GLYCOPROTEIN ANALYSIS BY DELAYED EXTRACTION AND POST-SOURCE DECAY MALDI-TOF-MS

Matrix-assisted laser desorption-ionization (MALDI)-MS analysis of gly coprotein samples is usually affected by metastable fragmentation, par ticularly 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 dis ialylated component gives the most abundant MALDI signal with a dramat ically improved resolution and mass accuracy over the non-DE linear TO F analysis. This increased resolution is advantageous for the 30 kDa S f9-derived IL-4 receptor, where it is possible to differentiate the in dividual glycans, but not for higher mass and more heterogeneous glyco proteins. It is also shown that MALDI analysis of proteins with labile functional groups is more superior and reliable with linear DE-TOF sy stems rather than reflectron TOF analyzers. Further structural informa tion on the sequence and disulfide mapping, as well as glycopeptide id entification can be obtained by post-source decay (PSD) analysis of pe ptide and glycopeptide isolated fractions. The PSD formation of a char acteristic tripler of ions separated by 33 Da in mass can be used to i dentify disulfide-paired peptides, even from complex digest mixtures o f proteins. (C) 1997 Elsevier Science B.V.