Protein-Protein Interactions Dominate the Assembly Thermodynamics of a Transcription Repression Complex

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• 作者：Huaying Zhao ; Emily Streaker ; Weilan Pan ; Dorothy Beckett
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：November 27, 2007
• 年：2007
• 卷：46
• 期：47
• 页码：13667 - 13676
• 全文大小：243K
• 年卷期：v.46,no.47(November 27, 2007)
• ISSN：1520-4995

文摘

Assembly of the transcription repression complex at the Escherichia coli biotin biosyntheticoperon occurs via coupled protein-protein and protein-DNA interactions in which the holoBirA dimerbinds to the forty base pair biotin operator sequence. The thermodynamic driving forces for the assemblyprocess have been dissected using sedimentation equilibrium measurements and DNaseI footprint titrations.Measurements of the temperature dependence of dimerization indicate that this process is stronglyenthalpically opposed and is driven by a very favorable entropy. By contrast, the DNA binding step isenthalpically driven and opposed by a modest entropy. Neither step is accompanied by a heat capacitychange. The convoluted protein-protein and protein-DNA binding reaction is dominated by thethermodynamic signature of the dimerization step. This observed dominance of the dimerization stepillustrates the importance of dissecting complex DNA binding reactions into their constituent steps inelucidation of the thermodynamic driving forces for these processes. Measurements of the salt dependenceof dimerization and DNA binding indicate modest contributions of electrostatic interactions to eachcontributing step as well as the total assembly of the repression complex. In light of the known structuralfeatures of this system, this modest dependence of the DNA binding equilibrium on salt concentrationwas unanticipated.