cold shower

Using a stream of polarized water opens up new possibilities for studying biological molecules using nuclear magnetic resonance

"We are often accused of not being sensitive enough," says Prof. Lucio Friedman from the Department of Chemical and Biological Physics at the Weizmann Institute of Science. Prof. Friedman is not talking about emotional detachment, but about nuclear magnetic resonance (NMR) - an imaging and spectroscopy tool used to study the structure of molecules and their dynamics at atomic resolution. NMR is widely used in biological and chemical research, but at the same time is notorious for its weak signals. In recent years, Prof. Friedman and the members of his research group have developed an NMR method for studying biomolecules under physiological conditions, which has a sensitivity several hundred times higher than the methods used today - high enough to capture changes in the organization of biomolecules at concentrations significantly lower than those normally tested. The researchers hope that the development will promote research in biomolecules, in particular RNA molecules and proteins.

Similar to the more familiar magnetic resonance imaging (MRI) - which is actually a certain type of NMR - nuclear magnetic resonance is based on the activation of magnetic fields to "arrange" the nuclei of the atoms in the sample and thus track them. However, the magnetic interactions are very weak - which makes MRI an incredibly non-invasive tool, but at the same time deprives NMR of the sensitivity required for imaging the dynamics of biomolecules. One option for increasing sensitivity, Prof. Friedman explains, is nuclear hyperpolarization - that is, superpolarization that significantly increases the number of spins of the atomic nuclei that line up under the influence of the magnetic fields in the sample being tested. But nuclear hyperpolarization usually requires cooling to very low temperatures that are not suitable for working with biological molecules such as DNA, RNA or proteins - especially when the goal is to study them under natural and physiological conditions.

In recent years, Prof. Friedman's research group has been dealing with this problem from a new angle: they are trying to apply hyperpolarization in biological molecules with the help of water, or more precisely, hyperpolarization of the hydrogen nuclei in water molecules at a temperature close to absolute zero and then spraying them on biological molecules under physiological conditions . In this process, the polarized (and frozen) water must be melted at once and flowed into a test tube where the biomolecules being studied are waiting in a standard NMR array. Under the right conditions, the hydrogen atoms in water spontaneously exchange with their counterparts in biomolecules - quickly jumping between the oxygen atoms of the water and the nitrogen atoms in DNA or proteins. This substitution does not affect the superpolarization of the hydrogen nuclei, and every time a biomolecule receives a polarized nucleus from the water, it emits an amplified signal, the intensity of which is several hundred times stronger than a normal NMR reaction. Prof. Friedman, research student Miahlo Novkovic and postdoctoral researcher Dr. Gregory Olsen took advantage of this phenomenon, and in collaboration with researchers from Frankfurt "photographed" at a rate of about three pictures per second the dynamics of molecules known as riboswitches - bits of RNA -messenger islands that rapidly switch from one state to another when they are activated by the binding of a small molecule.

"The most important thing we learned is 'not to touch the water' from the moment the sample was injected," says Prof. Friedman. "The water acts as a kind of bank of hyperpolarized nuclei for the biological molecules, and the cold shower allows these molecules to be studied for a minute or two using different NMR approaches."

To conduct these experiments, the researchers used two NMR systems, both at the Weizmann Institute of Science. One, which was operated at extremely low temperatures and was used to hyperpolarize the water, and the other - where RNA molecules were kept under physiological conditions. The planning of the experiment and the preparation of the samples were carried out in collaboration with the research group of Prof. Harald Schwalbe at the Goethe University in Frankfurt.

Now, having demonstrated the advantages of using hyperpolarized water, the researchers intend to continue developing the method: to extend the NMR experiments to more complex biomolecules, including other RNA molecules and proteins, as well as to conduct experiments that will reach even higher levels of hyperpolarization.

The method developed by the scientists makes it possible to increase the sensitivity of nuclear magnetic resonance more than 300 times and to study the dynamics of biological molecules with a time resolution of less than a second and at a temperature of 36 degrees.

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