An international team of scientists has taken a great step forward in our understanding of how enzymes "edit" genes, paving the way to correct genetic diseases in patients.
Researchers from the Universities of Bristol, Münster and the Biotechnology Institute of Lithuania have observed the process by which a class of enzymes called CRISPR, which is pronounced & # 39; crispy & # 39 ;, binds and alters the structure of DNA.
The results, published today in the Proceedings of the National Academy of Sciences (PNAS), provide a vital piece of the puzzle if these genome editing tools will eventually be used to correct genetic diseases in humans.
CRISPR enzymes were first discovered in bacteria in the 1980s as an immune defense used by bacteria against invading viruses. Scientists have shown more recently that one type of CRISPR enzyme, Cas9, can be used to edit the human genome, the complete set of genetic information. for humans
These enzymes have been designed to accurately target a single combination of letters within the three billion base pairs of the DNA molecule. This amounts to correcting a single misspelled word in an encyclopedia of 23 volumes.
To find this needle in a haystack, CRISPR enzymes use an RNA molecule, a nucleic acid with a structure similar to DNA. The selection process requires that CRISPR enzymes separate the DNA strands and insert the RNA to form a specific sequence structure called & # 39; R-loop & # 39 ;.
The global team tested the R-loop model using specially modified microscopes in which individual DNA molecules are stretched in a magnetic field. By altering the torsional force in the DNA, the researchers were able to directly monitor the events of R-loop formation by individual CRISPR enzymes.
This allowed them to reveal previously hidden steps in the process and test the influence of the DNA base sequence.
Professor Mark Szczelkun, from the University of Bristol School of Biochemistry, said: "An important challenge to exploit these exciting genome editing tools is to ensure that only one specific location in a genome is chosen.
"Our individual molecule assays have led to a greater understanding of the influence of the DNA sequence on the formation of the R loop. In the future, this will help in the rational reengineering of CRISPR enzymes to increase their accuracy and minimize the effects outside. Of the objective". it will be vital if we are finally going to apply these tools to correct genetic diseases in patients. "