MALDI-In Source Decay Applied to Mass Spectrometry Imaging: A New Tool for Protein Identification

Matrix-assisted laser desorption/ionization (MALDI) is now a mature method allowing the identification and, more challenging, the quantification of biopolymers (proteins, nucleic acids, glycans, etc). 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 MS3 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 (PTMs) studies, and finally review MALDI-ISD tissue imaging applications.

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“…These results open the way towards de novo sequencing, directly from tissue slices. The method was applied for biomarkers discovery [95,96].…”

Section: Maldi-isd On Tissue Slicesmentioning

confidence: 99%

MALDI In-Source Decay, from Sequencing to Imaging

Debois

Smargiasso

Demeure

et al. 2012

Topics in Current Chemistry

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“…These matrixes exhibit a propensity to readily provide H • during the MALDI process and this possibility can induce extensive in-source fragmentations. Thus, matrix selection is an important parameter for ISD experiments, and the tendency of a given molecule toward fragmentation is clearly matrixdependent [32].…”

Section: Maldi In-source Decay (Isd) Of Pomc12 Mechanism Of Decomposmentioning

confidence: 99%

“…To further investigate the POM fragmentation processes, MS/MS through LIFT experiments [39], which invoke similar processes as post-source decay (PSD) [32], were performed for POMc12 adduct ions, but no fragmentations were observed. The molecular adduct ion, comprised of POMc12 and cations, thus seems to either fragment suddenly (ISD), even with 0 ns of extraction delay time value, or remain intact over the metastable time scale.…”

Section: Maldi In-source Decay (Isd) Of Pomc12 Mechanism Of Decomposmentioning

confidence: 99%

Negative Ion MALDI Mass Spectrometry of Polyoxometalates (POMs): Mechanism of Singly Charged Anion Formation and Chemical Properties Evaluation

Boulicault

Alvès

Cole

2016

J. Am. Soc. Mass Spectrom.

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Abstract. MALDI-MS has been developed for the negative ion mode analysis of polyoxometalates (POMs). Matrix optimization was performed using a variety of matrix compounds. A first group of matrixes offers MALDI mass spectra containing abundant intact singly charged anionic adduct ions, as well as abundant in-source fragmentations at elevated laser powers. A relative ranking of the ability to induce POM fragmentation is found to be: DAN > CHCA > CNA > DIT> HABA > DCTB > IAA. Matrixes of a second group provide poorer quality MALDI mass spectra without observable fragments. Sample preparation, including the testing of salt additives, was performed to optimize signals for a model POM, POMc12, the core structure of which bears four negative charges. The matrix 9-cyanoanthracene (CNA) provided the best signals corresponding to singly charged intact POMc12 anions. Decompositions of these intact anionic species were examined in detail, and it was concluded that hydrogen radical-induced mechanisms were not prevalent, but rather that the observed prompt fragments originate from transferred energy derived from initial electronic excitation of the CNA matrix. Moreover, in obtained MALDI mass spectra, clear evidence of electron transfer to analyte POM species was found: a manifestation of the POMs ability to readily capture electrons. The affinity of polyanionic POMc12 toward a variety of cations was evaluated and the following affinity ranking was established: Fe 3+ > Al 3+ > Li + > Ga 3+ > Co 2+ > Cr 3+ > Cu 2+ > [Mn 2+ , Mg 2+ ] > [Na + , K + ]. Thus, from the available cationic species, specific adducts are preferentially formed, and evidence is given that these higher affinity POM complexes are formed in the gas phase during the early stages of plume expansion.

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“…However, the top-down method without ion selection can be used with MALDI to rapidly generate fragmentation using ISD [39][40][41][42][43][44][45][46]. ISD has been demonstrated previously [33] for tissue sections. However, because ISD is not used with ion selection, the resulting mass spectra are extremely difficult to interpret.…”

Section: In-source Decay Approachmentioning

confidence: 99%

“…This concept of data mining was also applied to data sets generated for identification. In fact, protein identification using direct imaging strategies has been shown to be possible either by enzymatic digestion using tissue bottom-up approaches [10,31,32] or by in-source decay (ISD) with top-down approaches [33]. Such strategies also produce large quantity of data, and markers of interest may be masked within the forest of non-relevant data.…”

Section: Introductionmentioning

confidence: 99%

Multivariate analyses for biomarkers hunting and validation through on-tissue bottom-up or in-source decay in MALDI-MSI: application to prostate cancer

Bonnel

Longuespée

Franck³

et al. 2011

Anal Bioanal Chem

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The large amount of data generated using matrixassisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) poses a challenge for data analysis. In fact, generally about 1.10 8 -1.10 9 values (m/z, I) are stored after a single MALDI-MSI experiment. This imposes processing techniques using dedicated informatics tools to be used since manual data interpretation is excluded. This work proposes and summarizes an approach that utilizes a multivariable analysis of MSI data. The multivariate analysis, such as principal component analysis-symbolic discriminant analysis, can remove and highlight specific m/z from the spectra in a specific region of interest. This approach facilitates data processing and provides better reproducibility, and thus, broadband acquisition for MALDI-MSI should be considered an effective tool to highlight biomarkers of interest. Additionally, we demonstrate the importance of the hierarchical classification of biomarkers by analyzing studies of clusters obtained either from digested or undigested tissues and using bottom-up and in-source decay strategies for in-tissue protein identification. This provides the possibility for the rapid identification of specific markers from different histological samples and their direct localization in tissues. We present an example from a prostate cancer study using formalinfixed paraffin-embedded tissue.

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MALDI-In Source Decay Applied to Mass Spectrometry Imaging: A New Tool for Protein Identification

Cited by 97 publications

References 35 publications

MALDI In-Source Decay, from Sequencing to Imaging

MALDI In-Source Decay, from Sequencing to Imaging

Negative Ion MALDI Mass Spectrometry of Polyoxometalates (POMs): Mechanism of Singly Charged Anion Formation and Chemical Properties Evaluation

Multivariate analyses for biomarkers hunting and validation through on-tissue bottom-up or in-source decay in MALDI-MSI: application to prostate cancer

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