NMR STRUCTURAL CHARACTERIZATION OF THE CDK INHIBITOR P19(INK4D)

p19(INK4d) is a 165 amino acid protein that belongs to the INK4 family of CDK4 and CDK6 inhibitors, Assignments of H-1,N-15 and C-13 resonan ces have enabled the determination of the secondary structure of the p rotein which is largely alpha-helical (residues 14-18, 21-29, 54-62, 7 7-83, 87-95, 110-116, 120-128, 142-148 and 152-160), The protein compr ises five 32-amino acid ankyrin-like repeats; each ankyrin repeat cont ains a helix-beta-turn-helix core, The exception is the second ankyrin repeat, which lacks the first helix, All beta-turns have a central gl ycine residue Banked by two residues in beta-conformations, There is a lso a high conservation of Ala at position 8 in the first helix and Le u-Leu(Val) at positions 17-18 of the second helix in all ankyrin repea ts of p19, The location of the helix-turn-helix segments found in p19 should be general for all other members of the INK4 family, including, for example, a homologous tumor suppressor p16(INK4a). H-1-N-15 heter onuclear steady-state NOE measurements on p19 indicate that most of th e backbone of p19(INK4d) exists in a well defined structure of limited conformational flexibility on the nano- to picosecond time scale.