Discoveries map out CRISPR-Cas defence systems in bacteria

Model of the CSX1 protein complex

For the first time, researchers at the University of Copenhagen have mapped how bacterial cells trigger their defence against outside attacks. This could affect how diseases are fought in the future.

With the aid of highly advanced microscopes and synchrotron sources, researchers from the University of Copenhagen have gained critical insight into how bacteria function as defence mechanisms against attacks from other bacteria and viruses. The study, which has just been published in the renowned journal, Nature Communications, also describes how the defence systems can be activated on cue. This discovery can turn out to be an important cornerstone in fighting diseases in the future.

The researchers have shown how a cell attacked by a virus activates a molecule called COA (Cyclic Oligoadenylate), which in turn activates a so-called protein complex called CSX1 to eradicate the attacker.

Professor Guillermo Montoya from Novo Nordisk Foundation Center for Protein Research at the Faculty of Health and Medical Science explains: – We can see how CSX1 is activated, rotates and starts defending the cell, once COA is activated. Expressed in popular terms, the CSX1 starts cutting up the intruder.

Can help fight disease

The researchers at the University of Copenhagen have also managed to activate the process themselves successfully. In simplified terms, they sent a COA molecule after the protein complex and thus started the defence mechanism.

– In short, we have found a switch that turns on the cell’s defence system when we want it to, and so we can diffuse possible attacks, Guillermo Montoya elaborates.

It is the first time that researchers have managed to map and activate a bacterial immune system.

– A few years ago, science was not even aware that bacteria had some sort of immune defence system. With this discovery, we have come a great deal further in terms of understanding these mechanisms, Guillermo Montoya says.

Furthermore, the discovery is exciting because the defence system in bacteria resembles, in many ways, the human innate immune system.

– Therefore, it is also a step along the way of understanding the human immune system better as well as knowing how to fight bacteria and defend oneself against viruses and in the long run even multiple resistance, Guillermo Montoya says.

Minimal molecules and huge magnifying glasses

The discovery of a bacteria defence system was made possible by using x-ray crystallography at the synchrotrons Swiss Light Source in Switzerland and MAX IV in Sweden. Synchrotrons can be described as huge magnifying glasses which gives the scientists the opportunity to see details down to a molecular or even atomic scale.

Uwe Mueller,  a structural biologist and beamline scientist at BioMAX, says: “Within this research project, experimental data obtained first at BioMAX of MAX IV, data from a beamline of the Paul Scherrer Institute in Switzerland and cryo-electron microscope data have been combined in a clever way to decipher the structure-function relationship of CSX1. The complementarity of the chosen experimental methods was key for the success of the study. It is great that BioMAX could contribute to this result.”

The image of the CSX1 protein complex was made possible by the advanced cryogenic electron microscope at the University of Copenhagen’s high tech CryoEM facility.

– CSX1 is approximately 0.00005 mm long. This equates cutting one millimetre into 10,000 slices and then placing five pieces on top of each other. We have taken the pictures one by one and made a short film that reveals the activity inside CSX1, Guillermo Montoya explains.

Novo Nordisk Fonden supports the work with uncovering defence mechanisms in bacteria, and it is a collaboration between Novo Nordisk Center for Protein Research at the Faculty of Health and Medical Science and the Danish Archea Center at the Faculty of Science headed by Professor Qunxin She and Lund University.

Read the article here.

Structure of Csx1-cOA4 complex reveals the basis of RNA decay in Type III-B CRISPR-Cas

Rafael Molina, Stefano Stella, Mingxia Feng, Nicholas Sofos, Vykintas Jauniskis, Irina Pozdnyakova, Blanca López-Méndez, Qunxin She & Guillermo Montoya