BACKBONE DYNAMICS OF THE CDK INHIBITOR P19(INK4D) STUDIED BY N-15 NMRRELAXATION EXPERIMENTS AT 2 FIELD STRENGTHS

The four members of the INK4 gene family, p16(INK4a), p15(INK4b), p18( INK4c) and p19(INK4d), are known to bind, to and inhibit the closely r elated cyclin-dependent kinases CDK4 and CDK6 as part of the regulatio n of the G1/S transition in the cell division cycle. Loss of INK4 gene product function, and particularly that of p16(INK4a), is found in hu man cancer. N-15 NMR relaxation rates of p19(INK4d) were analyzed usin g the reduced spectral density mapping method. Most of the backbone of p19(INK4d) exists in a well-defined structure of limited conformation al flexibility on the nanosecond to picosecond time-scales. Introducin g appropriate scaling to account for the effects of anisotropy, a cons iderable amount of exchange broadening was found for several residues throughout the sequence, especially residues in the second ankyrin rep eat and in the beginnings and ends of loops connecting ankyrin repeats . A possible mode of binding between p19(INK4d) and CDK4 and CDK6 coul d therefore involve the loop segments of p19(INK4d). The average overa ll correlation time tau(m)(eff) Was determined to be 13.6 ns, reflecti ng the tendency of p19(INK4d) to aggregate. (C) 1998 Academic Press.