title: The crystal structure of trp aporepressor at 1.8 A shows how binding tryptophan enhances DNA affinity.
abstract: Comparison of the crystal structure of inactive unliganded trp aporepressor with that of trp repressor shows that binding tryptophan activates the dimer a thousandfold by moving two symmetrically-disposed flexible bihelical motifs. These flexible 'DNA-reading heads' flank a highly inflexible core domain formed by an unusual arrangement of interlocking alpha-helices from both subunits.
mesh_terms: D001059:Apoproteins / Q000378:metabolism*; D001426:Bacterial Proteins; D001665:Binding Sites; D004247:DNA / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D011487:Protein Conformation; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014364:Tryptophan
chemical_list: D001059:Apoproteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; C027190:TRPR protein, E coli; D014157:Transcription Factors; D014364:Tryptophan; D004247:DNA