title: Structural comparison of the free and DNA-bound forms of the purine repressor DNA-binding domain.
abstract: BACKGROUND
  The purine repressor (PurR) regulates genes that encode enzymes for purine biosynthesis. PurR has a two domain structure with an N-terminal DNA-binding domain (DBD) and a C-terminal corepressor-binding domain (CBD). The three dimensional structure of a ternary complex of PurR bound to both corepressor and a specific DNA sequence has recently been determined by X-ray crystallography.
  
  
  RESULTS
  We have determined the solution structure of the PurR DBD by NMR. It contains three helices, with the first and second helices forming a helix-turn-helix motif. The tertiary structure of the three helices is very similar to that of the corresponding region in the ternary complex. The structure of the hinge helical region, however, which makes specific base contacts in the minor groove of DNA, is disordered in the DNA-free form.
  
  
  CONCLUSIONS
  The stable formation of PurR hinge helices requires PurR dimerization, which brings the hinge regions proximal to each other. The dimerization of the hinge helices is likely to be controlled by the CBD dimerization interface, but is induced by specific-DNA binding.
authors.affiliation: Graduate School of Integrated Science, Yokohama City University, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Nagadoi
authors.forename: S
authors.initials: S
authors.lastname: Morikawa
authors.forename: H
authors.initials: H
authors.lastname: Nakamura
authors.forename: M
authors.initials: M
authors.lastname: Enari
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
authors.forename: H
authors.initials: H
authors.lastname: Yamamoto
authors.forename: G
authors.initials: G
authors.lastname: Sampei
authors.forename: K
authors.initials: K
authors.lastname: Mizobuchi
authors.forename: M A
authors.initials: MA
authors.lastname: Schumacher
authors.forename: R G
authors.initials: RG
authors.lastname: Brennan
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D019077:Helix-Turn-Helix Motifs; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009875:Operator Regions, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; C065825:PurR protein, Bacteria; C489317:PurR protein, E coli; D012097:Repressor Proteins