Deciphering the structure of oligosaccharides by a new tandem mass spectrometry method based on photo-activation in the VUV range
Résumé
Polysaccharides or degraded polysaccharides from plant or marine origin are widely used in pharmaceutical, cosmetics or food industries. The properties and end-uses of these molecules are tightly connected to their fine structure, although - for many of them - they remain unresolved. Deciphering carbohydrates structures in complex mixtures obviously challenges the field of analytical chemistry. Mass spectrometry, with its remarkable sensitivity, rapidity and high information content, is a forefront method for that purpose, although classical tandem mass spectrometry based on collision-activated dissociation (CAD) fails in many cases to achieve definitive structural assignments of carbohydrates. In this work, we explored an original instrumental setup using Vacuum Ultra-violet synchrotron radiation as activation process for tandem mass spectrometry1. A complex mixture of oligogalacturonans, released by the enzymatic degradation of highly methylated pectins and exhibiting many isomers differing by their methylation pattern was investigated. In striking contrast with CAD, photon activation in the VUV yielded outstanding information regarding these structures. In fact, the features that were observed on the fragmentation spectra are remarkable and bring straightforward and highly valuable structural information. This enabled to reach the most complete description by far of the products released from the enzymatic degradation of cell wall pectins, bringing insights both on the structure of these polymers as well as on the enzyme specificity.