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LASER-IMS Report Summary

Project ID: 320659
Funded under: FP7-IDEAS-ERC
Country: France

Final Report Summary - LASER-IMS (Coupling laser spectroscopy to mass spectrometry and ion mobility: from fundamentals to analytical sciences)

Mass spectrometry allows the analysis of biomolecular ions in a variety of different forms; for example as a function of charge state, bound to their targets or in multimers following aggregation. Ion mobility-mass spectrometry is a revolutionary technique regarding the separation of complex mixtures and structural isomers and can now play an important role in the study of the structure of protein and their complexes. In parallel, optical spectroscopy is also emerging as a key element in the gas phase methods available for investigating biomolecular ions. In this project, we combined spectroscopic approaches with high resolution mass spectrometry and ion mobility to widen and deepen the scope of mass spectrometry in its various fields of applications including structural biology, protein identification and quantification.

Concerning instrument and methodology, a new experimental setup that allows to perform tandem ion mobility spectrometry (IMS) measurements with the possibility of photo and collision excitation of the ions was built. In parallel, we developed Förster resonance energy transfer (FRET) in the gas phase, with a new approach called Action-FRET, for which FRET efficiency is measured through specific photofragmentation rather than fluorescence. Improvement of the fragmentation specificity to streamline data processing of bottom-up proteomic experiments in the discovery phase and in targeted quantification was reached through different photo-dissociation schemes including targeting of labeled peptides. Optical labeling was a key for specific targeting in proteomics and also for FRET, two routes were explored, the use of chromophores and of metal nanoclusters. The latters display specific chiral and non linear optical properties opening new possibilities for proteom and cell imaging. Experiments were supported by molecular dynamics simulations with development of adaptive biasing techniques, simulations of electronic and conformational changes.

A goal of this cross-disciplinary project was to study the structural reorganization of proteins occurring in relation to aggregation, radical formation and oxidation. We first focused on small oligomers of the amyloid beta protein, which have been implicated as the neurotoxic agent leading to Alzheimer's disease. Different alloforms were studied by a combination of action-FRET, ion-mobility spectrometry (IMS) and molecular dynamics simulations. Results will help to elucidate the origin of the large difference in aggregation behavior of the alloforms. Aβ1–42 peptide, tau and α-synuclein fibrils were also studied with a focus on the heterogeneity and polymorphism of the fibers.

The oxidative process of structural and enzymatic proteins, such as carbonylation and radical formation, modifies cellular metabolism and plays a fundamental role in the progression of human diseases and in the aging process. Oxidation was tackled through different approaches. Protein oxidation products were identified and quantified by mass spectrometry. The dynamics of oxidation, related charge transfers and of conformational changes were studied at different time-scales using both pump-probe experiments on trapped ions and tandem IMS. We also reported events involving multiple electron detachment.

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