Wilhelm bernhard workshop on the cell nucleus

THE NON-HISTONE CHROMOSOMAL PROTEIN HMGB1 AS A MODULATOR OF CHROMATIN STRUCTURE

Polyanichko A., Chikhirzhina E., Skvortsov A., Kostyleva E., Vorob’ev V.

Institute of Cytology of the Russian Academy of Sciences, St.-Petersburg, Russia
The structure and function of the non-histone chromosomal protein HMGB1 as a modulator of chromatin structure have been studied. Interaction of the protein HMGB1 with DNA has been investigated using hydrodynamic and optical methods including complementary methods of circular dichroism and absorption spectroscopy in UV and IR regions. The role of different domains of the HMGB1 molecule in interaction with DNA has been analyzed by comparison of the full-length native HMGB1 molecule and the recombinant HMGB1-(A+B) molecule with a deleted negatively charged C-terminal domain of the HMGB1 molecule. It was shown that interaction of the HMGB1 with DNA proceeds in two stages. In the first stage, at the low protein/DNA ratios, interaction of the HMGB1 is defined mainly by the activity of the DNA binding domain, this interaction being slightly weakened by the influence of the acidic C-terminal domain of HMGB1. Interaction of the HMGB1 with DNA results in changes in the conformation of the components of the complex. The alpha-helicity of the DNA binding domains increases in HMGB1 and local structural changes in DNA occur which induce the DNA condensation. At the rise of the protein/DNA ratio and with the increase of ionic strength the cooperative phase in HMGB1-DNA interaction begins which is connected with protein-protein interactions between the HMGB1 molecules. The unordered negatively charged C-terminal tail of the HMGB1 plays an essential role in the formation of the complexes. Recombinant protein HMGB1-(A+B) lacking the C-terminal domain forms with DNA the complexes with a highly ordered structure, which reveal anomalously high optical activity. The data obtained show that the negatively charged C-terminal domain of the HMGB1 can perform in chromatin the function of modulator of the both protein-protein and protein-DNA interactions.