Integration of 17O into the Biomolecular Toolkit

Published September 11, 2023

17O is now added to the NMR toolkit, along with 1H, 13C and 15N, to characterize biomolecules like peptides, proteins, and enzymes.

Prof. Gang Wu, Queens' University, Canada

Combining high magnetic fields, specialized probes, and measurement techniques, this work adds the crucial ¹⁷O nucleus into the study of biomolecules like peptides, proteins, and enzymes.

What did scientists discover?

MagLab users and researchers have developed an experimental protocol and state-of-the-art nuclear magnetic resonance (NMR) instrumentation that integrates ¹⁷O into the solid-state NMR toolkit for investigating biomolecules like peptides, proteins, and enzymes. The addition of ¹⁷O represents the last "piece of the puzzle", which alongside of NMR of nuclei like ¹H, ¹³C and ¹⁵N, enables the structural characterization of biomolecules.

Why is this important?

The elements oxygen, hydrogen, carbon, and nitrogen together form the peptide backbones of proteins. But of the four atoms comprising proteins, only H, C, and N atoms have widely been used for protein structure determination using solid-state NMR spectroscopy. The oxygen atoms have so far been the missing piece, since ¹⁷O NMR spectra have weak signals and poor resolution.

Oxygen NMR can help scientists study and understand the structural environments of oxygen atoms, including chemical bonds formed with other molecules and proteins. But oxygen has only only one NMR-active isotope, ¹⁷O, which has low natural abundance (0.037%). Furthermore, ¹⁷O has a nuclear spin of I = 5/2, meaning it is a quadrupolar nucleus (I > ½); this can result in interactions that produce very broad peaks in ¹⁷O solid-state NMR spectra. These two factors make NMR experiments on ¹⁷O much more difficult than those on more "NMR friendly" nuclei with I = 1/2, like ¹H, ¹³C, and ¹⁵N.

This new protocol uses a special device called an ultrafast magic-angle spinning NMR probe, which was built in-house at the MagLab and allows detection of ¹⁷O indirectly via protons (¹H). The strong ¹H NMR signal helps to overcome the issues of poor sensitivity and low resolution, enabling the addition of ¹⁷O to the NMR toolkit for biomolecules. Special peptides enriched with ¹⁷O, ¹³C and ¹⁵N were necessary for this study, and produced by the MIT group using an efficient synthetic labeling method.

Who did the research?

Ivan Hung¹, Eric G. Keeler², Wenping Mao¹, Peter L. Gor'kov¹, Robert G. Griffin², Zhehong Gan¹

¹National High Magnetic Field Laboratory; ²Massachusetts Institute of Technology.

Why did they need the MagLab?

This work uses an 18.8T magnetic field and a special magic-angle spinning NMR probe built at the MagLab that can spin the NMR sample container up to ~100kHz (i.e., it rotates 100,000 times per second). The high magnetic field and ultrafast sample spinning are critical for enhancing both the 1H NMR signal and resolution, which, in turn, is crucial for indirect ¹⁷O detection.