"Glyco-peakfinder"--de novo composition analysis of glycoconjugates.

Mass spectrometric techniques are the key technology for rapid and reliable glycan analysis. However, the lack of robust, dependable, and freely available software for the (semi-) automatic annotation of mass spectra is still a severe bottleneck that hampers their rapid interpretation. In this article the "Glyco-Peakfinder" web-service is described allowing de novo determination of glycan compositions from their mass signals. Starting from a basic set of mandatory masses of glycan components, the calculation can be performed without any knowledge concerning the biological background of the sample or the fragmentation technique used. "Glyco-Peakfinder" assigns all types of fragment ions including monosaccharide cross-ring cleavage products and multiply charged ions. It provides full user control to handle modified glycans (persubstituted molecules, reducing-end modifications, glycoconjugates) and ion types. The formula applied to calculate the fragment masses and an outline of the implemented algorithm are discussed. A systematic evaluation of the dependence of all factors influencing the computation time revealed strikingly different impact of the individual calculation steps. To provide access to known carbohydrate structures a "composition search" in the open access database GLYCOSCIENCES.de can be performed. The service is available at the URL: www.eurocarbdb.org/applications/ms-tools.