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Charge site mass spectra: conformation-sensitive components of the electron capture dissociation spectrum of a protein.

ABSTRACT: A conventional electron capture dissociation (ECD) spectrum of a protein is uniquely characteristic of the first dimension of its linear structure. This sequence information is indicated by summing the primary c (m+) and z (m+•) products of cleavage at each of its molecular ion's inter-residue bonds. For example, the ECD spectra of ubiquitin (M?+?nH)(n+) ions, n?=?7-13, provide sequence characterization of 72 of its 75 cleavage sites from 1843 ions in seven c ((1-7)+) and eight z ((1-8)+•) spectra and their respective complements. Now we find that each of these c/z spectra is itself composed of "charge site (CS)" spectra, the c (m+) or z (m+•) products of electron capture at a specific protonated basic residue. This charge site has been H-bonded to multiple other residues, producing multiple precursor ion forms; ECD at these residues yields the multiple products of that CS spectrum. Closely similar CS spectra are often formed from a range of charge states of ubiquitin and KIX ions; this indicates a common secondary conformation, but not the conventional ?-helicity postulated previously. CS spectra should provide new capabilities for comparing regional conformations of gaseous protein ions and delineating ECD fragmentation pathways.

SUBMITTER: Skinner OS

PROVIDER: S-EPMC3730536 | biostudies-literature | 2013 Jun

REPOSITORIES: biostudies-literature

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Charge site mass spectra: conformation-sensitive components of the electron capture dissociation spectrum of a protein.

Skinner Owen S OS Breuker Kathrin K McLafferty Fred W FW

Journal of the American Society for Mass Spectrometry 20130403 6

A conventional electron capture dissociation (ECD) spectrum of a protein is uniquely characteristic of the first dimension of its linear structure. This sequence information is indicated by summing the primary c (m+) and z (m+•) products of cleavage at each of its molecular ion's inter-residue bonds. For example, the ECD spectra of ubiquitin (M + nH)(n+) ions, n = 7-13, provide sequence characterization of 72 of its 75 cleavage sites from 1843 ions in seven c ((1-7)+) and eight z ((1-8)+•) spect ...[more]

PMID: 23549668

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Project description:Herein, we focus on native mass spectrometry (nMS) combined with a fast, tunable gas-phase charge reduction, electron capture charge reduction (ECCR), and illustrate its utility in the characterization of protein complex topology and glycoprotein heterogeneity. ECCR is illustrated to effectively spread the charge states of tetradecameric GroEL, illustrating Orbitrap m/z measurement out to greater than 100,000 m/z. For both the pentameric C-reactive protein and tetradecameric GroEL, our novel device combining ECCR with surface induced dissociation (SID) lowers the charge states and produces more topologically informative fragmentation. While more native-like fragmentation has previously been illustrated for complexes charge reduced by proton abstraction in solution, this is the first illustration that ECCR can lead to more native-like SID fragmentation of protein complexes. Application to protein glycosylation, one of the most common and diverse protein posttranslational modifications, is also illustrated because glycosylation is important for structural and functional properties and plays essential roles in many key biological processes. The immense heterogeneity resulting from variability in glycosylation sites and glycan composition and structure poses significant analytical challenges that hinder a mechanistic understanding of the biological role of glycosylation. Data for stabilized heavily glycosylated SARS-CoV-2 spike protein trimer and thyroglobulin dimer illustrate that ECCR enables significantly improved resolution of glycan heterogeneity. Without ECCR, the charge states of a glycoprotein complex are not resolved and average mass determination is available only through the use of charge detection mass spectrometry or mass photometry. With ECCR after narrow m/z selection, multiple glycoform m/z values are apparent, providing quick global, glycoform profiling and providing a future path for glycan localization on individual intact glycoforms (e.g., though top-down dissociation).

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Dataset Information

Charge site mass spectra: conformation-sensitive components of the electron capture dissociation spectrum of a protein.

Publications

Charge site mass spectra: conformation-sensitive components of the electron capture dissociation spectrum of a protein.

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