Pre-Homonuclear Decoupling Enables High-Resolution NMR Analysis of Intrinsically Disordered Proteins in Solution

Pure shift amide detection in conventional and TROSY-type experiments of 13C,15N-labeled proteins

Large coupling networks in uniformly ¹³C,¹⁵N-labeled biomolecules induce broad multiplets that even in flexible proteins are frequently not recognized as such. The reason is that given multiplets typically consist of a large number of individual resonances that result in a single broad line, in which individual components are no longer resolved. We here introduce a real-time pure shift acquisition scheme for the detection of amide protons which is based on ¹³C-BIRD^r,X. As a result the full homo- and heteronuclear coupling network can be suppressed at low power leading to real singlets at substantially improved resolution and uncompromised sensitivity. The method is tested on a small globular and an intrinsically disordered protein (IDP) where the average spectral resolution is increased by a factor of ~ 2 and higher. Equally important, the approach works without saturation of water magnetization for solvent suppression and exchanging amide protons are not affected by saturation transfer.

Selective detection of protein acetylation by NMR spectroscopy

Selective detection of biomolecules and their modifications in cells is essential for understanding cell functions and diseases. We have developed an NMR pulse sequence, Ac-FIND (Acetylation-FIltered aNd eDited), which uses isotope editing/filtering techniques for selective detection of protein acetylation. Acetylation of the N-terminus and lysine side chains by N-succinimidyl acetate was selectively observed for intrinsically disordered α-synuclein and well-ordered ubiquitin. Furthermore, when nonacetylated ¹³C/¹⁵N-enriched α-synuclein was introduced into live HEK293 cells, intracellular N-terminal acetylation of α-synuclein was detected by the appearance of a single peak using Ac-FIND. This work demonstrates the utility of NMR to detect a specific protein modification both in vitro and in live cells.

Longitudinal Spin Order Labeling on Multiple Quantum Coherences Enables NMR Analysis of Intrinsically Disordered Proteins at Ultrahigh Resolution

Intrinsically disordered proteins (IDPs) play an important role in cell signaling, and NMR is well-suited to study conformational ensembles and dynamics of IDPs. However, the intrinsic flexibility of IDPs often results in severe spectral overlap, which hampers accurate NMR data analysis. By labeling the longitudinal spin order of an α proton (i.e., H^α_z) on multiple quantum coherences of backbone nuclei (e.g., N_yC'_xC^α_y), we were able to apply pre-homonuclear decoupling (PHD) to transverse relaxation-optimized spectroscopy (TROSY). The proposed scheme provides ultrahigh resolution in both amide proton and nitrogen dimensions, as illustrated in the analysis of Tau and alpha-synuclein (α-Syn) proteins. The PHD-TROSY readout enabled complete backbone resonance assignment of α-Syn using a single 3D HNCA experiment performed on a 600 MHz NMR spectrometer.

Dynamic G Protein-Coupled Receptor Signaling Probed by Solution NMR Spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for investigating various dynamic features of G protein-coupled receptor (GPCR) signaling. In this Perspective, we focus on NMR techniques to characterize ligand-dependent conformational dynamics of GPCRs as well as the interaction of GPCRs with their environment and ligands. We also describe circumstances under which each technique should be applied, their advantages and disadvantages, and how they can be combined with other strategies to deepen the understanding of GPCR signaling at the molecular level.