NMR spin state exchange spectroscopy reveals equilibrium of two distinct conformations of leucine zipper GCN4 in solution.

The resonance assignment, secondary structure, and dynamic properties of a stable noncoiled coil conformation of the dimerization domain from yeast transcription activation factor GCN4 (Leu zipper; LZGCN4) are presented. Introduced in this paper, a new line of fully optimized spin state exchange experiments, XYEX-TROSY, applied to 1HN, 15N and 1Halpha,13Calpha moieties, established that in broad range of pH and buffer conditions the classical LZGCN4 coiled coil dimer is in a dynamic equilibrium with another distinct conformation (denoted here as x-form) and enabled complete assignment of the resonances stemming from the x-form. The LZGCN4 x-form is generally less structured in comparison with the classical GCN4-p1 coiled coil, but still retains a structured alpha-helical central core. The implications for folding properties and biological significance are discussed.