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2030 Becker Drive MRB, Room 220D University of Kansas Lawrence, KS 66047-1620 Phone: (785) 864-3015 Fax: (785) 864-1916 Email: hdesaire@ku.edu |
Mass Spectrometry: Bioanalytical and Physical Organic Applications
Analytical Chemistry. Tandem mass spectrometry, HPLC-MS/MS, and CE-MS/MS. Organic reaction mechanisms and structural determination of glycoproteins.
Research in my group focuses on using mass spectrometry to study a variety of molecules, from large glycoproteins to simple bi-functional organic molecules. Structural information about the molecules is obtained using tandem mass spectrometry. In a tandem mass spectrometry experiment, the compound of interest is isolated inside the mass spectrometer; then, in a second step, it is fragmented. When the fragments are detected, a significant amount of structural information about the original compound is obtained. This technique can be used to characterize glycosylated proteins (see project 1) and small organic molecules, including pharmaceuticals (see project 2).
Project 1. Structural analysis of glycoproteins:
Glycoproteins are an important class of biological compounds. For example, gonadotropins, small glycoprotein hormones, regulate the activity of the pituitary. While these molecules are important biologically, they are very difficult to study, in part because of structural ambiguity of the carbohydrate on the protein. We take a novel approach to characterizing these compounds. First, the glycoprotein is subjected to enzymatic digestion, and glycopeptides are released. The resulting glycopeptides may be separated and are used in a variety of mass spectrometry studies. Different tandem mass spectrometric methods are explored to find an approach that provides the most structural information possible about the glycopeptides. By performing tandem mass spectrometry on the glycopeptides, we may be able to learn information about the glycoprotein structure that is not accessible using traditional approaches. Tandem mass spectrometry will be coupled with either HPLC (high-pressure liquid chromatography) or CE (capillary electrophoresis), so separation, detection, and analysis of the glycopeptides will be achieved in one step.
Project 2. Organic reaction mechanisms:
Another research focus in my group involves developing a "rule book" for the dissociation reactions observed in tandem mass spectrometry. Currently, there are no rules to explain how dissociations occur during tandem mass spectrometry (even though rules are available for higher-energy processes of electron impact or chemical ionization mass spectrometry.) We are developing a set of rules to explain when, where, and why dissociations occur, for various types of molecules. Using the fundamental principles of physical organic chemistry, hand-selected model compounds are used to study reaction mechanisms that occur during tandem mass spectrometry. Once rules that govern dissociation reactions are developed, tandem mass spectrometry will be more useful for researchers performing structural studies on small, organic molecules. One application of this work includes using our "rule book" to develop new approaches to studying pharmaceuticals. As a long-term goal, we will demonstrate that tandem mass spectra can be as effective as NMR (and much more efficient) to characterize certain types of metabolic byproducts of drugs.
Web-based tools developed and administered by the Desaire Group:
GlycoPep DB: (Used to assign glycan composition to MS data of glycopeptides)
URL: http://hexose.chem.ku.edu/sugar.php
GlycoPep ID: (Used to assign peptide composition to MS data of glycopeptides)
URL: http://hexose.chem.ku.edu/predictiontable.php
Go EP, Rebechi KR, Dalpathado DS, Bandu ML, Zhang Y, Desaire H.GlycoPep DB: A tool for glycopeptide analysis using a “smart search.” Anal Chem. In Press (2007).
Dalpathado DS, Irungu J, Go EP, Nortan K, Bousfield GR, Desaire H. Comparative glycomics of the glycoprotein Follicle-Stimulating Hormone (FSH): Glycopeptide analysis of isolates from two mammalian species. Biochemistry. 45, 8665-8673(2006).
Zhang Y, Jiang H, Go EP, Desaire H. Distinguishing phosphorylation and sulfation in carbohydrates and glycoproteins using ion-pairing and mass spectrometry. J. Am. Soc. Mass Spectrom. 17 (9): 1282-1288(2006).
Irungu J., Dalpathado DS, Go EP, Jiang H, Ha HV, Bousfield GR, Desaire H. A method for characterizing sulfated glycoproteins in a glycosylation site-specific fashion, using ion-pairing and tandem mass spectrometry. Anal Chem. 78, 1181-1190, (2006).
Bandu M, Wilson J, Vachet RW, Dalpathado DS, Desaire H. STEP Analysis (Statistical Test of Equivalent Pathways): A new mass spectrometric method for carbohydrates and peptides.” Anal Chem. 77,5886-5893 (2005).
Yi L, Bandu M, Desaire H. “Identifying lactone hydrolysis in pharmaceuticals: A tool for metabolite structural characterization.” Anal. Chem. 77, 6655-6663 (2005).
Desaire, H.; Leavell, M. D., Leary, J. A. "Solvent Effects in Tandem Mass Spectrometry: Mechanistic Studies Indicating How a Change in Solvent Conditions and pH Can Dramatically Alter CID Spectra" J. Org. Chem. 67(11); 3693-3699 (2002).
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