Calorimetric studies of the energetics of protein-DNA interactions in the E. coli methionine repressor (MetJ) system.
Calorimetric measurements of binding of a specific DNA fragment and S-adenosyl methionine (SAM) co-repressor molecules to the E. coli methionine repressor (MetJ) show significant differences in the energetics of binary and ternary protein-DNA complexes. Formation of the MetJ:SAM:DNA ternary complex is significantly more exothermic (delta H congruent to -99 kJ.mol-1) than either MetJ:DNA or MetJ:SAM binary complexes alone (delta H congruent to -10 kJ.mol-1 each). The protein is also significantly more stable to unfolding (delta Tm congruent to 5.4 degrees C) when bound to DNA. These observations suggest that binding of SAM to the protein-DNA complex leads to a significant reduction in dynamic flexibility of the ternary complex, with considerable entropy-enthalpy compensation, not necessarily involving any overall conformational change.
Cooper
A
A
Department of Chemistry, Glasgow University, Scotland, UK.
McAlpine
A
A
Stockley
P G
PG
D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D002151:Calorimetry; D004269:DNA, Bacterial / Q000138:chemical synthesis / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism; D013816:Thermodynamics
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; C060486:methionine repressor protein, Bacteria; C489220:methionine repressor protein, E coli; D012436:S-Adenosylmethionine