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See detailMALDI In-Source Decay, from sequencing to imaging
Debois, Delphine ULg; Smargiasso, Nicolas ULg; Demeure, Kevin ULg et al

in Topics in Current Chemistry (2013), 331

MALDI is now a mature method allowing the identification and, more challenging, the quantification of biopolymers (proteins, nucleic acids, glycans…). MALDI spectra show mostly intact singly charged ions ... [more ▼]

MALDI is now a mature method allowing the identification and, more challenging, the quantification of biopolymers (proteins, nucleic acids, glycans…). MALDI spectra show mostly intact singly charged ions. To obtain fragments, the activation of singly charged precursors is necessary, but not efficient above 3.5 kDa thus making MALDI MS/MS difficult for large species. In-source decay (ISD) is a prompt fragmentation reaction that can be induced thermally or by radicals. As fragments are formed in the source, precursor ions cannot be selected; however, the technique is not limited by the mass of the analyzed compounds and pseudo MS/MS can be performed on intense fragments. The discovery of new matrices that enhance the ISD yield, combined with the high sensitivity of MALDI mass spectrometers, and software development, opens new perspectives. We first review the mechanisms involved in the ISD processes, then discuss ISD applications like top-down sequencing and post-translational modifications studies, and finally review MALDI-ISD tissue imaging applications. [less ▲]

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See detailNew Advances in the Understanding of the In-Source Decay Fragmentation of Peptides in MALDI-TOF-MS.
Demeure, Kevin ULg; Gabelica, Valérie ULg; De Pauw, Edwin ULg

in Journal of the American Society for Mass Spectrometry (2010), 21(11), 1906-17

In-source decay (ISD) is a rapid fragmentation occurring in the matrix-assisted laser desorption/ionization (MALDI) source before the ion extraction. Despite the increasing interest for peptides de novo ... [more ▼]

In-source decay (ISD) is a rapid fragmentation occurring in the matrix-assisted laser desorption/ionization (MALDI) source before the ion extraction. Despite the increasing interest for peptides de novo sequencing by ISD, the influence of the matrix and of the peptide itself is not yet fully understood. Here we compare matrices with high ISD efficiencies to gain deeper insight in the ISD fragmentation process(es). The major ISD fragments are the c- and z-ions, but other types of fragments are also observed, and their origin is studied here. Two main pathways lead to fragmentation in the source: a radical-induced pathway that leads to c-, z-, w-, and d-ions, and a thermally activated pathway that leads to y-, b-, and a-ions. A detailed analysis of the ISD spectra of selected peptides revealed that (1) the extents of the two in-source pathways are differently favored depending on the matrix used, that (2) the presence of a positive/negative charge on the radical-induced fragments is necessary for their observation in positive/negative mode, respectively, and that (3), for a same peptide, the patterns of the different types of fragments differ according to the matrix used. [less ▲]

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See detailMALDI-Top-Down of Proteins: Overview and Applications
Quinton, Loïc ULg; Demeure, Kevin ULg; Resemann, Anja et al

Conference (2009, June)

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See detailTop-Down Proteomics using Matrix-Enhanced ISD
Demeure, Kevin ULg; Quinton, Loïc ULg; Gabelica, Valérie ULg et al

Poster (2007, October 11)

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See detailTop-Down Proteomics using Matrix-Enhanced ISD
Demeure, Kevin ULg; Quinton, Loïc ULg; Gabelica, Valérie ULg et al

Conference (2007, June 05)

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See detailRational selection of the optimum MALDI matrix for top-down proteomics by in-source decay
Demeure, Kevin ULg; Quinton, Loïc ULg; Gabelica, Valérie ULg et al

in Analytical Chemistry (2007), 79(22), 8678-8685

in-source decay (ISD) in MALDI leads to c- and z-fragment ion series enhanced by hydrogen radical donors and is a useful method for sequencing purified peptides and proteins. Until now, most efforts to ... [more ▼]

in-source decay (ISD) in MALDI leads to c- and z-fragment ion series enhanced by hydrogen radical donors and is a useful method for sequencing purified peptides and proteins. Until now, most efforts to improve methods using ISD concerned instrumental optimization. The most widely used ISD matrix is 2,5-dihydroxybenzoic acid (DHB). We present here a rational way to select MALDI matrixes likely to enhance ISD for top-down proteomic approaches. Starting from Takayama's model (Takayama, M. J. Am. Soc. Mass Spectrom. 2001, 12, 1044-9), according to which formation of ISD fragments (c and z) would be due to a transfer of hydrogen radical from the matrix to the analyte, we evaluated the hydrogen-donating capacities of matrixes, and thus their ISD abilities, with spirooxazines (hydrogen scavengers). The determined hydrogen-donating abilities of the matrixes are ranked as follows: picolinic acid (PA) > 1,5-diaminonaphtalene (1,5-DAN) > DHB > sinapinic acid > alpha-cyano-4-hydroxycinnamic acid. The ISD enhancement obtained by using 1,5-DAN compared to DHB was confirmed with peptides and proteins. On that basis, a matrix-enhanced ISD approach was successfully applied to sequence peptides and proteins up to similar to 8 kDa. Although PA alone is not suitable for peptide and protein ionization, ISD signals could be further enhanced when PA was used as an additive to 1,5-DAN. The optimized matrix preparation was successfully applied to identify larger proteins by large ISD tag researches in protein databases (BLASTp). Coupled with an adequate separation method, ISD is a promising tool to include in a top-down proteomic strategy. [less ▲]

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