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Isotope-Aided Methods for Biological NMR Spectroscopy: Past, Present, and Future

ABSTRACT: This chapter starts by providing a historical background of our research endeavors over the past half-century to develop various isotope-aided methods in biological NMR spectroscopy, since innovations bloom only on the rich ground cultivated by previous investigators. We then focused on the stereo-array isotope-labeling (SAIL) method, one of our recent accomplishments, which culminates the isotope-aided NMR technologies for structural studies of proteins from various aspects: accurate structural determinations of large proteins, elaboration for automated structural determination, highly efficient and versatile residue-selective methyl labeling with newly developed auxotrophic E. coli strains, large-amplitude slow-breathing motion (LASBM) as revealed by the aromatic ring flipping of the residues in ligand-binding interfaces, and applications of the deuterium-induced 13C-NMR isotope shift to investigate the hydrogen exchange phenomena of side-chain polar groups. Meanwhile, the expected role of NMR spectroscopy has been rapidly shifting from structure determinations to dynamics studies of biologically interesting targets, such as membrane proteins and larger protein complexes. The dynamic aspects of protein–protein and protein–ligand interactions are closely related to their biological functions and can be efficiently studied by using proteins residue selectively labeled with amino acids bearing optimized labeling patterns, prepared by cellular expression. We are absolutely confident that biological NMR spectroscopy will continually develop with further innovations of isotope-labeling technologies in the coming era, featuring ultrahigh field spectrometers beyond 1 GHz.

SUBMITTER: The Nuclear Magnetic Resonance Society of Japan

PROVIDER: S-EPMC7122432 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Project description:In this perspective, we describe our efforts to innovate the current isotope-aided NMR methodology to investigate biologically important large proteins and protein complexes, for which only limited structural information could be obtained by conventional NMR approaches. At the present time, it is widely believed that only backbone amide and methyl signals are amenable for investigating such difficult targets. Therefore, our primary mission is to disseminate our novel knowledge within the biological NMR community; specifically, that any type of NMR signals other than methyl and amide groups can be obtained, even for quite large proteins, by optimizing the transverse relaxation properties by isotope labeling methods. The idea of "TROSY by isotope labeling" has been cultivated through our endeavors aiming to improve the original stereo-array isotope labeling (SAIL) method (Kainosho et al., Nature 440:52-57, 2006). The SAIL TROSY methods subsequently culminated in the successful observations of individual NMR signals for the side-chain aliphatic and aromatic 13CH groups in large proteins, as exemplified by the 82 kDa single domain protein, malate synthase G. Meanwhile, the expected role of NMR spectroscopy in the emerging integrative structural biology has been rapidly shifting, from structure determination to the acquisition of biologically relevant structural dynamics, which are poorly accessible by X-ray crystallography or cryo-electron microscopy. Therefore, the newly accessible NMR probes, in addition to the methyl and amide signals, will open up a new horizon for investigating difficult protein targets, such as membrane proteins and supramolecular complexes, by NMR spectroscopy. We briefly introduce our latest results, showing that the protons attached to 12C-atoms give profoundly narrow 1H-NMR signals even for large proteins, by isolating them from the other protons using the selective deuteration. The direct 1H observation methods exhibit the highest sensitivities, as compared to heteronuclear multidimensional spectroscopy, in which the 1H-signals are acquired via the spin-coupled 13C- and/or 15N-nuclei. Although the selective deuteration method was launched a half century ago, as the first milestone in the following prosperous history of isotope-aided NMR methods, our results strongly imply that the low-dimensional 1H-direct observation NMR methods should be revitalized in the coming era, featuring ultrahigh-field spectrometers beyond 1 GHz.

Project description:Hsp70 molecular chaperones play central roles in maintaining a healthy cellular proteome. Hsp70s function by binding to short peptide sequences in incompletely folded client proteins, thus preventing them from misfolding and/or aggregating, and in many cases holding them in a state that is competent for subsequent processes like translocation across membranes. There is considerable interest in predicting the sites where Hsp70s may bind their clients, as the ability to do so sheds light on the cellular functions of the chaperone. In addition, the capacity of the Hsp70 chaperone family to bind to a broad array of clients and to identify accessible sequences that enable discrimination of those that are folded from those that are not fully folded, which is essential to their cellular roles, is a fascinating puzzle in molecular recognition. In this article we discuss efforts to harness computational modeling with input from experimental data to develop a predictive understanding of the promiscuous yet selective binding of Hsp70 molecular chaperones to accessible sequences within their client proteins. We trace how an increasing understanding of the complexities of Hsp70-client interactions has led computational modeling to new underlying assumptions and design features. We describe the trend from purely data-driven analysis toward increased reliance on physics-based modeling that deeply integrates structural information and sequence-based functional data with physics-based binding energies. Notably, new experimental insights are adding to our understanding of the molecular origins of "selective promiscuity" in substrate binding by Hsp70 chaperones and challenging the underlying assumptions and design used in earlier predictive models. Taking the new experimental findings together with exciting progress in computational modeling of protein structures leads us to foresee a bright future for a predictive understanding of selective-yet-promiscuous binding exploited by Hsp70 molecular chaperones; the resulting new insights will also apply to substrate binding by other chaperones and by signaling proteins.

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Isotope-Aided Methods for Biological NMR Spectroscopy: Past, Present, and Future

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