Sensitivity enhancement of homonuclear multidimensional NMR correlations for labile sites in proteins, polysaccharides, and nucleic acids

Mihajlo Novakovic,Harald Schwalbe,Lucio Frydman,Darón I Freedberg,Ēriks Kupče,Marcos D Battistel,Andreas Oxenfarth

doi:10.1038/s41467-020-19108-x

Abstract

Multidimensional TOCSY and NOESY are central experiments in chemical and biophysical NMR. Limited efficiencies are an intrinsic downside of these methods, particularly when targeting labile sites. This study demonstrates that the decoherence imparted on these protons through solvent exchanges can, when suitably manipulated, lead to dramatic sensitivity gains per unit time in the acquisition of these experiments. To achieve this, a priori selected frequencies are encoded according to Hadamard recipes, while concurrently subject to looped selective inversion or selective saturation procedures. Suitable processing then leads to protein, oligosaccharide and nucleic acid cross-peak enhancements of ≈200–1000% per scan, in measurements that are ≈10-fold faster than conventional counterparts. The extent of these gains will depend on the solvent exchange and relaxation rates of the targeted sites; these gains also benefit considerably from the spectral resolution provided by ultrahigh fields, as corroborated by NMR experiments at 600 MHz and 1 GHz. The mechanisms underlying these experiments’ enhanced efficiencies are analyzed on the basis of three-way polarization transfer interplays between the water, labile and non-labile protons, and the experimental results are rationalized using both analytical and numerical derivations. Limitations as well as further extensions of the proposed methods, are also discussed.

Highlights

Multidimensional TOtal Corelation SpectroscopY (TOCSY) and NOESY are central experiments in chemical and biophysical NMR
The present study brings this compressed-sensing scheme to bear within the framework of Magnetization transfer (MT) experiments targeting labile 1Hs in biomolecules; thanks to continuous repolarizations with a replenishing solvent pool, this is shown to substantially improve the signal-to-noise ratio (SNR) in basic NOESY and TOCSY experiments involving such sites
The resulting asymmetry leads to potentially significant SNR/unit_time gains, as illustrated in Fig. 1b with overlaid conventional and Hadamard-encoded MT (HMT)-encoded NOESY and TOCSY

Summary

Introduction

Multidimensional TOCSY and NOESY are central experiments in chemical and biophysical NMR. By selectively addressing only the targeted 1Hs and avoiding water perturbation L-PROSY exploits some elements of SOFAST NMR21,22; at the same time, by its repeated action, it is reminiscent of CEST-based polarization transfer[23,24,25,26] Despite their sensitivity gains, L-PROSY experiments are still long, requiring traditional t1 evolution periods to build-up multidimensional information. The present study demonstrates a new approach capable of alleviating both drawbacks while achieving even more complete MTs, which relies on Hadamard-encoded[27,28,29] selective polarization transfers from the targeted labile 1Hs. It is shown that, whether involving multiple selective inversions or a continuous saturation procedure, this provides the highest per-scan enhancements we have seen on either conventionally- or L-PROSY-encoded NOESY and TOCSY experiments involving labile or fast-relaxing 1Hs. When combined with the compressed-sensing advantages and multiplexing provided by Hadamard encoding, gains of ca. The physical principles underlying these gains are described on the basis of a simple multi-site exchange model, leading to analytical descriptions that are generalized by numerical calculations, and which reproduce well the experimental observations

Methods

Results

Conclusion