Entropic nature of the interaction between promoter bound CRP mutants and RNA polymerase.
Biochemistry 2003;
42:1958-68. [PMID:
12590582 DOI:
10.1021/bi026755v]
[Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The interaction between CRP, T127L, S128A, and CRP and RNA polymerase bound to a 104 bp synthetic promoter were determined by ITC at 298 K and ranges from a deltaG(b) degrees = 1.4 +/- 0.8 kJ mol(-)(1) (cAMP-ligated S128A) to 4.5 +/- 0.3 kJ mol(-)(1) (cAMP-ligated double mutant CRP) with endothermicities that range from 4 +/- 3 kJ mol(-)(1) (cAMP-ligated CRP) to 47 +/- 8 kJ mol(-)(1) (cGMP-ligated T127L). The interaction is, thus, entropically driven, exhibits enthalpy-entropy compensation, and increases the binding affinity of the RNA polymerase to the promoter by factors ranging from 1.7 +/- 0.1 (cAMP-ligated S128A) to 6.1 +/- 0.1 (cAMP-ligated CRP). Although the binding affinities to the promoter alone, except for cAMP-ligated S128A, are the same as to a shorter 40 bp duplex containing the same CRP consensus binding site sequence (conDNA), the binding enthalpies of CRP/mutant to the promoter are lower by factors of 2-3 x than the corresponding binding enthalpies to conDNA. Small angle neutron scattering measurements on the DNA-CRP/mutant complexes in D(2)O/H(2)O solutions exhibit an increase in the Rg of the CRP/mutant component from 22 to 27-31 A that can be attributed to a conformational change in the N-terminal domain of CRP. The Rg = 27 A for the bound conDNA can be attributed to a slight unwinding of the DNA in solution that would also enhance the activation of transcription. The Rg = 53 +/- 3 A for the bound promoter is attributed to bending of the promoter in solution that can be responsible for the lower CRP/mutant-promoter binding endothermicities.
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