Rapid global structure determination of large RNA and RNA complexes using NMR and small-angle X-ray scattering.

Among the greatest advances in biology today are the discoveries of various roles played by RNA in biological processes. However, despite significant advances in RNA structure determination using X-ray crystallography [1] and solution NMR [2-4], the number of bona fide RNA structures is very limited, in comparison with the growing number of known functional RNAs. This is because of great difficulty in growing crystals or/and obtaining phase information, and severe size constraints on structure determination by solution NMR spectroscopy. Clearly, there is an acute need for new methodologies for RNA structure determination. The prevailing approach for structure determination of RNA in solution is a "bottom-up" approach that was basically transplanted from the approach used for determining protein structures, despite vast differences in both structural features and chemical compositions between these two types of biomacromolecules. In this chapter, we describe a new method, which has been reported recently, for rapid global structure determination of RNAs using solution-based NMR spectroscopy and small-angle X-ray scattering. The method treats duplexes as major building blocks of RNA structures. By determining the global orientations of the duplexes and the overall shape, the global structure of an RNA can be constructed and further regularized using Xplor-NIH. The utility of the method was demonstrated in global structure determination of two RNAs, a 71-nt and 102-nt RNAs with an estimated backbone RMSD ∼3.0Å. The global structure opens door to high-resolution structure determination in solution.