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Characterization of Glycation Sites on Human Serum Albumin Using Mass Spectrometry University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Student Research Projects, Dissertations, and Theses - Chemistry Department Chemistry, Department of 4-2010 Characterization of Glycation Sites on Human Serum Albumin using Mass Spectrometry Omar S. Barnaby University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/chemistrydiss Part of the Analytical Chemistry Commons, and the Biochemistry Commons Barnaby, Omar S., "Characterization of Glycation Sites on Human Serum Albumin using Mass Spectrometry" (2010). Student Research Projects, Dissertations, and Theses - Chemistry Department. 8. https://digitalcommons.unl.edu/chemistrydiss/8 This Article is brought to you for free and open access by the Chemistry, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Student Research Projects, Dissertations, and Theses - Chemistry Department by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. CHARACTERIZATION OF GLYCATION SITES ON HUMAN SERUM ALBUMIN USING MASS SPECTROMETRY by Omar St. Aubyn Barnaby A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy Major: Chemistry Under the Supervision of Professor David S. Hage Lincoln, Nebraska April, 2010 CHARACTERIZATION OF GLYCATION SITES ON HUMAN SERUM ALBUMIN USING MASS SPECTROMETRY Omar S. Barnaby, Ph.D. University of Nebraska, 2010 Advisor: David S. Hage The modification of proteins by reducing sugars is a process that occurs naturally in the body. This process, which is known as glycation, has been linked to many of the chronic complications encountered during diabetes. Glycation has also been linked to changes in the binding of human serum albumin (HSA) to several drugs and small solutes in the body. While these effects are known, there is little information that explains why these changes in binding occur. The goal of this project was to obtain qualitative and quantitative information about glycation that occurs on HSA. The first section of this dissertation examined methods that could be used to quantify and identify glycation that occurs on HSA. The extent of glycation that occurred on HSA was quantified using 18 O-labeling mass spectrometry and the glycation sites were identified by observing the mass-to-charge (m/z) shifts that occurred in glycated HSA. This initial investigation revealed that 18 O-labeling based quantitation can be improved over previous methods if a relative comparison is done with 18 O-labeled peptides in a control HSA sample. Similarly, the process of making m/z shift-based assignments could be improved if only the peptides that were unique to the glycated HSA samples were used with internal calibration. These techniques were used in subsequent chapters for the assignment of early and late-stage glycation products on HSA. The regions on HSA that contained the highest amount of modification were identified, quantified, and ranked in order of their relative abundance. Of the commonly reported glycation sites, the N-terminus was found to have the highest extent of modification, followed by lysines 525, 199, and 439. The relative amount of modification on lysine 281, with respect to the aforementioned residues, varied with different degrees of glycation. The 18 O approach used for this analysis was novel because it allowed for the simultaneous quantification of all glycation-related modifications that were occurring on HSA. As such, several arginine residues were also found to have high amounts of modification on glycated HSA. iv Dedication The work in this dissertation is dedicated to my mother, Paulette, my late-father, Christopher; and to my brothers, Tion, Olu, and Christopher. The love and support that they have given to me cannot be described in words. I love them dearly and appreciate the many sacrifices that they have made on my behalf. I also dedicate this work to the younger ones in my family. Let this be a constant reminder that hard work and dedication in anything that you pursue does not go unnoticed. Strive for the best in whatever you do and success will surely follow. v Acknowledgements I would like to thank my faculty advisor, Professor David S. Hage for his support and guidance during my time at UNL. His organization, drive for developing novel ideas, and approach to high quality research has always been an inspiration for me, and his willingness to support my ideas played a large role in my development as a scientist. I would also like to thank the professors my supervisory committee, Jody Redepenning, Anu Subramanian, Barry Cheung, and the late Adrian George. Their guidance played a major role in the development of my critical thinking skills and my ability to see the “big picture” when it comes to scientific research. I would like to thank the researchers at the Nebraska Center for Mass Spectrometry, Ron Cerny and Kurt Wulser, for their support on several topics related to my graduate work. They were instrumental in teaching me the basics of mass spectrometry and providing advice in solving difficult problems that were related to my research. I am also grateful for my many colleagues in the Hage lab. It was a pleasure working with Corey, John, Rangan, Jeanethe, Ankit, Krina, David, Chad, Mia, Tong, Michelle, Abby, and Erica. I value the time that we spent toiling over classes and research, having random lunch time conversations on just about any topic, and having well needed comedic relief at times. I wish you all the best of success in graduate school and in any path that you choose in life. I would also like to extend special thanks to additional family and friends. It was a pleasure collaborating with two of my friends, Ala Qadi and Ufuk Nalbantoglu, on the development of programs that were used for my research. The development of these tools vi allowed me to process data at a rapid rate, and certainly allowed for the early completion of several projects. Special thanks are also in order for my many uncles and aunts, Paul, Annette, Pam, Janet, Madge, Vaughn, Val, Carla, Ruby, Brenton, Doreen, and Babeth; my godmother, Aprylle, and my grandmother, Sylvia. There is no doubt in my mind of their continued support over the years. I am grateful and love them dearly. There is simply not enough room to list the number of people that have not only supported me over the years but have made practical contributions to my success. To my family and friends, your support over the years has made this process an enjoyable one. Thank you! vii Table of Contents Chapter 1: General Introduction 1.A. Effects of diabetes and protein glycation .............................................................1 1.A.1. Classification and effects of diabetes in vivo .....................................................1 1.A.2. Glycation and advanced glycation end products ...............................................2 1.A.3. Early and late stage glycation of HSA ...............................................................6 1.B. Approaches for the analysis of glycated HSA ......................................................9 1.B.1. Prior attempts at determining HSA glycation ....................................................9 1.B.2. Analysis of glycated HSA using MALDI-TOF MS and 18 O labeling .............13 1.B.3. Topics covered in this dissertation ...................................................................14 1.C. References .............................................................................................................18 Chapter 2: Quantitative Analysis of Glycation Sites on Commercially Glycated Human Serum Albumin 2.A. Introduction ..........................................................................................................28 2.B. Experimental .........................................................................................................32 2.B.1. Materials ..........................................................................................................32 2.B.2. Apparatus .........................................................................................................32 2.B.3. Sample pretreatment, digestions, & peptide fractionation ...............................33 2.B.4. Mass spectrometry and data acquisition ..........................................................33 2.B.5. Peak selection criteria and data sorting ...........................................................34 2.C. Results ....................................................................................................................35 2.C.1. Sequence coverage ...........................................................................................35 2.C.2. Measurement of 16 O/ 18 O ratios for peptide digests from glycated HSA .........38 2.C.3. Peptides with high 16 O/ 18 O ratios representing early or advanced glycation products ......................................................................................................................48 2.C.4. Correlation of modifications with local p Ka or FAS values ............................49 2.C.5. Location of modified sites versus major drug binding sites on HSA ..............53 2.C.6. Comparisons of methods 1 and 2 for 16 O/ 18 O determination ...........................54 viii 2.D. Summary ...............................................................................................................56
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