A structural analysis of heparin-like glycosaminoglycans using MALDI-TOF mass spectrometry

Abstract

Mass spectrometry (MS) techniques have spear-headed the field of proteomics. Recently, MS has been used to structurally analyse carbohydrates. The heparin/heparan sulfate-like glycosaminoglycans (HLGAGs) present a special set of difficulties for structural analysis because they are highly sulfated and heterogeneous. We have used a matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-MS) technique in which heparin fragments are non-covalently bound to basic peptides of a known mass, so as to limit in-source desulfation and hence afford an accurate mass. We examined a range of different sized fragments with varying degrees of sulfation. The potential of combining the MALDI-MS technique with enzymatic digestion to obtain saccharide sequence information on heparin fragments was explored. A disaccharide analysis greatly assists in determining a sequence from MALDI-MS data. Enzymatic digestion followed by MALDI-MS allows structural data on heparin fragments too large for direct MALDI-MS to be obtained. We demonstrate that synthetic sulfated oligosaccharides can also be analysed by MALDI-MS. There are advantages and limitations with this methodology, but until superior MS techniques become readily accessible to biomedical scientists the MALDI-MS method provides a means to structurally analyse HLGAG fragments that have therapeutic potential because of their ability to bind to and functionally regulate a host of clinically important proteins.