title: Intermolecular Interactions of Cardiac Transcription Factors NKX2.5 and TBX5.
abstract: Heart development in mammalian systems is controlled by combinatorial interactions of master cardiac transcription factors such as TBX5 and NKX2.5. They bind to promoters/enhancers of downstream targets as homo- or heteromultimeric complexes. They physically interact and synergistically regulate their target genes. To elucidate the molecular basis of the intermolecular interactions, a heterodimer and a homodimer of NKX2.5 and TBX5 were studied using X-ray crystallography. Here we report a crystal structure of human NKX2.5 and TBX5 DNA binding domains in a complex with a 19 bp target DNA and a crystal structure of TBX5 homodimer. The ternary complex structure of NKX2.5 and TBX5 with the target DNA shows physical interactions between the two proteins through Lys158 (NKX2.5), Asp140 (TBX5), and Pro142 (TBX5), residues that are highly conserved in TBX and NKX families across species. Extensive homodimeric interactions were observed between the TBX5 proteins in both crystal structures. In particular, in the crystal structure of TBX5 protein that includes the N-terminal and DNA binding domains, intermolecular interactions were mediated by the N-terminal domain of the protein. The N-terminal domain of TBX5 was predicted to be "intrinsically unstructured", and in one of the two molecules in an asymmetric unit, the N-terminal domain assumes a β-strand conformation bridging two β-sheets from the two molecules. The structures reported here may represent general mechanisms for combinatorial interactions among transcription factors regulating developmental processes.
authors.affiliation: Department of Bioengineering, University of Texas at Dallas , Richardson, Texas 75080, United States.
authors.forename: Lagnajeet
authors.initials: L
authors.lastname: Pradhan
authors.affiliation: Department of Bioengineering, University of Texas at Dallas , Richardson, Texas 75080, United States.
authors.forename: Sunil
authors.initials: S
authors.lastname: Gopal
authors.affiliation: Department of Bioengineering, University of Texas at Dallas , Richardson, Texas 75080, United States.
authors.forename: Shichang
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Bioengineering, University of Texas at Dallas , Richardson, Texas 75080, United States.
authors.forename: Shayan
authors.initials: S
authors.lastname: Ashur
authors.affiliation: Department of Bioengineering, University of Texas at Dallas , Richardson, Texas 75080, United States.
authors.forename: Saai
authors.initials: S
authors.lastname: Suryanarayanan
authors.affiliation: Department of Functional Genomics, University of Florida , Gainesville, Florida 32610, United States.
authors.forename: Hideko
authors.initials: H
authors.lastname: Kasahara
authors.affiliation: Department of Bioengineering, University of Texas at Dallas , Richardson, Texas 75080, United States.
authors.forename: Hyun-Joo
authors.initials: HJ
authors.lastname: Nam
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D006321:Heart; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020825:T-Box Domain Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; C095552:NKX2-5 protein, human; D020825:T-Box Domain Proteins; C103172:T-box transcription factor 5; D014157:Transcription Factors