The solution structure of the leucine zipper motif of the Jun oncoprotein homodimer

Proton NMR studies have been performed on a 9.8-kDa synthetic fragment comprising the homodimeric leucine zipper domain of the human oncoprotein Jun to ascertain its conformation in aqueous solution. Analysis of two-dimensional scalar and dipolar-coupling experiments enabled almost all proton resonances to be sequence-specifically assigned and further revealed that the Jun leucine zipper forms a completely symmetric dimer in solution, consistent with the formation of a coiled-coil arrangement of parallel alpha-helical strands. The rates of exchange of individual amide protons with solvent, as well as hydrogen-bond lengths predicted from amide proton chemical shifts, are shown to correlate with residue position in the coiled-coil. A subset of 209 unambiguous distance constraints was compiled using rules recently formulated for interpreting the NOESY spectra of symmetric coiled-coils, and these were used in combination with experimentally determined hydrogen bond and dihedral angle constraints to compute a solution structure for the Jun leucine zipper domain.