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UBC Theses and Dissertations

Development of a novel liquid chromatography based tool to study post-translational modifications Lam, Wing Kai Edgar

Abstract

There are many tools available for the study of post-translational modifications. The majority of these tools is specific towards the individual modification and involves separation of modified proteins from non-modified ones. The drawback of using a modification specific method is that there is a lack of flexibility in its usage for other modifications. The goal of these studies was to investigate the possibility of obtaining a similar separation effect by fractionating post-translationally modified proteins based on the physical properties of proteins. The post-translational modification chosen to be the basis of this study was the O-GlcNAc modification. Using the C2C12 mouse myoblast cell line, it was determined that the optimal conditions for producing lysates containing increased yields of O-GlcNAc modified proteins was to treat differentiated C2C12 cells with 10nM insulin, 12g/L glucose and 2mM of the O-GlcNAcase inhibitor Streptozotocin for 24 hours. Using the optimized lysis buffer, it was shown that protein separation by surface charge using standard anion exchange separation did not provide enough resolution or material to obtain any identifications of modified proteins. However, when a chromatofocusing method which separates proteins on the basis of their isoelectric points was used, a separation scheme with larger capacity and higher resolution was possible. Using this separation method followed by gel electrophoresis of individual fractions, proteins which are potentially O-GlcNAc modified were identified by mass spectrometry. It was evident from the number of protein bands observed per fraction on the Coomassie stained gels and the number of proteins identified per protein band by mass spectrometry that further reduction in sample complexity was required to assist in the positive identification of O-GlcNAc modified proteins. Among the identified proteins, 32 percent were metabolic proteins, 21 percent were protein processing proteins, 16 percent were structural proteins and the remainder a mix of other proteins. Unfortunately, it was not possible to validate the presence or absence of the O-GlcNAc modification on these proteins using available methodologies such as immunoprecipitation. As such, further work is required to optimize the separation strategy and to verify the usefulness of this separation strategy in identifying O-GlcNAc/post-translationally modified proteins.

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