Electron Capture Dissociation
Electron Capture Dissociation (ECD) was first applied to biomolecules by Zubarev et al. (1) from the McLafferty Group. ECD has the remarkable and useful ability to produce odd-electron, free-radical driven fragmentation of the same type as are generated by EI mass spectrometry (2). This fragmentation method generates different and often complementary fragmentation patterns when compared with Collisionally Activated Dissociation (CAD), Infrared Multiphoton Dissociation (IRMPD), or other slow, even-electron fragmentation methods.
For proteins, ECD cleaves between the backbone amide and the alpha carbon to form C and Z* fragments (where “*” refers to the radical “dot” symbol which unfortunately is unavailable on this keyboard). Moreover, the cleavage sites show very little selectivity for particular amino acids with the two exceptions of disulphide bonds (having high radical affinity) and proline (which is cyclic around the amide - alpha carbon and therefore requires breaking 2 bonds).
Additionally, for proteins, labile post-translational modifications such as phosphorylation sites, o-glycosylation sites, n-glycosylation sites, and others remain attached to the backbone during ECD MS/MS experiments allowing determination of the site and identity of post-translational modifications.
We are currently investigating the use of ECD for the analysis of novel post-translational modifications to proteins, and particularly for the analysis of glycosylation sites on glycopeptides. We currently have one paper submitted on this and will discuss it further when it is published.
1. Zubarev, R. A.; Kelleher, N. L.; McLafferty, F. W. Electron Capture Dissociation of Multiply Charged Protein Cations - a Nonergodic Process J. Am. Chem. Soc. 1998, 120, 3265-3266.
2. McLafferty, F. W.; Turecek, F. Interpretation of Mass Spectra; Fourth ed.; University Science Books: Mill Valley, CA, 1993.