Binding the mammalian high mobility group protein AT-hook 2 to AT-rich deoxyoligonucleotides: enthalpy-entropy compensation

Biophys J. 2009 May 20;96(10):4144-52. doi: 10.1016/j.bpj.2009.02.015.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • AT Rich Sequence*
  • Animals
  • Base Sequence
  • Buffers
  • Calorimetry, Differential Scanning
  • DNA / genetics
  • DNA / metabolism
  • Deoxyribonucleotides / genetics*
  • Deoxyribonucleotides / metabolism*
  • Entropy*
  • HMGA2 Protein / metabolism*
  • Inverted Repeat Sequences
  • Nucleic Acid Denaturation
  • Protein Binding / drug effects
  • Sodium Chloride / pharmacology
  • Solutions
  • Titrimetry
  • Transition Temperature


  • Buffers
  • Deoxyribonucleotides
  • HMGA2 Protein
  • Solutions
  • Sodium Chloride
  • DNA