胺标记试剂对胰蛋白酶肽的羧基进行衍生,以产生电荷更高的肽离子,从而通过电子转移解离(ETD)有效地进行碎裂。所有肽的羧基--天冬氨酸和谷氨酸侧链以及 C 端--都进行了衍生,平均反应效率为 99%。这种近乎完全的标记避免了因部分标记产物而使复杂的多肽混合物变得更加复杂,而且还可以在数据库搜索时使用静态修饰。在测试的四种试剂中,烷基叔胺是最佳的标记试剂。衍生肽的电荷状态要高得多:经修饰的牛血清白蛋白(BSA)胰蛋白酶消化物产生的前体离子中约有 90% 的 z > 2,而未经修饰的样品则不到 40%。修饰肽离子电荷密度的增加产生了高效的 ETD 片段,从而增加了许多肽的鉴定率和更高的序列覆盖率(例如,修饰肽离子的鉴定率为 70%,而未修饰 BSA 的鉴定率仅为 43%)。从酵母细胞中分离出来的核糖体蛋白质的胰蛋白酶消化物证明了这种标记策略的实用性。对该样本进行肽衍生处理后,鉴定出的蛋白质数量增加了,这些蛋白质的序列覆盖率提高了 50%以上,肽谱匹配的数量也增加了一倍。这种羧基衍生化策略大大提高了从胰蛋白酶消化物的 ETD-MS/MS 中获得的蛋白质组覆盖率,我们预计它还将提高翻译后修饰的鉴定和定位。