Sanjeev Kumar, , , Marimuthu Vijayasarathy, , , Venkatesha M. Achanna, , and , Padmanabhan Balaram*,
{"title":"Side Chain Driven Mass Spectral Fragmentation of Lys Containing Peptides: Cα-CO Bond Cleavage in Xxx-Lys-Xxx Sequences","authors":"Sanjeev Kumar, , , Marimuthu Vijayasarathy, , , Venkatesha M. Achanna, , and , Padmanabhan Balaram*, ","doi":"10.1021/jasms.5c00154","DOIUrl":null,"url":null,"abstract":"<p >Mass spectral fragmentation of the tripeptide amide Ala-Lys-Ala-amide (AKA*) yields a product ion at <i>m</i>/<i>z</i> 228.1, which corresponds to a neutral loss of 43 Da from the <i>b</i><sub>3</sub> ion (<i>m</i>/<i>z</i> 271.1). Similar losses of 43 Da are observed from <i>b</i><sub>n</sub> ions in the hexapeptide AKAAKA* and tetrapeptide AKAA*. The role of the Lys2 residue, in mediating the neutral loss, is supported by the absence of the corresponding product ion in the MS<sup>2</sup> spectrum of AVA* and attenuation of the intensity in analogs containing ornithine/diaminobutyric acid residues at position 2. The role of the N-terminus amino group is suggested by the absence of this neutral loss when the residue Ala1 amino group is acetylated or dimethylated. In XKA* sequences, where X = Gly, Ala, Leu, Aib and Pro, the observed neutral losses from <i>b</i><sub>3</sub> are 29, 43, 85, 57, and 69 Da, respectively, indicative of C<sup>α</sup>-CO bond cleavage releasing the R-CH = NH fragment. Isotope labeling and comparison with mass spectral fragments generated from synthetic N<sup>α</sup>-formyl Lys-Ala-amide (fKA*) establish the identity of the ion at <i>m</i>/<i>z</i> 228 in the MS<sup>2</sup> spectrum of AKA* as the <i>b</i> ion [fKA]. A charge remote fragmentation pathway, involving proton abstraction from the terminal amino group, by the Lys2 ε amino group, followed by C<sup>α</sup>-CO bond cleavage, is proposed as a plausible mechanism for the observed noncanonical cleavage process.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":"36 10","pages":"2134–2141"},"PeriodicalIF":2.7000,"publicationDate":"2025-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of the American Society for Mass Spectrometry","FirstCategoryId":"92","ListUrlMain":"https://pubs.acs.org/doi/10.1021/jasms.5c00154","RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"BIOCHEMICAL RESEARCH METHODS","Score":null,"Total":0}
引用次数: 0
Abstract
Mass spectral fragmentation of the tripeptide amide Ala-Lys-Ala-amide (AKA*) yields a product ion at m/z 228.1, which corresponds to a neutral loss of 43 Da from the b3 ion (m/z 271.1). Similar losses of 43 Da are observed from bn ions in the hexapeptide AKAAKA* and tetrapeptide AKAA*. The role of the Lys2 residue, in mediating the neutral loss, is supported by the absence of the corresponding product ion in the MS2 spectrum of AVA* and attenuation of the intensity in analogs containing ornithine/diaminobutyric acid residues at position 2. The role of the N-terminus amino group is suggested by the absence of this neutral loss when the residue Ala1 amino group is acetylated or dimethylated. In XKA* sequences, where X = Gly, Ala, Leu, Aib and Pro, the observed neutral losses from b3 are 29, 43, 85, 57, and 69 Da, respectively, indicative of Cα-CO bond cleavage releasing the R-CH = NH fragment. Isotope labeling and comparison with mass spectral fragments generated from synthetic Nα-formyl Lys-Ala-amide (fKA*) establish the identity of the ion at m/z 228 in the MS2 spectrum of AKA* as the b ion [fKA]. A charge remote fragmentation pathway, involving proton abstraction from the terminal amino group, by the Lys2 ε amino group, followed by Cα-CO bond cleavage, is proposed as a plausible mechanism for the observed noncanonical cleavage process.
期刊介绍:
The Journal of the American Society for Mass Spectrometry presents research papers covering all aspects of mass spectrometry, incorporating coverage of fields of scientific inquiry in which mass spectrometry can play a role.
Comprehensive in scope, the journal publishes papers on both fundamentals and applications of mass spectrometry. Fundamental subjects include instrumentation principles, design, and demonstration, structures and chemical properties of gas-phase ions, studies of thermodynamic properties, ion spectroscopy, chemical kinetics, mechanisms of ionization, theories of ion fragmentation, cluster ions, and potential energy surfaces. In addition to full papers, the journal offers Communications, Application Notes, and Accounts and Perspectives