Mapping sugar

A new technique makes it possible to image the spatial structure of polysaccharides using a scanning tunnelling microscope

July 06, 2020

There is a new perspective on sugar. A team of scientists from the Max Planck Institute for Solid State Research and the Max Planck Institute of Colloids and Interfaces has used a scanning tunnelling microscope to image how individual polysaccharide molecules are folded for the first time. The researchers are thus making it possible to investigate the relationship between the spatial structure of polysaccharides such as those found on pathogens and their biological effect.

Function follows form. To a certain extent, the opposite of this guideline mainly followed by Bauhaus designers applies in biology: the form of a biomolecule determines its function. This has long been known about enzymes and other proteins that fulfil their tasks only once they are properly folded. “But until now, it was unclear whether polysaccharides also fold like proteins”, says Peter Seeberger, Director at the Max Planck Institute of Colloids and Interfaces in Potsdam and professor at the Freie Universität Berlin. “We have now found a way to investigate this question”. And indeed: Some polysaccharides such as cellulose do fold, while others such as mannose on the surface of corona viruses or HIV do not.

Sugars under the microscope: a research team including sientists at the Max Planck Institutes for Solid State Research and for Colloids and Interfaces, have developed a method of analysing the three-dimensional structure  – chemists refer to it as the conformation – of individual molecules of polysaccharides with a scanning tunneling microscope, indicated by the tip at the top right of the picture. This produces images such as seen at the bottom of the illustration. The differences in brightness in these images shed light on the spatial arrangement of the individual building blocks in the polysaccharides. The method thus enables the correlation between the structure and biological effect of sugars to be investigated, for example on the surface proteins of viruses (top left). While these sugar structures are still unknown, it can be safely assumed that they will not have the shape of lollipops!

The sugar specialists led by Peter Seeberger owe their findings on the conformation of polysaccharides to a new method developed by a team led by Klaus Kern, Director at the Max Planck Institute for Solid State Research in Stuttgart. “Scanning tunnelling microscopy allows us to image individual sugar molecules”, says Kern. “Other methods reveal only the average structure of the sample molecules”. But an average structure is of little use, especially for investigations into how the biological function of sugars depends on their form.

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