Abstract
The thermal stability of the core histone dimer H2A-H2B has been studied by high-sensitivity differential scanning calorimetry and circular dichroism spectroscopy. The unfolding transition temperature of the 28 kDa H2A-H2B dimer increases as a function of both the ionic strength of the solvent and the total protein concentration. At neutral pH and physiological ionic strength, the thermal denaturation is centered at about 50°C with a corresponding enthalpy change of about 40 kcal/mol of 14 kDa monomer unit and an excess heat capacity of about 1.4 kcal/(K·mol) of 14 kDa monomer unit. The H2A-H2B dimer is stable mainly between pH 5.5 and 10.5. Below pH 4.0, the system is unfolded at all temperatures. The thermodynamic analysis is performed at low ionic strength where almost complete reversibility is attained, since higher salt conditions seem to promote aggregation and irreversibility of the transitions. Analysis of the data shows that at low ionic strength and pH values between 6.5 and 8.5, the H2A-H2B dimer behaves as a highly cooperative system, melting as a single unit without any detectable intermediates of dissociated, yet folded, H2A and H2B monomers. This is consistent with the observed protein concentration dependence of the midpoint of the thermal denaturation. The two-state unfolding process can be described by the general scheme AB → 2U, indicating that the individual H2A and H2B polypeptides are folded, stable entities only when complexed as the H2A-H2B dimer and that the major contribution to the stabilization of the dimer derives from the coupling between the H2A and H2B interfaces.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 5988-5996 |
| Number of pages | 9 |
| Journal | Biochemistry® |
| Volume | 34 |
| Issue number | 17 |
| State | Published - 1995 |
Fingerprint
ASJC Scopus subject areas
- Biochemistry
Cite this
Thermodynamic studies of the core histones : Ionic strength and pH dependence of H2A-H2B dimer stability. / Karantza, Vassiliki; Freire, Ernesto I; Freire, Ernesto; Moudrianakis, Evangelos N.
In: Biochemistry®, Vol. 34, No. 17, 1995, p. 5988-5996.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Thermodynamic studies of the core histones
T2 - Ionic strength and pH dependence of H2A-H2B dimer stability
AU - Karantza, Vassiliki
AU - Freire, Ernesto I
AU - Freire, Ernesto
AU - Moudrianakis, Evangelos N.
PY - 1995
Y1 - 1995
N2 - The thermal stability of the core histone dimer H2A-H2B has been studied by high-sensitivity differential scanning calorimetry and circular dichroism spectroscopy. The unfolding transition temperature of the 28 kDa H2A-H2B dimer increases as a function of both the ionic strength of the solvent and the total protein concentration. At neutral pH and physiological ionic strength, the thermal denaturation is centered at about 50°C with a corresponding enthalpy change of about 40 kcal/mol of 14 kDa monomer unit and an excess heat capacity of about 1.4 kcal/(K·mol) of 14 kDa monomer unit. The H2A-H2B dimer is stable mainly between pH 5.5 and 10.5. Below pH 4.0, the system is unfolded at all temperatures. The thermodynamic analysis is performed at low ionic strength where almost complete reversibility is attained, since higher salt conditions seem to promote aggregation and irreversibility of the transitions. Analysis of the data shows that at low ionic strength and pH values between 6.5 and 8.5, the H2A-H2B dimer behaves as a highly cooperative system, melting as a single unit without any detectable intermediates of dissociated, yet folded, H2A and H2B monomers. This is consistent with the observed protein concentration dependence of the midpoint of the thermal denaturation. The two-state unfolding process can be described by the general scheme AB → 2U, indicating that the individual H2A and H2B polypeptides are folded, stable entities only when complexed as the H2A-H2B dimer and that the major contribution to the stabilization of the dimer derives from the coupling between the H2A and H2B interfaces.
AB - The thermal stability of the core histone dimer H2A-H2B has been studied by high-sensitivity differential scanning calorimetry and circular dichroism spectroscopy. The unfolding transition temperature of the 28 kDa H2A-H2B dimer increases as a function of both the ionic strength of the solvent and the total protein concentration. At neutral pH and physiological ionic strength, the thermal denaturation is centered at about 50°C with a corresponding enthalpy change of about 40 kcal/mol of 14 kDa monomer unit and an excess heat capacity of about 1.4 kcal/(K·mol) of 14 kDa monomer unit. The H2A-H2B dimer is stable mainly between pH 5.5 and 10.5. Below pH 4.0, the system is unfolded at all temperatures. The thermodynamic analysis is performed at low ionic strength where almost complete reversibility is attained, since higher salt conditions seem to promote aggregation and irreversibility of the transitions. Analysis of the data shows that at low ionic strength and pH values between 6.5 and 8.5, the H2A-H2B dimer behaves as a highly cooperative system, melting as a single unit without any detectable intermediates of dissociated, yet folded, H2A and H2B monomers. This is consistent with the observed protein concentration dependence of the midpoint of the thermal denaturation. The two-state unfolding process can be described by the general scheme AB → 2U, indicating that the individual H2A and H2B polypeptides are folded, stable entities only when complexed as the H2A-H2B dimer and that the major contribution to the stabilization of the dimer derives from the coupling between the H2A and H2B interfaces.
UR - http://www.scopus.com/inward/record.url?scp=0029053420&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0029053420&partnerID=8YFLogxK
M3 - Article
C2 - 7727455
AN - SCOPUS:0029053420
VL - 34
SP - 5988
EP - 5996
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 17
ER -