Kinetic partitioning between alternative protein-protein interactions controls a transcriptional switch.
Proteins can perform completely distinct functions in response to the particular partners that they bind to. Consequently, determination of the mechanism of functional regulation in such systems requires elucidation of the mechanism switching between binding partners. The central protein of the Escherichia coli biotin regulatory system, BirA, switches between its function as a metabolic enzyme or a transcriptional repressor in response to binding either the biotin carboxyl carrier protein subunit of acetyl-CoA carboxylase or a second BirA monomer. These two protein-protein interactions are structurally mutually exclusive. The results of earlier studies suggest that the system is regulated by kinetic partitioning between the two protein-protein interactions. In this work, sedimentation velocity was employed to monitor the partitioning directly. The results indicate similar equilibrium parameters governing formation of the two protein-protein interactions. Kinetic analysis of the sedimentation velocity data indicated that holoBirA dimerization is governed by very slow forward and reverse rate constants. The slow kinetics of holoBirA dimerization combined with fluctuations in the intracellular apoBCCP pool are critical determinants in partitioning BirA between its distinct biological functions.
Department of Chemistry and Biochemistry, Center for Biological Structure and Organization, University of Maryland, College Park, MD 20742, USA.
Huaying
H
Zhao
Dorothy
D
Beckett
D000255:Adenosine Triphosphate / Q000378:metabolism; D001710:Biotin / Q000378:metabolism; D019731:Carbon-Nitrogen Ligases / Q000235:genetics* / Q000378:metabolism*; D002384:Catalysis; D002498:Centrifugation; D018983:DNA Footprinting; D003851:Deoxyribonucleases / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D007700:Kinetics; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism*; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic
D029968:Escherichia coli Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D001710:Biotin; D000255:Adenosine Triphosphate; D003851:Deoxyribonucleases; D019731:Carbon-Nitrogen Ligases; C058125:birA protein, E coli