Nuclear magnetic resonance technology for biological complex systems: Opportunities and challenges

Abstract

Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool in learning the structure, dynamics and interaction of biological macromolecules. In virtue of its rapid development and wide applications, NMR has become an indispensable tool in numerous research fields, which in further benefits from the improvement of NMR spectrometers based on higher sensitivity and resolution, as well as the continuous innovation of NMR experiment methods. Nowadays life science researches are not limited to the traditional questions and technologies. Multidisciplinary studies of life science, physics, chemistry and materials science become new trends. Therefore, new tools are required to study the structure and function of macromolecules in its native or mimic environments, where NMR provides a powerful and versatile weapon. Membrane protein mediates signal transduction, molecular transport and energy metabolism in cells. Hence, the therapeutic potential based on understanding the properties of membrane protein requires extensive investigation to characterize its structure and dynamics. Structural study of membrane protein presents challenging due to its low ability to form protein crystal in a mimetic membrane environment. However, NMR is a suitable tool and plays an important role in studying membrane protein, because it provides possibilities to determine the structure of membrane proteins in an environment similar to its native state. Specifically, optimal membrane mimetic including detergent micelles, bicelles and nanodiscs need to be considered in the structural study of membrane proteins, due to the size limits in solution-state NMR. On the other hand, solid-state NMR (ssNMR) has long been considered as another major method in the field of structural biology because it dominates in studying membrane proteins in native-like lipids. Moreover, oriented sample (OS) ssNMR can be applied to determine the secondary structure, orientation and topology of membrane protein in lipid bilayers, in which the sample should be uniformly aligned in the magnetic field. Recently, basing on the methodological and technological developments in the field of dynamic nuclear polarization (DNP) and proton detection, magic angle spinning (MAS) ssNMR has presented as a promising tool in completely characterization of the structure and dynamics of membrane proteins. Exploring the structure, interaction and function of biomolecules in native environment requires understanding their mechanisms thoroughly in physiologically relevant. In-cell NMR is a branch of high-resolution biomolecular NMR spectroscopy, which brings atomic-resolution insights into the states of macromolecule in native cells. To date, in-cell NMR has been successfully applied to the investigation of bacterial and eukaryotic cells, accordingly, relevant structural and functional information has been obtained. Here we give a general discourse on the existing in-cell NMR approaches and its applications in protein structure determination, interaction and stability. Bone is one of the most intricate natural materials, featuring by its highly hierarchical architecture. Nevertheless, its characteristic organic-inorganic organization presents challenging for most of conventionally analytical and biophysical techniques. Over the past several years, ssNMR has been extensively applied to materials science, enabling insights into the structure and dynamics of complicated biomaterials in atomic-scale. Particularly, ssNMR highlights its unique potential in the research of bone. Specifically, the organic matrix of bone can be explored using 13C-labeled NMR methods, while the inorganic bone mineral can be labeled by 43Ca and 31P. Furthermore, the structural arrangement of the interface between organic matrix and inorganic mineral of bone can be probed using the method of 13C {31P} rotational echo double resonance (REDOR). The abundant structural information in atomic-scale derived from ssNMR has immensely contributed to the establishment of current structural model of bone, hence, aids understanding the molecular mechanisms of bone maturation and diseases.