| Ola Saad
Department Of Chemistry
Genome Center
University of California
Davis, CA 95616
(530) 754-4038
osaad@ucdavis.edu | Position: | Graduate Student | | Education: | B.S. Chemistry (Biochemistry emphasis), Saint Mary's College of California, 2000 | | Research Topic: | Structural characterization of glycosaminoglycans using mass spectrometry | | Research Summary: | The cell surface landscape is copiously covered with carbohydrates modifying proteins and lipids in the plasma membrane. These oligosaccharides mediate a variety of functions in the body through modulation of interactions between cells and with extracellular matrix components. However, the role of oligosaccharide structure as regards function has been minimally studied due to the complexity of these biomolecules and the limitations of the analytical methods used to study them. One of our objectives, in the Leary lab, is to develop methods for carbohydrate structural elucidation using mass spectrometry. My research focuses on the study of sulfated carbohydrates, specifically glycosaminoglycan analysis and determination of sulfate position.
Heparin and heparan sulfate (HS) glycosaminoglycans (GAGs), which are involved in the regulation of many (patho)physiological processes, consist of a variably sulfated repeating disaccharide unit. In fact, the high degree of sulfation of heparin gives it the highest charge density of any known biological macromolecule, further complicating its analysis. Methods I have developed use a combination of electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MSn) for the compositional analysis of the disaccharide constituents of heparin/HS, as well as towards sequencing larger heparin/HS oligosaccharides. My work has included fundamental isotopic labeling studies to study dissociation mechanisms of these saccharides upon collision induced dissociation, as well as the development of quantification methods for determining heparin disaccharide composition profiles after enzymatic digestion.
Furthermore, for the sequencing of low molecular weight heparin/HS oligosaccharides, my approach utilizes the combination of our novel ESI-MSn disaccharide composition analysis using method and direct MSn analysis of the saccharide. From MSn analysis, isolation and activation of the molecular ion with a high charge state yields a spectrum consisting of product ions generated mainly through glycosidic and cross-ring cleavages, with minimal loss of sulfate. With the help of HOST (Heparin Oligosaccharide Sequencing Tool), a new EXCEL-based software application I am developing, the data generated from both MS experiments can be integrated and analyzed to provide sequence information in much the same way that peptide mapping is currently done from MS/MS data. This methodology is currently being applied to various heparin oligosaccharides isolated from partial enzymatic digests of heparin/HS, as well as to heparin fragments that are found to be ligands that bind to and influence the function of different protein targets.
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