How to see small biomolecules in a living cell

Biologists have created labels for individual amino acids and nucleotides

<url>Scientists from Columbia University have developed a technology for monitoring the movement of low-molecular-weight substances in cells whose size does not allow the use of conventional fluorescent labels.

The study was published in the journal Nature Methods (Live-cell imaging of alkyne-tagged small biomolecules by stimulated Raman scattering), briefly about it can be read in the university press release: Imaging dynamics of small biomolecules inside live cells.

To track low molecular weight substances, scientists decided to use Raman scattering (Raman effect). During this scattering, the vibrational energy of the molecules is exchanged for radiation energy, as a result of which lines appear in the spectrum that were not in the exciting light.

The key for the new method is the use of alkyl labels, that is, chemical groups with a triple carbon-carbon bond. Substances with such bonds are practically absent in cells, while they are very clearly visible in the Raman spectrum. In addition, unlike fluorescent groups, alkyl groups have many times smaller size, which means they have less influence on the behavior of labeled molecules.

By adding amino acids with alkyl labels to the medium, for example, and then scanning the cells with a laser, you can see how the labeled amino acids move, where they are concentrated and which proteins they are included in. Scientists have shown that alkyl groups are suitable for labeling both amino acids and DNA and RNA monomers, fatty acids and other low molecular weight substances.

Image: Lu Wei et al., Nature Methods, 2014

Fluorescent labeling is one of the key methods of modern biology. In this case, two approaches to labeling are used: either chemical, where a label (for example, fluorescin) is attached to the desired substance in advance, or, in the case of proteins, genetic, when the desired genes are merged with sequences of fluorescent proteins (GFP) in advance, as a result of which labeled proteins are formed directly in the cell. Both types of labels are usually very bulky and are not suitable for molecules such as individual amino acids, sugars, lipids, nucleotides, and so on.

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