Dynamics Simulation on the Flexibility and Backbone Motions of HP1 Chromodomain Bound to Free and Lysine 9-Methylated Histone H3 Tails

摘要

Histone methylation has emerged as a central epigenetic modification with both activating and repressive roles in eukaryotic chromatin. Drosophila HP1 (heterochromatin-associated protein 1) is one of the chromodomain proteins that contain the essential aromatic residues as the recognition pocket for lysine methylated histone H3 tail. The aromatic cage indicates that the complex of chromodomain protein binding lysine methylated histone H3 tail can be seen as a typical host-guest system between protein and protein. About 10-ns molecular dynamics simulations have been carried out in this study to examine how the presence of mono-, trimethylated lysine 9 histone H3 tail (Me1K9, Me3K9 H3) influences the motions of HP1 protein receptor. The study shows that the conformation of HP1 protein free of H3 tail easily changes, whereas that of HP1 protein bound to methylated H3 tail does not. But the conformation of inserted Me1K9 H3 changes obviously as the Me1K recognition makes hydrogen-bonded interactions associated with the aromatic cage even more unstable than those in free HIII protein. The conformational change of Me1K9 H3 is correlated with the motions of HP1 protein. As the recognition factor going from Me1K to Me3K produces a more favorable interaction for aromatic ring, hydrogen-bonded interactions associated with aromatic cage in Me3K9 H3-HP1 complex were observed to be much more stable than those in Me1K9 H3-HP1 complex and free HP1. Because of correlation, the flexibility of Me3K9 H3 decreases. The simulations indicate that both the MeK and the surrounding histone tail sequence are necessary features of recognition which significantly affect the flexibility and backbone motions of HP1 chromodomain. These findings confirm a regulatory mechanism of protein-protein interactions through a trimethylated post-translational modification. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 1135-1147, 2009