Dangerous bacteria

DANGEROUS BACTERIA

Don’t be deceived by appearances: these beautifully twisted microscopic filaments are far from harmless. They can be deadly. They are leptospirosa: bacteria that can infect man and certain animals with an infectious disease that is very common all over the world: leptospirosis.

This disease affects the liver, kidney, and meninges. In order to understand how leptospirosa infect organisms, scientists decided to make a detailed study of these bacteria.
At the SOLEIL synchrotron, a team is taking a special interest in the exposed proteins at the surface of the membrane of these bacteria.
 
Beatriz Guimaraes – Scientist on the PROXIMA 1 beamline
Here, we are trying to discover what function this protein has in the bacteria. For example, when bacteria infect the host cells, will this protein interact specifically with a protein of the host cell, and if so, how?
 
In order to identify the role of these surface proteins, scientists will try to establish the exact shape of these molecules in three dimensions, using x-rays produced by the PROXIMA 1 beamline of the SOLEIL Synchrotron.
For proteins to be studied at the atomic level using x-rays, they must be in the form of a crystal from a few microns to a few hundred microns.

Beatriz Guimaraes – Scientist on the PROXIMA 1 beamline
And now, with my little loop, I am going fishing for crystals.
There are millions of molecules of protein in a crystal.

When organised in a crystal structure like this, each protein molecule will have a similar interaction with the x-ray beam.
This x-ray/protein interaction is what the scientists are going to analyse.
The protein crystal is attached to the end of this thin stem.
The scientist has placed it on the trajectory of the x-ray beam.

Beatriz Guimaraes – Scientist on the PROXIMA 1 beamline
These black dots are the product of the interaction of the x-rays with our crystal.
The distribution and intensity of these black dots are related to the position and identity of the atoms in our crystal.
So, by analysing these images, we can then use software to calculate the position of atoms in the protein molecule.

After computer processing, the scientists obtain a very precise three-dimensional representation of the protein. All that then remains is the fine identification of the properties and specific characteristics of each part of the molecule.
For example, on this representation of the molecule, the electrically charged regions have been highlighted.

Beatriz Guimaraes – Scientist on the PROXIMA 1 beamline
The regions shown in blue have a positive charge, and those shown in red are negatively charged.
This type of information can then be related to the protein’s ability to interact, for example, with another protein or a DNA molecule.

Thanks to these studies, scientists will be able to identify which proteins bacteria use to infect an organism.

Their work could lead to the development of new, more effective vaccines, or tests to diagnose the disease in the early stages of infection, for a better chance of curing it.