Quantitative Matrix-assisted Laser Desorption/ionization Mass Spectrometry of Pyrene-derivatized Glycopeptides for Investigation of Mammalian Cell Glycomics

Glycan is one of the major information-rich biomolecules. Alterations in N-glycans can be associated with many diseases including cancer, and are often observed in the serum of affected patients. As an example, prostate-specific antigen (PSA) is a glycoprotein secreted by prostatic epithelial cells. The serum PSA assay is widely used for detection of prostate cancer (PCa). Detection of altered PSA glycan is regarded as a precise diagnosis. However, the limited amount of serum PSA available makes it difficult to determine detailed glycan structures, as the PSA level in serum is very low. Mass spectrometry (MS) is a powerful tool for analyzing glycan structures. We have recently established a highly sensitive MS for both glycans and glycopeptides by pyrene derivatization. Matrix-assisted laser desorption/ionizationquadrupole ion trap-time of flight (MALDI-QIT-TOF) mass spectra of glycans derivatized with pyrene butanoic acid hydrazide (PBH) were compared with those of pyridylaminated (PA) glycans. Each derivatized glycan was prepared from the same amount of commercial PSA. PBH-labeled PSA glycans showed higher signal intensity with less fragmentation compared with PA-glycans, and gave spectra with high s/n ratio (in both positive- and negative-ion modes). For derivatization of the glycopeptides, pyrenyl diazomethane (PDAM) was used. The glycopeptide signals were greatly enhanced by this derivatization. PDAM-glycopeptides prepared from about 10 ng of PSA could be determined. In this study, we demonstrated that MS analysis using pyrene derivatization provides higher sensitivity and stability for both glycans and glycopeptides, compared with HPLC and lectin affinity chromatography; furthermore comparable results were obtained to those seen with the other methods. We therefore conclude that our method is useful for investigation of mammalian cell glycomics.