title: The biotin regulatory system: kinetic control of a transcriptional switch.
abstract: An organism's response to environmental and metabolic cues requires communication between transcription regulatory processes and "other" cellular events. In a number of biological control circuits, the communication is carried out by a single multifunctional protein that participates directly in transcription initiation and in at least one other cellular process. Structural studies suggest that the function of these proteins is dictated by the formation of mutually exclusive protein-protein interactions. However, the rules that govern partner, and thus functional switching, are not known. In the Escherichia coli Biotin Regulatory System, the bifunctional protein, BirA, catalyzes post-translational biotin addition to a biotin-dependent carboxylase and binds sequence-specifically to DNA to repress transcription initiation at the biotin biosynthetic operon. Previous structural and modeling studies suggest that BirA function is determined by formation of alternative homo- and heterodimeric protein-protein interactions. In this work, the BirA functional switch is investigated using DNaseI footprinting and MALDI-TOF mass spectrometry. Results of these measurements indicate that BirA can be selectively targeted toward its enzymatic function simply by increasing the kinetic probability of heterodimerization relative to that of homodimerization. Subsequent shifting to the DNA binding function occurs as the pool of heterodimer partner is depleted and homodimerization dominates. The data support a switching mechanism in which BirA's function is dictated by its probability of encountering a particular protein partner.
authors.affiliation: Department of Chemistry and Biochemistry and Center for Biological Structure and Organization, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Emily D
authors.initials: ED
authors.lastname: Streaker
authors.forename: Dorothy
authors.initials: D
authors.lastname: Beckett
mesh_terms: D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D001059:Apoproteins / Q000235:genetics / Q000378:metabolism; D001710:Biotin / Q000235:genetics / Q000378:metabolism*; D019731:Carbon-Nitrogen Ligases / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002384:Catalysis; D018983:DNA Footprinting; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D054889:Fatty Acid Synthase, Type II; D015964:Gene Expression Regulation, Bacterial; D007700:Kinetics; D008954:Models, Biological; D011485:Protein Binding; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001059:Apoproteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D021122:Protein Subunits; D012097:Repressor Proteins; D014157:Transcription Factors; D001710:Biotin; D054889:Fatty Acid Synthase, Type II; D019731:Carbon-Nitrogen Ligases; C058125:birA protein, E coli; D000103:Acetyl-CoA Carboxylase; C079633:biotin carboxyl carrier protein