Document Type



Doctor of Philosophy (PhD)



First Advisor's Name

Yuk-Ching Tse-Dinh

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Xiaotang Wang

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Yuan Liu

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Watson Lees

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

Kalai Mathee

Fifth Advisor's Committee Title

Committee Member


Biochemistry, Molecular Biology, Biophysics

Date of Defense



The enzyme DNA topoisomerase I is an essential enzyme that plays an important role in eukaryotic and prokaryotic cellular processes such as DNA replication, transcription, recombination and repair. Mycobacterium tuberculosistopoisomerase I (MtTOP1) is a validated drug target for antituberculosis treatment. Mycobacterial topoisomerase I regulates the topological constraints in chromosomes and helps in maintaining the growth of mycobacteria. The N- terminal domain (NTD) of mycobacterial topoisomerase I contains conserved catalytic domains that along with the active site Tyrosine are involved in cleaving and rejoining a single strand of DNA. Magnesium is required in DNA cleavage activity of type IA topoisomerases. The C-terminal domain (CTD) of mycobacterial topoisomerase I is divided into four subdomains (D5-D8) and a positively charged tail. Each subdomain has a GxxGPY sequence motif. The DNA binding, relaxation, cleavage, religation, catenation and decatenation ability of each subdomains of CTD were studied. The present study shows that each subdomain has its own characteristics. Subdomain D8 and D7 are responsible for maintaining the relaxation activity of mycobacterial topoisomerase I. Subdomain D5 is essential to maintain the DNA cleavage, religation, catenation and decatenation activity. A new crystal structure of MtTOP1-704t (amino acids A2-T704 containing NTD+D5 domains) was obtained. Structures with ssDNA substrate bound to the active site (Y342) in the presence and absence of Mg2+ were also investigated. Significant enzyme conformational changes upon DNA binding place the catalytic tyrosine in a pre-transition position for cleavage of a specific phosphodiester linkage to form a covalent intermediate. Meanwhile, the enzyme/DNA complex with Mg2+ bound at active site may present the post- transition state for religation in the enzyme’s multiple-state DNA relaxation activity. The critical function of a strictly conserved glutamic acid in acid-base catalysis of the DNA cleavage step was also demonstrated by site-directed mutagenesis. The present work provides new functional insights into the more stringent requirement for DNA rejoining versus cleavage by type IA topoisomerase, and further establishes the potential for select interference of DNA rejoining via specific inhibitors.



Files over 15MB may be slow to open. For best results, right-click and select "Save as..."



Rights Statement

Rights Statement

In Copyright. URI:
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).