A mass spectrometry database for identification of saponins in plants

Abstract

Saponins constitute an important class of secondary metabolites of the plant kingdom. Here, we present a mass spectrometry-based database for rapid and easy identification of saponins henceforth referred to as saponin mass spectrometry database (SMSD). With a total of 4196 saponins, 214 of which were obtained from commercial sources. Through liquid chromatography-tandem high-resolution/mass spectrometry (HR/MS) analysis under negative ion mode, the fragmentation behavior for all parent fragment ions almost conformed to successive losses of sugar moieties, α-dissociation and McLafferty rearrangement of aglycones in high-energy collision induced dissociation. The saccharide moieties produced sugar fragment ions from m/z (monosaccharide) to m/z (polysaccharides). The parent and sugar fragment ions of other saponins were predicted using the above mentioned fragmentation pattern. The SMSD is freely accessible at http://47.92.73.208:8082/ or http://cpu-smsd.com (preferrably using google). It provides three search modes (“CLASSIFY”, “SEARCH” and “METABOLITE”). Under the “CLASSIFY” function, saponins are classified with high predictive accuracies from all metabolites by establishment of logistic regression model through their mass data from HR/MS input as a csv file, where the first column is ID and the second column is mass. For the “SEARCH” function, saponins are searched against parent ions with certain mass tolerance in “MS Ion Search”. Then, daughter ions with certain mass tolerance are input into “MS/MS Ion Search”. The optimal candidates were screened out according to the match count and match rate values in comparison with fragment data in database. Additionally, another logistic regression model completely differentiated between parent and sugar fragment ions. This function designed in front web is conducive to search and recheck. With the “METABOLITE” function, saponins are searched using their common names, where both full and partial name searches are supported. With these modes, saponins of diverse chemical composition can be explored, grouped and identified with a high degree of predictive accuracy. This specialized database would aid in the identification of saponins in complex matrices particular in the study of traditional Chinese medicines or plant metabolomics.