A method for systematic mapping of protein lysine methylation identifies functions for HP1ß in DNA damage response.

Lysine methylation occurs on both histone and nonhistone proteins. However, our knowledge on the prevalence and function of nonhistone protein methylation is poor. We describe an approach that combines peptide array, bioinformatics, and mass spectrometry to systematically identify lysine methylation sites and map methyllysine-driven protein-protein interactions. Using this approach, we identified a high-confidence and high-resolution interactome of the heterochromatin protein 1ß (HP1ß) and uncovered, simultaneously, numerous methyllysine sites on nonhistone proteins. We found that HP1ß binds to DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and regulates its localization to double-strand breaks (DSBs) during DNA damage response (DDR). Mutation of the methylation sites in DNA-PKcs or depletion of HP1ß in cells caused defects in DDR. Furthermore, we showed that the methylation of DNA-PKcs and many other proteins in the HP1ß interactome undergoes large changes in response to DNA damage, indicating that Lys methylation is a highly dynamic posttranslational modification.

A soliton phenomenon in langmuir monolayers of amphiphilic bistable rotaxanes.

Surface pressure-area isotherms, light scattering microscopy, and atomic force microscopy have all been used to provide information about the stabilities and dynamics of Langmuir monolayers composed of amphiphilic bistable [2]rotaxane molecules. Superstructures that have the appearance of localized mobile solitons are formed during the compression of monolayers of the [2]rotaxanes below their collapse pressures. Solitons move solely in a linear trajectory in both directions across the film, perpendicular to the compression direction, without any apparent broadening or change in their shape.