In-Cell Protein NMR Spectroscopy

Structural biology in general, including NMR, is highly reductionist-simplifying complex systems to their component parts, and extrapolating to the native interactions that occur in cells and tissues. The strengths of NMR analysis-high-resolution structure determination, intermolecular interface identification, dynamic molecular descriptions, site-specific electronic characterization-are patently applicable to cells and tissues, but face a number of technical complexities, including sensitivity, selectivity, and localization. Additionally, while there is adequate understanding of crowding and similar physicochemical effects in homogeneous polymer systems, the heterogeneity of the cellular environment adds an additional challenge (or opportunity) for potentially new phenomena to be observed. Current literature describes a number of approaches delving into the great complexity of in-cell NMR while maintaining the advantages of high-resolution NMR spectroscopy. The related literature has been reviewed recently [1-8]. In this chapter, we summarize protocols and potential applications rather than present a historical review of prior work. Protocols are identified or outlined to provide (i) in-cell determination of conformation, (ii) a comparison of perturbations of structure between in-cell and in vitro environments, (iii) mapping of in-cell protein-protein interactions, (iv) other protein-ligand interaction analyses, (v) post-translational modifications, and (vi) studies of nucleic acids.