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Top-down analyses use high-resolution mass spectrometry and aim to identify whole and intact biomolecules through their fine structural analysis. The direct analysis of intact biomolecules applies both in proteomics for the identification of peptido- and proteoforms but also in lipidomics for lipids.
PIXANIM has developed Top-down approaches in order to identify whole and intact biomolecules observed by MALDI-TOF mass spectrometry, from direct analysis of biological fluids, whole cells or tissue sections (by profiling or molecular imaging).
Since 2014, PIXANIM offers in particular the analysis of peptidoforms and proteoforms (< 25 kDa) with routine operational methodologies combining preparative liquid chromatography (fractionation/enrichment by gel filtration or reverse phase) and analyses by µLC-MS/MS of each fraction.

Compared to more classical strategies involving the analysis of peptides after proteolytic digestion (bottom-up approaches), the analysis of proteoforms and pepdiforms by a top-down approach remains poorly developed in France and elsewhere; partly because it requires very high-resolution mass spectrometry and dedicated bioinformatics tools.
The advantage of the Top-down approach in proteomics is that it can precisely measure the mass of a protein and then fragment it in order to obtain sequence labels enabling it to be identified and to characterise, in the same analysis, all the post-translational modifications carried by the latter.
These peptido-proteoforms are the major players in cells, tissues or organs that enter into the molecular mechanisms of physiological or pathological functioning. It is therefore important to have a better knowledge of endogenous biomolecules on both a structural and functional level, to follow their distribution in a detailed and dynamic way with their topography within the organs. Peptido-proteoforms observed in situ in biological fluids, cells and tissues are important targets in the search for new biomarkers.

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