Characterization of protein glycosylation using chip-based nanoelectrospray with precursor ion scanning quadrupole linear ion trap mass spectrometry.

Glycosylation is one of the most important posttranslational modifications affecting the functions of proteins and cell activities. Mass spectrometry (MS) has proven to be an effective tool for structural glycobiology and has helped gain an understanding of glycoprotein-mediated diseases. Although electro-spray ionization-tandem MS remains widely recognized as an effective means for oligosaccharide characterization, the hydrophilic nature of glycans has often caused the poor ionization efficiency requiring either derivatization or nanoelectrospray to improve detection sensitivity. In this report we describe the use of a chip-based infusion nanoelectrospray platform coupled with the hybrid triple quadrupole/linear ion trap for identification and characterization of glycosylation in complex mixtures. The high-mannose-type N-glycosylation in ribonuclease B was used to map the glycosylation site and obtain glycan structures. Using the chip-based nanoelectro-spray with precursor ion scanning linear ion trap MS, we were able to map the glycosylation site and obtain the glycan structures in ribonuclease B at 100 fmol/microL in a single analysis. In addition, a new, low-abundant glycoform with an additional hexose (Hex10GlcNAc2) attached to ribonuclease B was discovered. The results reported here demonstrate that the chip-based infusion nanoelectrospray ionization coupled to a quadrupole/linear ion trap platform is a valuable system, as it provides high sensitivity and stability for nanoelectrospray analysis, and allows extended acquisition time for completing precursor ion scanning and subsequent MS2 and MS3 information in a single analysis.