Thermodynamic studies of the interaction of trp aporepressor with tryptophan analogs.
The association of L-tryptophan and some of its analogs, including three conformationally restricted analogs, with trp aporepressor (apo trpR) was studied by isothermal titration microcalorimetry. Contributions of the functional groups of a ligand to the free energy change, delta G degrees', and enthalpy change, delta H degree', of the interaction were evaluated on a molecular basis. Analogs without the alpha-amino group (i.e. desamino analogs) bind with a slightly higher affinity to the protein. On the other hand, descarboxy analogs show weaker binding to the apo trpR. In addition, it is found that there exists enthalpy-entropy compensation for the association of the congener series of ligands with the protein. The entropy change, delta S degree', appears to play a more important role in the binding of the conformationally restricted analogs than in the binding of L-tryptophan and the unlocked ligands.
Department of Chemistry, University of Mississippi, University 38677.
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D001059:Apoproteins / Q000737:chemistry*; D001426:Bacterial Proteins; D001665:Binding Sites; D002151:Calorimetry; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D008024:Ligands; D008968:Molecular Conformation; D010957:Plasmids; D011485:Protein Binding; D012097:Repressor Proteins / Q000737:chemistry*; D013816:Thermodynamics; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000737:chemistry*
D001059:Apoproteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008024:Ligands; D012097:Repressor Proteins; C027190:TRPR protein, E coli; D014364:Tryptophan