Thermodynamics of nucleotide binding to NBS-I of the Bacillus subtilis preprotein translocase subunit SecA. |
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| Authors: | T den Blaauwen J P van der Wolk C van der Does K H van Wely A J Driessen |
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| Institution: | Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands. |
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| Abstract: | SecA is the dissociatable nucleotide and preprotein binding subunit of the bacterial translocase. The thermodynamics of nucleotide binding to soluble SecA at nucleotide binding site I were determined by isothermal titration calorimetry. Binding of ADP and non-hydrolyzable ATPgammaS is enthalpy-driven (DeltaH(0) of -14.44 and -5.56 kcal/mol, respectively), but is accompanied by opposite entropic contributions (DeltaS(0) of -18.25 and 9.55 cal/mol/K, respectively). ADP binding results in a large change in the heat capacity of SecA (DeltaC(p)=-780 cal/mol/K). It is suggested that ADP binding promotes the interaction between the two thermodynamically discernible domains of SecA which is accompanied by a shielding of hydrophobic surface from solvent. |
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