The acronym CRISPR has become synonymous with DNA editing in recent years, taking center stage in the molecular geneticist’s toolbox as a way to pinpoint the genetic code and then finely chop it up.
In its original function as an immunogen in bacteria, the CRISPR/Cas system looks for known genes from invading viruses and inactivates them.
Scientists at the University of Rochester and Cornell University in Ithaca in the US have found that a popular gene-editing tool does more for bacteria than just cuts DNA; It also coordinates with other proteins to create a defense against invading viruses.
Activation of funnel-shaped proteins called Csx28 impairs the permeability of the bacterial membrane, making it difficult for viral DNA to enter the cellular machinery and replicate. The discovery, published in the journal Science, “is unexpected and raises many new questions,” says University of Rochester biochemist Mark Dumont, co-author of the study.
“While this has no immediate medical relevance or application, the implications of this could be very important,” Dumont says.
The study involved a series of experiments in which Escherichia coli was infected with a virus that infects a bacterium or phage called Enterobacteriaceae λ phage.
This phage attaches itself to the surface of a bacterial cell and injects its DNA into it to make copies of itself.
coli using CRISPR technology to detect a threat by matching DNA repeats of previously detected phages, and then using the Cas13b enzyme to cut the invading DNA into pieces.
The researchers found that the virus replicated slowly when Csx28 was present inside the bacteria.
This protein only works with Cas13b, suggesting that they coordinated with each other to render the virus harmless.
When both Cas13b and Csx28 were present, the proportion of infected bacteria releasing infectious viral particles decreased from about 19% to about 3%, and a significant reduction in phages per milliliter was observed. In other words, the virus could not reproduce as usual.
The researchers studied the structure of the Csx28 protein using cryoelectron microscopy and found that it looks like a funnel with a hole in the center.
This increased the likelihood that the protein had formed a membrane pore and disrupted cellular metabolism, making it a hostile environment for the virus.
The researchers tested this hypothesis using a technique that causes cells to fluoresce after they lose their membrane potential, which is a small electrical charge caused by differences in ion concentrations inside and outside the cell.
They found that the two proteins together caused the membrane to depolarize, which led to an influx of charged atoms, which radically changed the cell’s internal environment. After 90 minutes, depolarization by this method removed 40% of the bacteria.
Source: Science Alert