Simultaneous Release and Labeling of <i>O</i>- and <i>N</i>‑Glycans Allowing for Rapid Glycomic Analysis by Online LC-UV-ESI-MS/MS

Most glycoproteins and biological protein samples undergo both <i>O</i>- and <i>N</i>-glycosylation, making characterization of their structures very complicated and time-consuming. Nevertheless, to fully understand the biological functions of glycosylation, both the glycosylation forms need to be analyzed. Herein we report a versatile, convenient one-pot method in which <i>O</i>- and <i>N</i>-glycans are simultaneously released from glycoproteins and chromogenically labeled in situ and thus available for further characterization. In this procedure, glycoproteins are incubated with 1-phenyl-3-methyl-5-pyrazolone (PMP) in aqueous ammonium hydroxide, making <i>O</i>-glycans released from protein backbones by β-elimination and <i>N</i>-glycans liberated by alkaline hydrolysis. The released glycans are promptly derivatized with PMP in situ by Knoevenagel condensation and Michael addition, with peeling degradation almost completely prevented. The recovered mixture of <i>O</i>- and <i>N</i>-glycans as bis-PMP derivatives features strong ultraviolet (UV) absorbing ability and hydrophobicity, allowing for high-resolution chromatographic separation and high-sensitivity spectrometric detection. Using this technique, <i>O</i>- and <i>N</i>-glycans were simultaneously prepared from some model glycoproteins and complex biological samples, without significant peeling, desialylation, deacetylation, desulfation or other side-reactions, and then comprehensively analyzed by online HILIC-UV-ESI-MS/MS and RP-HPLC-UV-ESI-MS/MS, with which some novel <i>O</i>- and <i>N</i>-glycan structures were first found. This method provides a simple, versatile strategy for high-throughput glycomics analysis

Mass Spectrometric Analysis of <i>N</i>‑Glycoforms of Soybean Allergenic Glycoproteins Separated by SDS-PAGE

Glycosylation of many proteins has been revealed to be closely related with food allergies, and screening and structural analysis of related glycoproteins and glycoallergens are essential for studies in this field. Herein, we describe detailed <i>N</i>-glycoform analysis of all glycoprotein fractions of soybean protein isolate (SPI) separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to disclose structural features of the glycan moieties of more soybean glycoproteins. SPI was fractionated by SDS-PAGE, and the generated protein bands were recovered and subjected to in-gel <i>N</i>-glycan release and labeling using a one-pot method newly developed by our group, followed by detailed analysis by electrospray ionization mass spectrometry (ESI-MS) and online hydrophilic interaction liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HILIC-ESI-MS/MS). As a result, we found seven bands mainly containing oligomannose-type glycans; two mainly contain core α1,3-fucosylated glycans, and six have no glycans. This study is the first report that discovers core α1,3-fucosylated <i>N</i>-glycans in bands 1, 2, and 6 and discloses bands 3, 4, 5, and 7 as glycoproteins and their <i>N</i>-glycoforms. Therefore, it can expand our knowledge about soybean protein glycosylation and provide significant structural reference for research of soybean allergens