Hydrophobic side-chain size is a determinant of the three-dimensional structure of the p53 oligomerization domain

The p53 tumor suppressor oligomerization domain, a dimer of two primary dimers, is an independently folding domain whose subunits consist of a beta-strand, a tig ht turn anti an alpha-helix. To evaluate the effect of hydrophobic side-chains on three-dimensional structure, we substituted residues Phe341 and Leu344 in the a-helix with other hydrophobic amino acids. Substitutions that resulted in residue 341 having a smaller side-chain than residue 344 snitched the stoichiometry of the domain front tetrameric to dimeric, The three-dimensional structure of one such dimer was determined by multidimensional NMR spectroscopy, When compared with the primary dimer of the wild-type p53 oligomerization domain, the mutant dimer showed a snitch in alpha-helical packing from anti-parallel to parallel and rotation of the alpha-helices relative to the beta-strands, Hydrophobic side-chain size is therefore an important determinant of a protein fold.