Protein tyrosine phosphatase 1B (PTP1B) is a validated drug target, but it has proven difficult to develop medicinally useful, reversible inhibitors of this enzyme. Here we explored covalent strategies for the inactivation of PTP1B using a conjugate composed of an active site-directed 5-aryl-1,2,5-thiadiazolidin-3-one 1,1-dioxide inhibitor connected via a short linker to an electrophilic α-bromoacetamide moiety. Inhibitor-electrophile conjugate 5a caused time-dependent loss of PTP1B activity consistent with a covalent inactivation mechanism. The inactivation occurred with a second-order rate constant of (1.7 ± 0.3) × 10 M min. Mass spectrometric analysis of the inactivated enzyme indicated that the primary site of modification was C121, a residue distant from the active site. Previous work provided evidence that covalent modification of the allosteric residue C121 can cause inactivation of PTP1B [Hansen, S. K., Cancilla, M. T., Shiau, T. P., Kung, J., Chen, T., and Erlanson, D. A. (2005) Biochemistry 44, 7704-7712]. Overall, our results are consistent with an unusual enzyme inactivation process in which noncovalent binding of the inhibitor-electrophile conjugate to the active site of PTP1B protects the nucleophilic catalytic C215 residue from covalent modification, thus allowing inactivation of the enzyme via selective modification of allosteric residue C121.

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I deeply appreciate all his knowledge, scientific attitude as well as opportunity to improve myself in order to become an excellent scientist. I always admire his love and passion of science that will always be an example of scientist in the next generation. I also would like to thank my committee members Dr. Michael Harmata, Dr.Paul Sharp, and Dr.Xiaoqin Zou for their valuable time and support. I would like to thank all my co-workers for their time as friends, colleagues, and trainers. Especially, Nicholas Santo and Kasi Viswanatha Raju Ruddraraju who always motivate me to move forward even during the time of difficulty. Another important group of people who play an important role in my life here are CCH and CRU people. They have always been such a great help not only my career but also my life in the US. To my best friends, Andrew White, Marc Ehlers, Ryan Buttrey, and Rebecca Beckham who always understand and give me heartfelt help and support. Thanks for always be there when I need someone. I also would like to thank David Sower as a teacher, a mentor, and a friend who has been praying and offering deeply sincere motivation. (Happy for Ryan and Rebecca, they are getting married!) Lastly, mom and dad have been of great moral support to me all throughout my life miles away from home. For three years, they have provided strength and perseverance to pursue Ph.D. Without them, this work would have not been successful. I will always love you two.