CRISPR has ushered in the era of genomic medicine. A line of powerful tools has been developed from the popular CRISPR-Cas9 to cure genetic diseases. However, there is a last-mile problem – these tools need to be effectively delivered into every cell of the patient, and most Cas9s are too big to be fitted into popular genome therapy vectors, such as the adenovirus-associated virus (AAV). In new research, Cornell scientists provide an explanation for how this problem is solved by nature: they define with atomic precision how a transposon-derived system edits DNA in RNA-guided fashion. Transposons are mobile genetic elements inside bacteria. A lineage of transposon encodes IscB, which is less than half the size of Cas9 but equally capable of DNA editing. Replacing Cas9 with IscB would definitively solve the size problem. CRISPR-Cas9 systems use an RNA as a guide to recognize a sequence of DNA. When a match is found, the Cas9 protein snips the target DNA at just the right place; it’s then possible to do surgery at the DNA level to fix genetic diseases. The cryo-EM data gathered by the Cornell team show that the IscB-ωRNA system works in a similar way, with its smaller size achieved by replacing parts of the Cas9 protein with a structured RNA (ωRNA) which is fused to the guide RNA. By replacing protein components of the larger Cas9 with RNA, the IscB protein is shrunken to the core chemical reaction centers which snip the target DNA.
Here you can see the cryoEM structure of the mini CRISPR IscB protein (surface representation) in complex with the guiding ωRNA (yellow strand) that is targeting a DNA molecule (green and red strands) (PDB code: 8CTL)
#molecularart ... #immolecular ... #minicrispr ... #ωRNA ... #geneediting ... #IscB ... #transposon ... #cryoem
Structure of the mini-CRISPR system rendered with @proteinimaging and represented with @corelphotopaint
Here you can see the cryoEM structure of the mini CRISPR IscB protein (surface representation) in complex with the guiding ωRNA (yellow strand) that is targeting a DNA molecule (green and red strands) (PDB code: 8CTL)
#molecularart ... #immolecular ... #minicrispr ... #ωRNA ... #geneediting ... #IscB ... #transposon ... #cryoem
Structure of the mini-CRISPR system rendered with @proteinimaging and represented with @corelphotopaint
