title: Dimerization of the Escherichia coli biotin repressor: corepressor function in protein assembly.
abstract: The repressor of biotin biosynthesis binds to the biotin operator sequence to repress transcription initiation at the biotin biosynthetic operon. Site-specific binding of BirA to the biotin operator is allosterically regulated by binding of the small molecule, biotinyl-5'-adenylate (bio-5'-AMP). The operator is a 40 base pair imperfect inverted palindrome and two holorepressor monomers bind cooperatively to the two operator half-sites. Results of previous detailed analyses of binding of holoBirA to bioO indicate that site-specific DNA binding and protein dimerization are obligatorily linked in the system. In the present work equilibrium sedimentation measurements have been used to examine the assembly properties of the aporepressor and its complexes with small ligands biotin and bio-5'-AMP. Results of these measurements indicate that while the free protein and the biotin complex exhibit no tendency to self-associate, the adenylate-bound protein assembles into dimers with an equilibrium constant of 11 microM. The results suggest that one mechanism by which the adenylate promotes binding of BirA to the biotin operator is by promoting repressor dimerization.
authors.affiliation: Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, National Institute of Standards and Technology, Rockville 20850, USA.
authors.forename: E
authors.initials: E
authors.lastname: Eisenstein
authors.forename: D
authors.initials: D
authors.lastname: Beckett
mesh_terms: D000249:Adenosine Monophosphate / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D001051:Apoenzymes / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D001710:Biotin / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D019731:Carbon-Nitrogen Ligases / Q000737:chemistry / Q000378:metabolism; D004269:DNA, Bacterial / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins; D020035:Holoenzymes / Q000737:chemistry / Q000378:metabolism; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D011499:Protein Processing, Post-Translational; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D014157:Transcription Factors; D014461:Ultracentrifugation
chemical_list: C082099:5'-AMP-biotin; D001051:Apoenzymes; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D020035:Holoenzymes; D046911:Macromolecular Substances; D012097:Repressor Proteins; D014157:Transcription Factors; D000249:Adenosine Monophosphate; D001710:Biotin; D019731:Carbon-Nitrogen Ligases; C058125:birA protein, E coli