The Structural Basis For The Specific DNA Recognition Of Transcriptional Factor SATB1

SATB1(special AT-rich binding protein1) is essential for thymus development and T-cell maturation, and can promoter multi-type tumors growth and metastasis by acting as a global chromatin organizer and gene expression regulator in eukaryotic cells. SATB1can bind AT-rich MAR/BUR (matrix attachment region/base-unpairing region) sequence in genes promoters and regulatory elements, and anchor these DNA targets to nuclear matrix. By this way, SATB1organizes high-order architecture of chromatin and thereby regulates the global genes expression in eukaryotic cells.However, as a key transcriptional factor and scaffold protein, the DNA binding mechanism of SATB1is unclear. Additionally, the self-association of SATB1is very important for the DNA binding of SATB1, and the mechanism by which SATB1oligomerizes also remains elusive. In this dissertation, we studied the oligomerization and DNA-binding of SATB1by menthods of structural biology and biochemistry.In the first part, we determined the crystal structure of the N-terminal oligomeriztion domain of SATB1. Surprisingly, this domain resembles a ubiquitin domain instead of the previously proposed PDZ domain, and this newly defined domain was named as ULD (ubiquitin-like domain). Biochemical studies reveal that SATB1can form a tetramer through ULD in solution. The tetramerization of SATB1plays an essential role in its binding to highly specialized DNA sequences. Furthermore, isothermal titration calorimetry results indicate that the SATB1tetramer can bind simultaneously to two DNA targets. Based on these results, we propose a molecular model that SATB1regulates the expression of eukaryotic genes by orginazing high-order chromatin architecture. In this model, SATB1directly binds MAR/BUR sequence in genes promoters to regulate local genes expression, or mediates the formation of chromatin loop to coordinate multiple genes expression at a distance. And in the second part, we report the crystal structure of the N-terminal module of SATB1. Interestingly, this module contains a ULD and a novel CUT domain. And the novel CUT domain was named as CUTL (CUT-like domain). Detailed biochemical experiments indicate that the N-terminus of SATB1(residues1-248, SATB1(1-248)) including the extremely N-terminal70amino acids and the ULD-CUTL tandem binds specifically to DNA target. Our results show that the DNA-binding ability of full-length SATB1require the contribution of CUTL domain, as well as the CUT1-CUT2tandem and HD domains. These findings may reveal a multiple-domains coordinated mechanism whereby SATB1recognizes DNA targets.In the last part, we assembled the complex of full-length SATB1with specific DNA. Preliminary biochemical and structural studies were performed on this complex. In future, we will try to determine the3D structure of the SATB1-DNA complex and reveal the detailed mechanism whereby SATB1binds DNA targets.Taken together, based on these stuctural and biochemical studies, we redefined the domain constitution of SATB1and proposed a molecular model whereby SATB1binds DNA targets.