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Replacing H+ by Na+ or K+ in phosphopeptide anions and cations prevents electron capture dissociation.

ABSTRACT: By successively replacing H+ by Na+ or K+ in phosphopeptide anions and cations, we show that the efficiency of fragmentation into c and z? or c? and z fragments from N-C? backbone bond cleavage by negative ion electron capture dissociation (niECD) and electron capture dissociation (ECD) substantially decreases with increasing number of alkali ions attached. In proton-deficient phosphopeptide ions with a net charge of 2-, we observed an exponential decrease in electron capture efficiency with increasing number of Na+ or K+ ions attached, suggesting that electrons are preferentially captured at protonated sites. In proton-abundant phosphopeptide ions with a net charge of 3+, the electron capture efficiency was not affected by replacing up to four H+ ions with Na+ or K+ ions, but the yield of c, z? and c?, z fragments from N-C? backbone bond cleavage generally decreased next to Na+ or K+ binding sites. We interpret the site-specific decrease in fragmentation efficiency as Na+ or K+ binding to backbone amide oxygen in competition with interactions of protonated sites that would otherwise lead to backbone cleavage into c, z? or c?, z fragments. Our findings seriously challenge the hypothesis that the positive charge responsible for ECD into c, z? or c?, z fragments can generally be a sodium or other metal ion instead of a proton.

SUBMITTER: Schneeberger EM

PROVIDER: S-EPMC6237128 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Replacing H+ by Na+ or K+ in phosphopeptide anions and cations prevents electron capture dissociation.

Schneeberger Eva-Maria EM Breuker Kathrin K

Chemical science 20180726 37

By successively replacing H+ by Na+ or K+ in phosphopeptide anions and cations, we show that the efficiency of fragmentation into c and z˙ or c˙ and z fragments from N-Cα backbone bond cleavage by negative ion electron capture dissociation (niECD) and electron capture dissociation (ECD) substantially decreases with increasing number of alkali ions attached. In proton-deficient phosphopeptide ions with a net charge of 2-, we observed an ...[more]

PMID: 30542537

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Project description:Fast photochemical oxidation of proteins (FPOP) footprinting is a structural mass spectrometry method that maps proteins by fast and irreversible chemical reactions. The position of oxidative modification reflects solvent accessibility and site reactivity and thus provides information about protein conformation, structural dynamics, and interactions. Bottom-up mass spectrometry is an established standard method to analyze FPOP samples. In the bottom-up approach, all forms of the protein are digested together by a protease of choice, which results in mixture of peptides from various subpopulations of proteins with varying degrees of photochemical oxidation. But, once the protein is already oxidized at least once, the spatial distribution of any consecutive oxidation no longer truly reflects initial protein solvent accessibility and residue reactivity, because the site preference of further oxidation may also be influenced by the changes caused by the prior oxidation. Thus, it would be interesting to obtain an assessment of the protein structure based on the FPOP data, by analyzing only singly oxidized protein populations. This requires utilization of more specific top-down mass spectrometry approaches. The key element of any top-down experiment is selection of a suitable method of ion isolation, excitation and fragmentation. Here we employ and compare collision-induced dissociation (CID), electron-transfer dissociation (ETD), and electron-capture dissociation (ECD) combined with multi continuous accumulation of selected ions (CASI). Singly oxidized subpopulation of FPOP labeled ubiquitin was used to optimize the method. The usefulness was then demonstrated further by using it to visualize structural changes induced by cofactor removal from holo/apo myoglobin system. The top-down data were compared with the literature and with the bottom-up data set obtained on the same samples. The top-down results were found to be in a good agreement, which indicates that monitoring singly FPOP oxidized ion population by top-down is a functional workflow for oxidative protein footprinting.

Dataset Information

Replacing H+ by Na+ or K+ in phosphopeptide anions and cations prevents electron capture dissociation.

Publications

Replacing H<sup>+</sup> by Na<sup>+</sup> or K<sup>+</sup> in phosphopeptide anions and cations prevents electron capture dissociation.

Similar Datasets

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