Binding the mammalian high mobility group protein AT-hook 2 to AT-rich deoxyoligonucleotides: enthalpy-entropy compensation.
HMGA2 is a DNA minor-groove binding protein. We previously demonstrated that HMGA2 binds to AT-rich DNA with very high binding affinity where the binding of HMGA2 to poly(dA-dT)(2) is enthalpy-driven and to poly(dA)poly(dT) is entropy-driven. This is a typical example of enthalpy-entropy compensation. To further study enthalpy-entropy compensation of HMGA2, we used isothermal-titration-calorimetry to examine the interactions of HMGA2 with two AT-rich DNA hairpins: 5'-CCAAAAAAAAAAAAAAAGCCCCCGCTTTTTTTTTTTTTTTGG-3' (FL-AT-1) and 5'-CCATATATATATATATAGCCCCCGCTATATATATATATATGG-3' (FL-AT-2). Surprisingly, we observed an atypical isothermal-titration-calorimetry-binding curve at low-salt aqueous solutions whereby the apparent binding-enthalpy decreased dramatically as the titration approached the end. This unusual behavior can be attributed to the DNA-annealing coupled to the ligand DNA-binding and is eliminated by increasing the salt concentration to approximately 200 mM. At this condition, HMGA2 binding to FL-AT-1 is entropy-driven and to FL-AT-2 is enthalpy-driven. Interestingly, the DNA-binding free energies for HMGA2 binding to both hairpins are almost temperature independent; however, the enthalpy-entropy changes are dependent on temperature, which is another aspect of enthalpy-entropy compensation. The heat capacity change for HMGA2 binding to FL-AT-1 and FL-AT-2 are almost identical, indicating that the solvent displacement and charge-charge interaction in the coupled folding/binding processes for both binding reactions are similar.
Joynt
Suzanne
S
Department of Chemistry & Biochemistry, Florida International University, Miami, Florida 33199, USA.
Morillo
Victor
V
Leng
Fenfei
F
D020856:AT Rich Sequence; D000818:Animals; D001483:Base Sequence; D002021:Buffers; D002152:Calorimetry, Differential Scanning; D004247:DNA / Q000235:genetics / Q000378:metabolism; D003854:Deoxyribonucleotides / Q000235:genetics* / Q000378:metabolism*; D019277:Entropy; D025743:HMGA2 Protein / Q000378:metabolism*; D055029:Inverted Repeat Sequences; D009691:Nucleic Acid Denaturation; D011485:Protein Binding / Q000187:drug effects; D012965:Sodium Chloride / Q000494:pharmacology; D012996:Solutions; D017186:Titrimetry; D044366:Transition Temperature
D002021:Buffers; D003854:Deoxyribonucleotides; D025743:HMGA2 Protein; D012996:Solutions; D012965:Sodium Chloride; D004247:DNA