BACKBONE DYNAMICS OF THE OLIGOMERIZATION DOMAIN OF P53 DETERMINED FROM N-15 NMR RELAXATION MEASUREMENTS

The backbone dynamics of the tetrameric p53 oligomerization domain (re sidues 319-360) have been investigated by two-dimensional inverse dete cted heteronuclear H-1-N-15 NMR spectroscopy at 500 and 600 MHz. (NT1) -N-15, T-2, and heteronuclear NOEs were measured for 39 of 40 non-prol ine backbone NH vectors at both field strengths. The overall correlati on time for the tetramer, calculated from the T-1/T-2 ratios, was foun d to be 14.8 ns at 35 degrees C. The correlation times and amplitudes of the internal motions were extracted from the relaxation data using the model-free formalism (Lipari G, Szabo A, 1982, J Am Chem Soc 104:4 546-4559). The internal dynamics of the structural core of the p53 oli gomerization domain are uniform and fairly rigid, with residues 327-35 4 exhibiting an average generalized order parameter (S-2) Of 0.88 +/- 0.08. The N- and C-termini exhibit substantial mobility and are unstru ctured in the solution structure of p53. Residues located at the N- an d C-termini, in the beta-sheet, in the turn between the alpha-helix an d beta-sheet, and at the C-terminal end of the alpha-helix display two distinct internal motions that are faster than the overall correlatio n time. Fast internal motions (less than or equal to 20 ps) are within the extreme narrowing limit and are of uniform amplitude. The slower motions (0.6-2.2 ns) are outside the extreme narrowing limit and vary in amplitude. Four residues at the tetramer interface exhibit a small degree of conformational averaging as evidenced by N-15 line broadenin g, possibly due to sliding or rolling of the helices at the interface of the two dimers that form the tetramer.