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Scientists: new version of DNA editor changes genome with 100% accuracy
American molecular biologists have presented to the world a new version of the revolutionary CRISPR/Cas9 genomic editor, which changes DNA with almost 100% accuracy and rarely makes unnecessary "edits" to the genome structure, according to an article published in the journal Science (Slaymaker et al., Rationally engineered Cas9 nucleases with improved specificity).
"Most of the concerns related to the safety of CRISPR/Cas9 are related to the fact that this system can make changes to unnecessary regions of the genome. We hope that the creation of eSpCas9 will neutralize some of these concerns, but of course, this protein is not a panacea. The field of genomic editing is developing rapidly, and we still have a lot to learn before we can put it into practice," said Feng Zhang from the Massachusetts Institute of Technology (in a press release from Broad, MIT scientists overcome key CRISPR–Cas9 genome editing hurdle - VM).
Zhang and his colleagues are the developers of a revolutionary genome editing system – CRISPR/Cas9, which allows arbitrary deletion and replacement of individual genes and DNA fragments. The first versions of this technology appeared in 2013, when Zhang and his colleagues realized that the "antivirus" built into the bacteria Streptococcus pyogenes – the CRISPR system – could be used, together with another bacterial protein, DNA scissors Cas9, to edit the genome.
In 2013, the rapid development of this technology began, and today it has been used to edit the genomes of dozens of living beings, including human embryos, which Chinese geneticists confessed in April this year. These experiments revealed the main drawback of CRISPR/Cas9 – the "editor", especially with multiple gene changes, sometimes made mistakes and deleted unnecessary DNA segments.
Such behavior is permissible during genetic experiments in the laboratory, but is unacceptable in medical practice, where such a typo can cost the life of a person in whose DNA a "surgical intervention" is performed.
Zhang and his colleagues have spent the last two years trying to find ways to make Cas9 not interfere with the work of those parts of the genome that do not need editing. The fruit of their efforts was a new protein eSpCas9, the structure of which differs from the original by only three "letters"-amino acids.
These changes, as Zhang says, made the enzyme more fastidious – now it does not begin to cut DNA in cases when the RNA "template" containing the "negative" of the gene being cut only partially coincides with the desired sequence of genetic "letters"-nucleotides.
Zhang's team was able to achieve this due to the fact that scientists have well studied how the nucleotide strand binds to Cas9 and how this process is influenced by the charges of the DNA molecule and the enzyme itself, which allowed them, using a computer, to pick up such changes in the structure of the protein that it became weaker to bind to incorrectly connected RNA "templates".
Drawing from an article in Science – VM
As shown by the first experiments with eSpCas9, this version of the protein allows to achieve an actual 100% accuracy of genome editing, which in principle allows the use of CRISPR/eSpCas9 for fine "molecular surgery" and potential clinical purposes.
Zhang himself warns that it is too early to talk about this – to solve such problems, additional checks of the reliability of eSpCas9 are required, as well as a comprehensive discussion of the ethical aspects of genome editing. To stimulate discussion and experiments, scientists have opened the "source code" of eSpCas9, which will allow molecular biologists from around the world to test the work of a new version of the protein and try to find flaws in the development of Zhang and his colleagues.
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02.12.2015