Determination of the structure of symmetric coiled-coil proteins from NMR data: application of the leucine zipper proteins Jun and GCN4.

Previous attempts to determine the solution structures of homodimeric 'leucine zippers' using nuclear magnetic resonance (NMR) spectroscopy have been impeded by the complete symmetry of these coiled-coil molecules, which makes it impossible a priori to distinguish between intra- and intermonomer dipolar connectivities. Consequently, a number of ad hoc approaches have been used in an attempt to derive tertiary solution structures of these molecules from the NMR data. In this paper we present a more rigorous approach for analysing the NMR spectra of symmetric coiled-coil proteins. This analysis is based on calculations of intra- and intermonomer interproton distances in the recently determined crystal structure of the GCN4 leucine zipper [O'Shea, E.K., Klemm, J.D., Kim, P.S. and Alber, T. (1991) Science, 254, 539-543] and in symmetric coiled-coil models of the leucine zippers of GCN4 and the human oncoprotein Jun which we constructed using a dynamic simulated annealing approach. This analysis has enabled the formulation of a set of rules for interpreting the NMR spectra of symmetric coiled-coil proteins and has also led to the prediction of novel dipolar connectivities which we demonstrate in a 2-D NMR spectrum of the homodimeric Jun leucine zipper.