Glycoprotein analysis by delayed extraction and post-source decay MALDI-TOF-MS

Matrix-assisted laser desorption-ionization (MALDI)-MS analysis of glycoprotein samples is usually affected by metastable fragmentation, particularly in reflectron instruments. Use of delayed extraction (DE) is shown to minimize the observed metastable fragmentation. In the case of the CHO IL-4, which contains complex-type N-linked glycans, the disialylated component gives the most abundant MALDI signal with a dramatically improved resolution and mass accuracy over the non-DE linear TOF analysis. This increased resolution is advantageous for the 30 kDa Sf9-derived IL-4 receptor, where it is possible to differentiate the individual glycans, but not for higher mass and more heterogeneous glycoproteins. It is also shown that MALDI analysis of proteins with labile functional groups is more superior and reliable with linear DE-TOF systems rather than reflectron TOF analyzers. Further structural information on the sequence and disulfide mapping, as well as glycopeptide identification can be obtained by post-source decay (PSD) analysis of peptide and glycopeptide isolated fractions. The PSD formation of a characteristic tripler of ions separated by 33 Da in mass can be used to identify disulfide-paired peptides, even from complex digest mixtures of proteins. (C) 1997 Elsevier Science B.V.