Dear Colleagues,

The emergent properties of living systems derive from the assembly and fluctuation of biomolecules—proteins, nucleic acids, lipids, carbohydrates—in an aqueous environment. For over 50 years, nuclear magnetic resonance (NMR) spectroscopy has been an indispensable tool in biology and its importance in translational research and clinical medicine is growing rapidly. Continual advances in isotopic labeling, instrument performance, and multidimensional NMR methods expand its range of accessibility to molecular systems of ever-increasing size and complexity, including intact cells and tissues. Solution and solid-state NMR are routinely used to solve 3D structures of biomolecular complexes, monitor ligand binding and other types of molecular recognition events, and measure molecular motions across a vast range of timescales. Chemical shifts, coupling constants, relaxation times and other NMR parameters can be combined with data from other biophysical methods and computational modeling to develop realistic descriptions of flexible molecular systems. Translational and clinical applications of NMR include chemical ligand screening for drug discovery, metabolomic analysis of plasma, urine, and cerebrospinal fluid, and FDA-approved diagnostic testing of blood lipoprotein levels. This Special Issue of Molecules illustrates the broad impact on biology and medicine of NMR spectroscopy as a tool to investigate biomolecular structure, recognition and dynamics.

Prof. Dr. Brian F. Volkman
Guest Editor

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• nuclear magnetic resonance
• protein
• DNA
• RNA
• carbohydrate
• lipid
• relaxation
• chemical shift
• stable isotope
• TROSY
• triple-resonance
• non-uniform sampling
• fragment-based screening
• metabolomics

Title: Studying Glycosaminoglycan-Protein Interactions Using NMR Spectroscopy
Authors: Vitor H. Pomin ¹ and Xu Wang ²
Affiliation: 1. Department of Biomolecular Sciences, and Research Institute of Pharmaceutical Sciences, School of Pharmacy, University of Mississippi. (vpomin@olemiss.edu)
2. School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA (xu.wang.4@asu.edu).
Abstract: The formation of intermolecular complexes between glycosaminoglycans (GAGs) and functional proteins is a crucial event in numerous pathophysiological systems. Nuclear Magnetic Resonance (NMR) is one of the most utilized and informative analytical techniques for investigating GAG-protein complexes. Although current NMR techniques such as chemical shift perturbation, saturation transfer difference and transferred nuclear Overhauser effect have revealed valuable information on protein-GAG systems, elucidating high-resolution structures of GAG-protein complexes and studying the dynamics of these often transient interactions continue to be challenging. In addition, obtaining structurally homogeneous and isotopically enriched GAG ligands for structural investigations is also difficult. As a result, understanding of the structure-activity relationship involving GAGs is still primitive. To overcome these deficiencies, several innovative NMR techniques have been developed recently. Here we review some of the latest NMR studies of the physicochemical and biological properties of the various GAG-protein complexes with an emphasize on summarizing the development and utilization of novel NMR techniques that can shed new insights into structure and dynamics of GAG-protein interactions. In particular, we will discuss methods to produce isotopically enriched as well as paramagnetically tagged GAG ligands and novel approaches focused on examining lysine and arginine side chains to identify GAG-binding sites in binding proteins. Results obtained from solid-state NMR will be also presented. Finally, we will discuss the nature of GAG-protein interactions revealed by these studies and their contributions to the understanding of structure-activity relationship of GAGs.

Authors: Fariba Assadi-Porter *, James Radek, Hongyu Rao and Marco Tonelli
Affiliation: Department of Integrative Biology, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA
Email: fariba@nmrfam.wisc.edu
Abstract: Taste signaling is a complex process that is linked to obesity and its associated metabolic syndromes. The sweet taste is mediated through a heterodimeric G protein coupled receptor (GPCR) in a species-specific manner and at multi-tissue specific levels. The sweet receptor recognizes a large number of ligands with structural and functional diversities to modulate different amplitudes of downstream signaling pathway(s). The human sweet-taste receptor has been extremely difficult to study by biophysical methods due to inadequate methods for producing large homogeneous quantities of the taste-receptor protein and a lack of reliable in vitro assays to precisely measure productive ligand binding modes leading to activity upon their interactions with the receptor protein. We report a multimodal high throughput assays to monitor ligand binding, receptor stability and conformational changes to model the molecular interactions between ligand-receptor. We applied saturation transfer difference nuclear magnetic resonance spectroscopy (STD-NMR) complemented by differential scanning calorimetry (DSC), circular dichroism (CD) spectroscopy and molecular docking simulations to characterize and dissect binding interactions. Our method using complementary NMR-STD and biophysical analysis is advantageous to study the mechanism of ligand binding and signaling processes in other GPCRs.