Efficient 18.8 T MAS-DNP NMR reveals hidden side chains in amyloid fibrils

• Published in: Journal of biomolecular NMR Vol. 77; no. 3; pp. 121 - 130
• Main Authors: Lends, Alons, Birlirakis, Nicolas, Cai, Xinyi, Daskalov, Asen, Shenoy, Jayakrishna, Abdul-Shukkoor, Muhammed Bilal, Berbon, Mélanie, Ferrage, Fabien, Liu, Yangping, Loquet, Antoine, Tan, Kong Ooi
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.06.2023; Springer Nature B.V; Springer Verlag
• Subjects: Amyloid - chemistry; Amyloidogenic Proteins; Biochemistry; Biochemistry, Molecular Biology; Biological and Medical Physics; Biophysics; Experiments; Fibrils; Hyperpolarization; Life Sciences; Low temperature; Low temperature environments; Magnetic Resonance Imaging; Magnetic Resonance Spectroscopy - methods; NMR; Nuclear magnetic resonance; Nuclear Magnetic Resonance, Biomolecular - methods; Physics; Physics and Astronomy; Proteins; Room temperature; Segments; Sensitivity; Spectroscopy/Spectrometry; Structural Biology; Structural members; Temperature; Solid-state NMR; Amyloid fibrils; Dynamic nuclear polarization; Solid-State NMR; Amyloid Fibrils; Dynamic Nuclear Polarization
• ISSN: 0925-2738; 1573-5001
• DOI: 10.1007/s10858-023-00416-5

Amyloid fibrils are large and insoluble protein assemblies composed of a rigid core associated with a cross-β arrangement rich in β-sheet structural elements. It has been widely observed in solid-state NMR experiments that semi-rigid protein segments or side chains do not yield easily observable NMR signals at room temperature. The reasons for the missing peaks may be due to the presence of unfavorable dynamics that interfere with NMR experiments, which result in very weak or unobservable NMR signals. Therefore, for amyloid fibrils, semi-rigid and dynamically disordered segments flanking the amyloid core are very challenging to study. Here, we show that high-field dynamic nuclear polarization (DNP), an NMR hyperpolarization technique typically performed at low temperatures, can circumvent this issue because (i) the low-temperature environment (~ 100 K) slows down the protein dynamics to escape unfavorable detection regime, (ii) DNP improves the overall NMR sensitivity including those of flexible side chains, and (iii) efficient cross-effect DNP biradicals (SNAPol-1) optimized for high-field DNP (≥ 18.8 T) are employed to offer high sensitivity and resolution suitable for biomolecular NMR applications. By combining these factors, we have successfully established an impressive enhancement factor of ε ~ 50 on amyloid fibrils using an 18.8 T/ 800 MHz magnet. We have compared the DNP efficiencies of M-TinyPol, NATriPol-3, and SNAPol-1 biradicals on amyloid fibrils. We found that SNAPol-1 (with ε ~ 50) outperformed the other two radicals. The MAS DNP experiments revealed signals of flexible side chains previously inaccessible at conventional room-temperature experiments. These results demonstrate the potential of MAS-DNP NMR as a valuable tool for structural investigations of amyloid fibrils, particularly for side chains and dynamically disordered segments otherwise hidden at room temperature.