The effect of aspirin on the interaction of histone 05 and 05-DNA

The linker histones (H1 or H5) which play a key role in the folding of chromatin, are general repressors of gene expression. Nuclei of the mature chicken erythrocytes (and in some mammalian cells) contain both of them. Although the interaction of H5 with DNA is stronger than that of H1, it does not prevent the transcription of some erythroid-specific genes. It has been shown that some modifications have important role in modulating the interactions of histones with DNA, specially regulating the transcription. Histone acetylation changes the chromatin structure into an active form. It has been suggested that aspirin (ASA) acts as an acetylator of proteins. Also, it has been used as an anti-cancer drug in recent years. In this research study, histone H5 was extracted from chicken erythrocytes using a modified method. Purity of the obtained H5 was detected by SDS-P AGE electrophoresis. Spectrophotometric results showed that ASA optimum concentration for H5 acetylation was 6.5 mM after incubation for 210 min at 27 °C. These results are compatible with our previous results for H1 acetylation using both ASA and acetic anhydride (as a standard acetylator). Also, the fluorometric data showed the quenching of H5 emission due to its acetylation and partial unfolding. The acetylated protein had lower electrophoretic mobility on SDS-PAGE due to the increase of its molecular weight after acetylation. The interaction of acetylated histone H5 with DNA decreased about 15 bpDNA/H5 molar ratios at 50% precipitation in comparison with the normal H5. However, after the addition of ASA to the H5-DNA complex, only about 5 bpDNA/ H5 at 50% precipitation was seen. It can be concluded that histone H5 (like H1) is acetylated by aspirin. Acetylation neutralizes H5 positive charges, modifies its conformation, and reduces its interaction with DNA.