Specifically, CASANOVA stands for “CRISPR-Cas9 activity switching via a novel optogenetic variant of AcrIIA4.” Anti-CRISPR proteins are small proteins from bacteria-infecting viruses that are able to bind the CRISPR gene scissors. When bound, the gene scissors are blind and no longer able to reach their target sequence in the genetic material. This means the viral genome is protected from attacks by the gene scissors.
A team of researchers under Dr. Dominik Niopek, Group Leader of Synthetic Biology at the Institute of Pharmacy and Molecular Biotechnology and the BioQuant Center of Heidelberg University, and Dr. Roland Eils, Professor of Digital Health at Berlin Institute of Health (BIH) and Charité – Universitätsmedizin Berlin and Director of the Health Data Science Unit at Heidelberg University Hospital, modified anti-CRISPR proteins with the help of genetic engineering methods so that they could be switched on and off – with light. To do this, the researchers integrated a molecular light sensor from the oat plant into an anti-CRISPR protein. They then introduced the produced hybrid protein – called CASANOVA – into human cell cultures with the help of the CRISPR gene scissors.
“In the dark, CASANOVA efficiently binds to the CRISPR gene scissors, thereby switching them off,” explains Niopek. “But when blue light hits the protein pair in the cell, the romance comes to an abrupt end. The gene scissors are released from the anti-CRISPR protein, thereby becoming active.”
With their method, the researchers working under Niopek and Eils were able to selectively change the genome sequence in human cells through external illumination. CASANOVA has also made it possible to switch genes on and off at the touch of a button. The binding dynamics of the CRISPR gene scissors to their target sequence in the genetic material of living cells could even be followed live by the scientists under the microscope.
“CASANOVA is not only an innovative tool for basic research, for example, to study the interaction between the activity of genes and the behavior of cells. The method could also become relevant in the future for particularly precise therapies used to treat genetic diseases,” explains Eils.
“CASANOVA’s versatility and ease of use are key advantages over previous CRISPR-Cas9 control methods,” adds Felix Bubeck. Together with Mareike Hoffmann, a PhD student at the German Cancer Research Center (DKFZ), he conducted many of the crucial experiments in Niopek and Eils’ laboratory. Bubeck is a student in the Molecular Biotechnology Master’s program at Heidelberg University and co-first author of the publication.
Bubeck*, Hoffmann* et al. (2018): Engineered anti-CRISPR proteins for optogenetic control of CRISPR/Cas9. Nature Methods. DOI: 10.1038/s41592-018-0178-9