Human tryptophan dioxygenase (hTDO) is an important hemeprotein that catalyzes the initial and rate-limiting step of the kynurenine (KYN) pathway-the conversion of Trp to N-formyl kynurenine (NFK). It is well-accepted that hTDO plays a critical role in controlling Trp homeostasis in liver. More recently, it was discovered tha hTDO is also expressed in a variety of human tumors to suppress antitumor immunity, thereby promoting aggressive tumor growth. In addition to cancer, hTDO has been implicated in a wide spectrum of neurodegenerative diseases, such as Alzheimer's and Huntington's diseases, as well as depression. hTDO has hence been recognized as an important therapeutic target. Despite its importance, the progress has been limited by the poor knowledge of the molecular properties of the enzyme. Recently, we have made several major breakthroughs in (i) developing a new protocol allowing the preparation of high quality hTDO protein, allowing the documentation of the first glimpse of the structural features critical for the dioxygenase chemistry, as well as an unusual activity of the ferric enzyme, (ii) solving the first substrate-bound 3D-structure of hTDO, as well as trapping reaction intermediates in single crystals and solved their structures, which unveiled several previously unidentified structural features that ar critical for controlling the catalytic activity and cellular degradation of the enzyme, one of the most rapidly degraded enzymes in liver, and (iii) obtaining the first evidence supporting the cellular degradation of hTDO via a ubiquitination-linked proteasomal degradation pathway. These important achievements allow us to build novel hypotheses and propose a comprehensive approach from a unique perspective to test them. The main objective of this project is to delineate the structure, function and regulation of hTDO, as part of our long term goal in comprehending heme dioxygenase chemistry and TDO biology.
The specific aims of our project are: (i) identify the novel dioxygenase intermediates of hTDO. (ii) Determine the dioxygen activation mechanism of the unique ferric reaction. (iii) Delineate the product release mechanism of hTDO. (iv) Delineate the exosite-dependent regulation mechanisms of hTDO. We anticipate that fulfilling the objectives of this project will result in new insights into the struture, function and regulation of this essential enzyme, and provide an important blueprint for the design of hTDO-selective inhibitors as therapeutics for cancer, neurodegenerative diseases and depression.
The proposed studies are focused on determining the catalytic and regulatory mechanisms of a human hepatic enzyme, tryptophan dioxygenase (hTDO), an important yet poorly understood enzyme, which plays essential roles in maintaining tryptophan homeostasis and in suppressing antitumor immunity and supporting tumor growth. The proposed research is relevant to public health, because a comprehensive understanding of the structure, function and regulation of hTDO should provide a foundation for the development of hTDO-selective inhibitors for therapeutic intervention against cancer, neurodegenerative diseases and depression.
|Lewis-Ballester, Ariel; Pham, Khoa N; Batabyal, Dipanwita et al. (2017) Structural insights into substrate and inhibitor binding sites in human indoleamine 2,3-dioxygenase 1. Nat Commun 8:1693|
|Uchida, Takeshi; Sekine, Yukari; Dojun, Nobuhiko et al. (2017) Reaction intermediates in the heme degradation reaction by HutZ from Vibrio cholerae. Dalton Trans 46:8104-8109|
|Glass, Lisa N; Swapna, Ganduri; Chavadi, Sivagami Sundaram et al. (2017) Mycobacterium tuberculosis universal stress protein Rv2623 interacts with the putative ATP binding cassette (ABC) transporter Rv1747 to regulate mycobacterial growth. PLoS Pathog 13:e1006515|
|Ishigami, Izumi; Zatsepin, Nadia A; Hikita, Masahide et al. (2017) Crystal structure of CO-bound cytochrome c oxidase determined by serial femtosecond X-ray crystallography at room temperature. Proc Natl Acad Sci U S A 114:8011-8016|
|Lewis-Ballester, Ariel; Forouhar, Farhad; Kim, Sung-Mi et al. (2016) Molecular basis for catalysis and substrate-mediated cellular stabilization of human tryptophan 2,3-dioxygenase. Sci Rep 6:35169|
|Nelson, Garrett; Kirian, Richard A; Weierstall, Uwe et al. (2016) Three-dimensional-printed gas dynamic virtual nozzles for x-ray laser sample delivery. Opt Express 24:11515-30|
|Batabyal, Dipanwita; Lewis-Ballester, Ariel; Yeh, Syun-Ru et al. (2016) A Comparative Analysis of the Effector Role of Redox Partner Binding in Bacterial P450s. Biochemistry 55:6517-6523|
|Álvarez, Lucía; Lewis-Ballester, Ariel; Roitberg, Adrián et al. (2016) Structural Study of a Flexible Active Site Loop in Human Indoleamine 2,3-Dioxygenase and Its Functional Implications. Biochemistry 55:2785-93|