Physico-chemical characterization of the interaction between thyroid transcription factor 1 (TTF-1) and DNA

The thyroid transcription factor 1 (TTF-1) is a tissue-specific transcription factor involved in the development of thyroid and lung. It is a protein of 371 amino acids that possesses two independent transcriptional activation domains, one located in the N-terminal region of homeodomain and the other in the C-terminal region. The homeodomain is a highly conserved DNA-binding motif that is found in numerous transcription factors throughout a large variety of species from yeasts to human. These gene-specific transcription factors play critical roles in development and adult homeostasis, and therefore, any germline mutations associated with these proteins can lead to a number of congenital abnormalities. Remarkable features of structural and functional conservation have been observed within homeodomain family members. This high degree of conservation between the sequence and structure makes the homeodomain an ideal model for studying protein-DNA interactions and gene regulation. In this PhD thesis, the study on the conformational stability and DNA binding energetics of the rat thyroid transcription factor 1 homeodomain (TTF-1HD) is reported. Furthermore, to gain a molecular-level understanding of the interactions determining the association of TTF-1HD to the target DNA sequence, Some key point mutants (W48, Q50 and Y54) and a deletion mutant (desTTF-1HD), lacking five residues from the N-terminal region have been produced and studied. Since it has been demonstrated that N-terminal region of TTF-1 also interact with Pax-8 (transcription factor belonging to the PAX genes superfamily) in the regulation of thyroid-specific gene expression, the study of the thermal stability and DNA binding energetics of a fusion protein, containing the N-terminal region and the homeodomain of TTF-1 (TTF-1NH2HD), and a recombinant protein containing C-terminal region of Pax-8 (Pax-8 Prd) has been reported.