Biomolecular Nuclear Magnetic Resonance Research Articles

Optimal control pulses for the 1.2-GHz (28.2-T) NMR spectrometers

The ability to measure nuclear magnetic resonance (NMR) spectra with a large sample volume is crucial for concentration-limited biological samples to attain adequate signal-to-noise (S/N) ratio. The possibility to measure with a 5-mm cryoprobe is currently absent at the 1.2-GHz NMR instruments due to the exceedingly high radio frequency power demands, which is four times compared to 600-MHz instruments. Here, we overcome the high-power demands by designing optimal control (OC) pulses with up to 20 times lower power requirements than currently necessary at a 1.2-GHz spectrometer. We show that multidimensional biomolecular NMR experiments constructed using these OC pulses can bestow improvement in the S/N ratio of up to 26%. With the expected power limitations of a 5-mm cryoprobe, we observe an enhancement in the S/N ratio of more than 240% using our OC sequences. This motivates the development of a cryoprobe with a larger volume than the current 3-mm cryoprobes.

Biomolecular NMR in the AI-assisted structural biology era: Old tricks and new opportunities

Over the last 40 years nuclear magnetic resonance (NMR) spectroscopy has established itself as one of the most versatile techniques for the characterization of biomolecules, especially proteins. Given the molecular size limitations of NMR together with recent advances in cryo-electron microscopy and artificial intelligence-assisted protein structure prediction, the bright future of NMR in structural biology has been put into question. In this mini review we argue the contrary. We discuss the unique opportunities solution NMR offers to the protein chemist that distinguish it from all other experimental or computational methods, and how it can benefit from machine learning.

Utility of methyl side chain probes for solution NMR studies of large proteins

Selective isotopic labeling of methyl side chain groups in proteins and other biomolecules, combined with advances in perdeuteration, new pulse sequences, and high field spectrometers with cryogenic probes, has revolutionized the field of solution nuclear magnetic resonance (NMR) spectroscopy by enabling characterization of macromolecular systems with molecular weights above 1 MDa in their native aqueous environment. This tutorial provides a basic overview for how modern NMR spectroscopists can utilize methyl side chain probes to study their system of interest. The advantages and limitations of methyl side chain probes are discussed. In addition, the preparation of selectively 13C-methyl labeled recombinant protein samples, strategies for manual and automated methyl NMR resonance assignment, and the application of methyl probes for characterization of dynamics and conformational exchange are discussed. A sneak preview for ways in which methyl probes are expected to continue to advance the field of biomolecular NMR towards new horizons in solution studies of large supramolecular complexes is also presented.

Biological Magnetic Resonance Data Bank.

The Biological Magnetic Resonance Data Bank (BMRB, https://bmrb.io) is the international open data repository for biomolecular nuclear magnetic resonance (NMR) data. Comprised of both empirical and derived data, BMRB has applications in the study of biomacromolecular structure and dynamics, biomolecular interactions, drug discovery, intrinsically disordered proteins, natural products, biomarkers, and metabolomics. Advances including GHz-class NMR instruments, national and trans-national NMR cyberinfrastructure, hybrid structural biology methods and machine learning are driving increases in the amount, type, and applications of NMR data in the biosciences. BMRB is a Core Archive and member of the World-wide Protein Data Bank (wwPDB).

A method for selective 19 F-labeling absent of probe sequestration (SLAPS).

Fluorine (19F) offers several distinct advantages for biomolecular nuclear magnetic resonance spectroscopy such as no background signal, 100% natural abundance, high sensitivity, and a large chemical shift range. Exogenous cysteine‐reactive 19F‐probes have proven especially indispensable for characterizing large, challenging systems that are less amenable to other isotopic labeling strategies such as G protein‐coupled receptors. As fluorine linewidths are inherently broad, limiting reactions with offsite cysteines is critical for spectral simplification and accurate deconvolution of component peaks—especially when analyzing systems with intermediate to slow timescale conformational exchange. Here, we uncovered noncovalent probe sequestration by detergent proteomicelles as a second source of offsite labeling when using the popular 19F‐probe BTFMA (2‐bromo‐N‐(4‐[trifluoromethyl]phenyl)acetamide). The chemical shift and relaxation rates of these unreacted 19F‐BTFMA molecules are insufficient to distinguish them from protein‐conjugates, but they can be easily identified using mass spectrometry. We present a simple four‐step protocol for Selective Labeling Absent of Probe Sequestration (SLAPS): physically disrupt cell membranes in the absence of detergent, incubate membranes with cysteine‐reactive 19F‐BTFMA, remove excess unreacted 19F‐BTFMA molecules via ultracentrifugation, and finally solubilize in the detergent of choice. Our approach builds upon the in‐membrane chemical modification method with the addition of one crucial step: removal of unreacted 19F‐probes by ultracentrifugation prior to detergent solubilization. SLAPS is broadly applicable to other lipophilic cysteine‐reactive probes and membrane protein classes solubilized in detergent micelles or lipid mimetics.

Synthesis of lanthanide tag and experimental studies on paramagnetically induced residual dipolar couplings

Nuclear Magnetic Resonance (NMR) spectroscopy is an indispensable technique for the structure elucidation of molecules and determination of their characteristic interactions. Residual Dipolar Coupling (RDC) is an NMR parameter that provides global orientation information of molecules but necessitates the use of an anisotropic orientation medium for the partial alignment of the target molecule with respect to the magnetic field. Importantly, anisotropic paramagnetic tags have been successful as orienting media in biomolecular NMR applications but their use in small organic molecules remains imperfect due to challenges in designing functional lanthanide complexes with varying degrees of bonding in the Ln(III) inner coordination sphere. In this study, we propose a strategy for the synthesis of the lanthanide tag 4-mercaptomethylpyridine-2,6-dicarboxylic acid, 4-MMDPA and the measurement of RDCs in a target molecule using several paramagnetic lanthanide complexes.Graphical

Correction of field instabilities in biomolecular solid-state NMR by simultaneous acquisition of a frequency reference.

With the advent of faster magic-angle spinning (MAS) and higher magnetic fields, the resolution of biomolecular solid-state nuclear magnetic resonance(NMR) spectra has been continuously increasing. As a direct consequence, the always narrower spectral lines, especially in proton-detected spectroscopy, are also becoming more sensitive to temporal instabilities of the magnetic field in the sample volume. Field drifts in the order of tenths of parts per million occur after probe insertion or temperature change, during cryogen refill, or are intrinsic to the superconducting high-field magnets, particularly in the months after charging. As an alternative to a field-frequency lock based on deuterium solvent resonance rarely available for solid-state NMR, we present a strategy to compensate non-linear field drifts using simultaneous acquisition of a frequency reference (SAFR). It is based on the acquisition of an auxiliary 1D spectrum in each scan of the experiment. Typically, a small-flip-angle pulse is added at the beginning of the pulse sequence. Based on the frequency of the maximum of the solvent signal, the field evolution in time is reconstructed and used to correct the raw data after acquisition, thereby acting in its principle as a digital lock system. The general applicability of our approach is demonstrated on 2D and 3D protein spectra during various situations with a non-linear field drift. SAFR with small-flip-angle pulses causes no significant loss in sensitivity or increase in experimental time in protein spectroscopy. The correction leads to the possibility of recording high-quality spectra in a typical biomolecular experiment even during non-linear field changes in the order of 0.1 ppm h without the need for hardware solutions, such as stabilizing the temperature of the magnet bore. The improvement of linewidths and peak shapes turns out to be especially important for H-detected spectra under fast MAS, but the method is suitable for the detection of carbon or other nuclei as well.

The catalytic activity of TCPTP is auto-regulated by its intrinsically disordered tail and activated by Integrin alpha-1

T-Cell Protein Tyrosine Phosphatase (TCPTP, PTPN2) is a non-receptor type protein tyrosine phosphatase that is ubiquitously expressed in human cells. TCPTP is a critical component of a variety of key signaling pathways that are directly associated with the formation of cancer and inflammation. Thus, understanding the molecular mechanism of TCPTP activation and regulation is essential for the development of TCPTP therapeutics. Under basal conditions, TCPTP is largely inactive, although how this is achieved is poorly understood. By combining biomolecular nuclear magnetic resonance spectroscopy, small-angle X-ray scattering, and chemical cross-linking coupled with mass spectrometry, we show that the C-terminal intrinsically disordered tail of TCPTP functions as an intramolecular autoinhibitory element that controls the TCPTP catalytic activity. Activation of TCPTP is achieved by cellular competition, i.e., the intrinsically disordered cytosolic tail of Integrin-α1 displaces the TCPTP autoinhibitory tail, allowing for the full activation of TCPTP. This work not only defines the mechanism by which TCPTP is regulated but also reveals that the intrinsically disordered tails of two of the most closely related PTPs (PTP1B and TCPTP) autoregulate the activity of their cognate PTPs via completely different mechanisms.

Newly elected Chinese Academy of Sciences academicians in chemistry division in 2021

Newly elected Chinese Academy of Sciences academicians in chemistry division in 2021

Virtual Homonuclear Decoupling in Direct Detection Nuclear Magnetic Resonance Experiments Using Deep Neural Networks.

Nuclear magnetic resonance (NMR) experiments are frequently complicated by the presence of homonuclear scalar couplings. For the growing body of biomolecular 13C-detected NMR methods, one-bond 13C-13C couplings significantly reduce sensitivity and resolution. The solution to this problem has typically been to perform virtual decoupling by recording multiple spectra and taking linear combinations. Here, we propose an alternative method of virtual decoupling using deep neural networks, which only requires a single spectrum and gives a significant boost in resolution while reducing the minimum effective phase cycles of the experiments by at least a factor of 2. We successfully apply this methodology to virtually decouple in-phase CON (13CO-15N) protein NMR spectra, 13C-13C correlation spectra of protein side chains, and 13Cα-detected protein 13Cα-13CO spectra where two large homonuclear couplings are present. The deep neural network approach effectively decouples spectra with a high degree of flexibility, including in cases where existing methods fail, and facilitates the use of simpler pulse sequences.

Using delayed decoupling to attenuate residual signals in editing filters.

Isotope filtering methods are instrumental in biomolecular nuclear magnetic resonance (NMR) studies as they isolate signals of chemical moieties of interest within complex molecular assemblies. However, isotope filters suppress undesired signals of isotopically enriched molecules through scalar couplings, and variations in scalar couplings lead to imperfect suppressions, as occurs for aliphatic and aromatic moieties in proteins. Here, we show that signals that have escaped traditional filters can be attenuated with mitigated sensitivity losses for the desired signals of unlabeled moieties. The method uses a shared evolution between the detection and preceding preparation period to establish non-observable antiphase coherences and eliminates them through composite pulse decoupling. We demonstrate the method by isolating signals of an unlabeled post-translational modification tethered to an isotopically enriched protein.

SsNMRlib: a comprehensive library and tool box for acquisition of solid-state nuclear magnetic resonance experiments on Bruker spectrometers.

We introduce ssNMRlib, a comprehensive suite of pulse sequences and jython scripts for user-friendly solid-state nuclear magnetic resonance (NMR) data acquisition, parameter optimization and storage on Bruker spectrometers. ssNMRlib allows the straightforward setup of even highly complex multi-dimensional solid-state NMR experiments with a few clicks from an intuitive graphical interface directly from the Bruker Topspin acquisition software. ssNMRlib allows the setup of experiments in a magnetic-field-independent manner and thus facilitates the workflow in a multi-spectrometer setting with a centralized library. Safety checks furthermore assist the user in experiment setup. Currently hosting more than 140 1D to 4D experiments, primarily for biomolecular solid-state NMR, the library can be easily customized and new experiments are readily added as new templates. ssNMRlib is part of the previously introduced NMRlib library, which comprises many solution-NMR pulse sequences and macros.

BioMagResBank (BMRB) as a Resource for Structural Biology.

The Biological Magnetic Resonance Data Bank (BioMagResBank or BMRB), founded in 1988, serves as the archive for data generated by nuclear magnetic resonance (NMR) spectroscopy of biological systems. NMR spectroscopy is unique among biophysical approaches in its ability to provide a broad range of atomic and higher-level information relevant to the structural, dynamic, and chemical properties of biological macromolecules, as well as report on metabolite and natural product concentrations in complex mixtures and their chemical structures. BMRB became a core member of the Worldwide Protein Data Bank (wwPDB) in 2007, and the BMRB archive is now a core archive of the wwPDB. Currently, about 10% of the structures deposited into the PDB archive are based on NMR spectroscopy. BMRB stores experimental and derived data from biomolecular NMR studies. Newer BMRB biopolymer depositions are divided about evenly between those associated with structure determinations (atomic coordinates and supporting information archived in the PDB) and those reporting experimental information on molecular dynamics, conformational transitions, ligand binding, assigned chemical shifts, or other results from NMR spectroscopy. BMRB also provides resources for NMR studies of metabolites and other small molecules that are often macromolecular ligands and/or nonstandard residues. This chapter is directed to the structural biology community rather than the metabolomics and natural products community. Our goal is to describe various BMRB services offered to structural biology researchers and how they can be accessed and utilized. These services can be classified into four main groups: (1) data deposition, (2) data retrieval, (3) data analysis, and (4) services for NMR spectroscopists and software developers. The chapter also describes the NMR-STAR data format used by BMRB and the tools provided to facilitate its use. For programmers, BMRB offers an application programming interface (API) and libraries in the Python and R languages that enable users to develop their own BMRB-based tools for data analysis, visualization, and manipulation of NMR-STAR formatted files. BMRB also provides users with direct access tools through the NMRbox platform.

Advances that facilitate the study of large RNA structure and dynamics by nuclear magnetic resonance spectroscopy.

The characterization of functional yet nonprotein coding (nc) RNAs has expanded the role of RNA in the cell from a passive player in the central dogma of molecular biology to an active regulator of gene expression. The misregulation of ncRNA function has been linked with a variety of diseases and disorders ranging from cancers to neurodegeneration. However, a detailed molecular understanding of how ncRNAs function has been limited; due, in part, to the difficulties associated with obtaining high‐resolution structures of large RNAs. Tertiary structure determination of RNA as a whole is hampered by various technical challenges, all of which are exacerbated as the size of the RNA increases. Namely, RNAs tend to be highly flexible and dynamic molecules, which are difficult to crystallize. Biomolecular nuclear magnetic resonance (NMR) spectroscopy offers a viable alternative to determining the structure of large RNA molecules that do not readily crystallize, but is itself hindered by some technical limitations. Recently, a series of advancements have allowed the biomolecular NMR field to overcome, at least in part, some of these limitations. These advances include improvements in sample preparation strategies as well as methodological improvements. Together, these innovations pave the way for the study of ever larger RNA molecules that have important biological function.This article is categorized under: RNA Structure and Dynamics > RNA Structure, Dynamics, and ChemistryRegulatory RNAs/RNAi/Riboswitches > Regulatory RNAsRNA Structure and Dynamics > Influence of RNA Structure in Biological Systems

Quo Vadis Biomolecular NMR Spectroscopy?

In-cell nuclear magnetic resonance (NMR) spectroscopy offers the possibility to study proteins and other biomolecules at atomic resolution directly in cells. As such, it provides compelling means to complement existing tools in cellular structural biology. Given the dominance of electron microscopy (EM)-based methods in current structure determination routines, I share my personal view about the role of biomolecular NMR spectroscopy in the aftermath of the revolution in resolution. Specifically, I focus on spin-off applications that in-cell NMR has helped to develop and how they may provide broader and more generally applicable routes for future NMR investigations. I discuss the use of ‘static’ and time-resolved solution NMR spectroscopy to detect post-translational protein modifications (PTMs) and to investigate structural consequences that occur in their response. I argue that available examples vindicate the need for collective and systematic efforts to determine post-translationally modified protein structures in the future. Furthermore, I explain my reasoning behind a Quinary Structure Assessment (QSA) initiative to interrogate cellular effects on protein dynamics and transient interactions present in physiological environments.

BCL-2 Protein Family Interaction Analysis by Nuclear Magnetic Resonance Spectroscopy.

Biomolecular nuclear magnetic resonance (NMR) is a powerful and versatile method for studying both protein-protein interactions (PPIs) and protein-small molecule binding. NMR has been used extensively in the investigation of BCL-2 family proteins revealing the structure of key family members, identifying binding partners and interaction sites, and screening small molecule modulators. In this chapter we discuss the application of NMR to identify interaction sites and structure determination of protein-protein and protein-small molecule complexes using two examples.

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

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.

Nuclear magnetic resonance structure-based drug design.

Nuclear magnetic resonance structure-based drug design.

Curating Scientific Workflows for Biomolecular Nuclear Magnetic Resonance Spectroscopy.

This paper describes our recent and ongoing efforts for enhancing the curation of scientific workflows to improve reproducibility and reusability of biomolecular nuclear magnetic resonance (bioNMR) data. Our efforts have focused on both developing a workflow management system, called CONNJUR Workflow Builder (CWB), as well as refactoring our workflow data model to make use of the PREMIS model for digital preservation. This revised workflow management system will be available through the NMRbox cloud-computing platform for bioNMR. In addition, we are implementing a new file structure which bundles the original binary data files along with PREMIS XML records describing the provenance of the data. These are packaged together using a standardized file archive utility. In this manner, the provenance and data curation information is maintained together along with the scientific data. The benefits and limitations of these approaches as well as future directions are discussed.

Off-resonance NOVEL.

Dynamic nuclear polarization (DNP) is theoretically able to enhance the signal in nuclear magnetic resonance (NMR) experiments by a factor γe/γn, where γ's are the gyromagnetic ratios of an electron and a nuclear spin. However, DNP enhancements currently achieved in high-field, high-resolution biomolecular magic-angle spinning NMR are well below this limit because the continuous-wave DNP mechanisms employed in these experiments scale as ω0-n where n ∼ 1-2. In pulsed DNP methods, such as nuclear orientation via electron spin-locking (NOVEL), the DNP efficiency is independent of the strength of the main magnetic field. Hence, these methods represent a viable alternative approach for enhancing nuclear signals. At 0.35 T, the NOVEL scheme was demonstrated to be efficient in samples doped with stable radicals, generating 1H NMR enhancements of ∼430. However, an impediment in the implementation of NOVEL at high fields is the requirement of sufficient microwave power to fulfill the on-resonance matching condition, ω0I = ω1S, where ω0I and ω1S are the nuclear Larmor and electron Rabi frequencies, respectively. Here, we exploit a generalized matching condition, which states that the effective Rabi frequency, ω1Seff, matches ω0I. By using this generalized off-resonance matching condition, we generate 1H NMR signal enhancement factors of 266 (∼70% of the on-resonance NOVEL enhancement) with ω1S/2π = 5 MHz. We investigate experimentally the conditions for optimal transfer of polarization from electrons to 1H both for the NOVEL mechanism and the solid-effect mechanism and provide a unified theoretical description for these two historically distinct forms of DNP.