Depending on the degree of methylation, the mono-, di-, and tri-methylated lysine structures are formed with different biochemical and functional consequences. The positively charged tri-methylated lysine presents the same motif R-N(CH 3 ) + 3 as the choline headgroup, and these methylation patterns modulate the interactions between histone proteins and DNA and constitute the core mechanisms of epigenetics. Given the ubiquity of the TMA motif-especially with choline groups decorating the surface of virtually all membranes-it is important to understand the molecular details Figure : Chemical structures of choline as the head group of phosphatidylcholine and trimethyllysine, with their cationic tetramethylammonium (TMA) motif; hyaluronic acid dimer with the carboxylate groups (gray arrows) and the acetate (Ac) molecular anionic species.