Proteomic Analysis of the Flavonoid Biosynthetic Machinery in Arabidopsis Thaliana
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PROTEOMIC ANALYSIS OF THE FLAVONOID BIOSYNTHETIC MACHINERY IN ARABIDOPSIS THALIANA Nileshwari N. Vaghela Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in the partial fulfillment of the requirement for the degree of Master of Science in Biological Sciences Brenda S.J. Winkel, Ph.D., Committee Co-chair Iuliana M. Lazar, Ph.D., Committee Co-chair Richard F. Helm, Ph.D., Committee Member Richard A. Walker, Ph.D., Committee Member August 28, 2007 Blacksburg, Virginia Keywords: Protein-protein interactions, Enzyme complexes, Affinity chromatography, Flavonoid pathway, Mass spectrometry, Proteomics Copyright 2007, Nileshwari N. Vaghela PROTEOMIC ANALYSIS OF FLAVONOID BIOSYNTHETIC MACHINERY IN ARABIDOPSIS THALIANA Nileshwari N. Vaghela Abstract Work on a wide variety of metabolic pathways indicates that these systems are often, if not always, organized as multienzyme complexes. Enzyme complexes have the potential to increase catalytic efficiency and provide unique mechanisms for the regulation of cellular metabolism. The flavonoid biosynthetic pathway of Arabidopsis is an excellent model for studying the organization, localization, and regulation of enzyme complexes at the cellular level. Flavonoids are specialized metabolites that perform many important physiological roles in plants. Protein interactions among several key flavonoid enzymes have been described. Moreover, at least two of the flavonoid enzymes have a dual cytoplasmic/nuclear localization. These results indicate that flavonoid enzymes assemble into one or more distinct complexes at different intracellular locations. The current study integrates a new technology, mass spectrometry, with well-established affinity chromatography methods to further characterize the organization and composition of the Arabidopsis flavonoid enzyme complex. One of the key flavonoid enzymes, chalcone isomerase (CHI), was used in these experiments to detect interacting enzymes. Recombinant thioredoxin (TRX), or TRX-CHI, was produced in E. coli , then purified by metal affinity chromatography, and covalently coupled to an activated resin, Affi-Gel 10. Extracts prepared from 4-day-old wild type or CHI-deficient lines of Arabidopsis were then passed over the column and the bound proteins eluted with sodium dedocyl sulfate (SDS). This eluate was then subjected to a liquid chromatography (LC) - mass spectrometry (MS) protocol developed for the analysis of complex peptide mixtures. An Agilent LC system coupled with an LTQ-MS instrument (Thermo Electron, San Jose, CA) was used for this purpose. Data analysis was performed with the Bioworks software package. Different optimization strategies were performed to improve the affinity chromatography, sample preparation, and the LC separation method. A novel approach has been developed for the MS analysis of biological samples containing contaminants such as salts and detergents. Protein extracts prepared from wild type Landsburg and mutant tt5 (86) were analyzed by LC-MS/MS. A total of 491 proteins were identified for Landsburg and 633 for tt5 (86) extracts using a combination of data filters and p-value sorting. All detected proteins had p<0.001 and most were identified by at least 2 unique peptides. iii ACKNOWLEDGMENTS I wish to express my deepest gratitude to my mentors, Dr. Brenda S.J. Winkel and Dr. Iuliana M. Lazar, for giving me the opportunity to be part of the fascinating world of science and molecular biology and proteomics research. I thank them for encouraging me in many aspects of my research project, from challenging me in developing ideas, planning and executing experiments, to interpreting and presenting results. I would like to extend my thanks to my committee members, Dr. Richard F. Helm and Dr. Richard A. Walker for their time, contributions, and recommendations. I appreciate their willingness to serve on my research committee. My sincere thanks to my fellow lab mates in the Winkel laboratory, Melissa Ramirez, Jonathan Watkinson, Peter Bowerman, and Kevin Crosby, for their cheerful team spirit and support. In addition, I would also like to thank Hetal Sarvaiya and Dr. Jung Hae Yoon for their help with mass spectrometric research. My deepest gratitude belongs to my family for being endlessly supportive and caring. My sister-in-law, Nirali for helping me and motivating during my graduate career. I would like to thank my husband, Nishant for always believing in me and helping me reach my goals. Without him I would not be where I am today. This work is dedicated to him. iv A special thanks to my friend, Dr. Margret S. Rodrigues, for her help in reviewing my thesis and motivating me to reach my goal. v CONTENTS ACKNOWLEDGMENTS ................................................................................................. iv TABLE OF CONTENTS................................................................................................... vi LIST OF FIGURES ......................................................................................................... viii LIST OF TABLES.............................................................................................................. x Chapter 1 : Introduction ......................................................................................................1 Multienzyme Complexes .....................................................................................................2 The Flavonoid Biosynthetic Pathway of Arabidopsis thaliana ...........................................2 Mass Spectrometry...............................................................................................................6 Protein Profiling by Mass Spectrometry............................................................................10 Protein-Protein Interactions and Proteomics .....................................................................10 Proposed Study ..................................................................................................................12 Acknowledgments..............................................................................................................13 Chapter 2 : Proteomic Analysis of the Flavonoid Biosynthetic Machinery of Arabidopsis thaliana .............................................................................................................14 Summary............................................................................................................................15 Introduction........................................................................................................................16 Materials and Methods.......................................................................................................18 Results................................................................................................................................20 Discussion..........................................................................................................................23 Acknowledgment ...............................................................................................................23 vi Chapter 3 : Mass Spectrometric Analysis of Recombinant Proteins, Affinity Eluted Samples, and Soluble Plant Extracts From Wild Type Landsburg Ecotype and Mutant tt5 (86) Arabidopsis thaliana .........................................................................................................24 Summary............................................................................................................................25 Introduction........................................................................................................................26 Materials and Methods.......................................................................................................27 Results................................................................................................................................31 Discussion..........................................................................................................................51 Acknowledgments..............................................................................................................52 Chapter 4 : Conclusions ....................................................................................................53 Conclusions........................................................................................................................54 References..........................................................................................................................56 Appendix A: Results from proteomic analysis of Landsburg seedlings............................68 VITA..................................................................................................................................79 vii List of Figures Chapter 1 Figure 1.1 Phenotypic changes induced by transparent testa (tt ) mutation. .......................4 Figure 1.2 Schematic of the flavonoid pathway of Arabidopsis.........................................5 Figure 1.3 Schematic representation of the main processes occurring within a mass spectrometer. ..........................................................................................8 Figure 1.4 Outline of the protein identification process. ....................................................9 Chapter 2 Figure 2.1 Schematic diagram of experimental steps performed for affinity chromatography and mass spectrometry..........................................................17