Selective molecular recognition of methylated lysines and arginines by cucurbit[6]uril and cucurbit[7]uril in aqueous solution

摘要

Cucurbit[7]uril selectively binds the epigenetic mark N~e,N~e,N~e-trimethyllysine (LysMe_3, K_(CB[7]) (1.8 +- 0.6)x 10~6 dm~3 mor~1) by 3500-fold over lysine ((5.3 +- 0.7) x 10~2 dm~3 mol~(-1)) in aqueous solution, using ion-dipole interactions and the hydrophobic effect, rather than cation-π interactions, as in the "aromatic cages" of p-SC_3-calix[4]arene hosts or chromodomain proteins which recognize LysMe_3. The trend in K_(cb[7]) of LysMe_3 > LysMe_2 > LysMe > Lys follows the recognition pattern of the chromodomain HP1 and other LysMe_n protein readers. With CB[6], protonation of the guest carboxyIate group is required for the formation of inclusion complexes with the LysMe_n series. The CB[7] host also displays modest selectivity between the asymmetric ((2.0 +- 0.3) × 10~3 dm~3 mol~(-1)) and symmetric ((6.1 +- 0.6) x 10~3 dm~3 mol~(-1)) dimethylarginines, both of which bind more strongly than the parent arginine or monomethylarginine.