Determination of the Solution Structure of Isolated Histone H2A-H2B Heterodimer by using CS-Rosetta

CS-Rosetta is a program for protein structure determination from NMR experimental parameters and is able to determine solution structures of proteins only from the chemical shift values. However, to determine structures only from the chemical shift values, the target protein have to be a monomer, less than about 120 residues, and smaller flexible region. Histone H2A-H2B heterodimer, which is contained in histone octamer, is out of this limitation. In the present study, we applied CS-Rosetta to determine the solution structure of isolated histone H2A-H2B heterodimer only from chemical shift values. As the results, our solution structures are in good agreement with the chemical shifts values and the chemical shift indices observed from the NMR experiments. In the solution structures, H2A and H2B each contain a histone fold, comprising four α-helices and two β-strands, together with the long disordered N- and C-terminal H2A tails and the long N-terminal H2B tail. The N-terminal αN helix, C-terminal β3 strand, and 310 helix of H2A observed in the H2A-H2B nucleosome structure are disordered in isolated H2A-H2B. In addition, the H2A α1 and H2B αC helices are not well fixed in the heterodimer, and the H2A and H2B tails are not completely random coils, which are consistent with the results of NMR experiments.