There are different types of CRISPR system, and the one on which researchers have focused to describe the three-dimensional structure in detail is called CRISPR-Cas13bt3. What’s unique about it is that it’s very small. Usually, these types of molecules contain around 1,200 amino acids, whereas this one only contains around 700. Smaller size is a plus, as it allows better access and delivery to target editing sites. To obtain the three-dimensional structure, the researchers used a cryoelectron microscope to map the structure of the CRISPR system, placing the molecule on a thin layer of ice and projecting an electron beam through it to generate data which was then processed into a detailed three-dimensional model. CRISPR-Cas13bt3 is totally different from CRISPR-Cas9: the scissors are already there, but they have to hook onto the RNA strand at the right target site. To do this, it uses a binding element on those two unique loops that link the different parts of the protein together. The researchers then used their findings to refine the tool to increase its precision, and tested its activity and specificity in living cells. They found that in cell cultures, these systems were able to target much more easily.
