Histone subunit interactions as investigated by high pressure.

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Histones are crucial for DNA packaging in chromatin.
• Understanding histone subunit interactions is key to comprehending chromatin structure and function.
• Previous studies indicated histone tetramers can form dimers of tetramers.

Purpose of the Study:

• To investigate the subunit interactions of histone H2A-H2B dimers and H3/H4 tetramers.
• To determine the dissociation constants (Kd) of these histone complexes.
• To explore the effect of pressure and salt concentration on histone complex stability.

Main Methods:

• High-pressure fluorescence polarization.
• Labeling histone proteins with 5-(dimethylamino)-naphthalene-1-sulfonate (dansyl).
• Measuring fluorescence polarization as a function of pressure.

Main Results:

• The dissociation constant for the chicken erythrocyte (CE) H2A-H2B dimer was approximately 1 x 10(-7) M at 2.0 M NaCl, stabilizing to 6 x 10(-8) M at 200 mM NaCl.
• The calf thymus (CT) H3/H4 octamer to dimer transition had a dissociation constant of 1 x 10(-21) M3 at 2 M NaCl, decreasing stability to 9 x 10(-21) M3 at 200 mM NaCl.
• A small negative volume change was observed for the dissociation of the core particle octamer.

Conclusions:

• High-pressure fluorescence polarization is effective for studying histone complex dynamics.
• Salt concentration significantly impacts the stability of histone H2A-H2B dimers and H3/H4 tetramers.
• The findings provide insights into the structural transitions of core histone complexes.