Quantitative fingerprinting of O-linked glycans released from proteins using isotopic coded labeling with deuterated...

Investigation of oligosaccharides attached to proteins as post-translational modification remains an important research field in the area of glycoproteomics as well as in biotechnology. The development of new tools for qualitative and quantitative analysis of glycans has gained high importance in recent years. This is particularly true with O-glycans for which quantitative data are still underrepresented in literature. This fact is probably due to the absence of an enzyme for general release of O-linked saccharides from glycoproteins and due to their low ionization yield in mass spectrometry (MS). In this paper, a method is established aimed at improved qualitative and quantitative analysis of mucin-type O-glycans. A chemical reaction combining release and derivatization of O-glycans in one step is combined here with mass spectrometric quantification. For the purpose of improved quantitative analysis, stable-isotope coded labeling by d0/d5 1-phenyl-3-methyl-5-pyrazolidone (PMP) was performed. The "heavy"-version of this label, penta-deutero (d5)-PMP, was synthesized for this purpose. Beneath improving the reproducibility of quantitation, PMP derivatization contributed to an enhancement of ionization yields in MS. By introducing an internal standard (e.g. GlcNAc3) the reproducibility for quantification can be improved. For higher abundant O-glycans a mean coefficient of variation (CV) less than 6% could be attained, for very low abundant CV values between 15 and 20%. For the determination of O-glycan profiles in mixtures, a HPLC separation was combined with a high resolution Qq-oaTOF instrument. RP-type stationary phases were successful in separating glycan species including some of isomeric ones. This separation step was particularly useful for removing of salts avoiding so the presence of various sodium clusters in the MS spectrum.