New CRISPR Tool Holds Potential for Combatting Viruses

[seqadmin]

Small in size but mighty in precision is how one could describe the latest work from Rice University scientists on CRISPR systems, the renowned technology that edits nucleic acids like RNA and DNA. Their latest publication in Nature Communications goes in-depth about the three-dimensional structure of a particularly diminutive CRISPR-Cas13 system, which could be crucial for modifying RNA.

The research, led in part by Yang Gao, an assistant professor of biosciences, centers on the CRISPR-Cas13bt3 system. Remarkably, while most molecules in this family contain around 1200 amino acids, this system has only about 700. This compact size offers the potential for better access and delivery to editing sites, Gao highlighted.

While many are familiar with the DNA-targeting capabilities of Cas9-related CRISPR systems, the Cas13 systems target RNA, the intermediary molecule that transforms DNA-encoded genetic data into a blueprint for protein creation. This RNA-targeting ability holds promise for combating RNA viruses.

To truly understand this system, Gao's lab decided to view it in 3D. Using a cryo-electron microscope, they intricately mapped the structure of the CRISPR tool. What they discovered was an unexpected difference in the mechanism used by this tool compared to other proteins in the Cas13 family.

This system, Gao explained, differs from its counterparts, “Other proteins in this family have two domains that are initially separated and, after the system is activated, they come together—kind of like the arms of a scissor—and perform a cut. This system is totally different: The scissor is already there, but it needs to hook onto the RNA strand at the right target site. To do this, it uses a binding element on these two unique loops that connect the different parts of the protein together.”

Highlighting the challenges faced during the research, Xiangyu Deng, a postdoc in the Gao lab, said they had to stabilize the protein and RNA complex to map it. After this, researchers from the lab of chemical engineer Xue Sherry Gao took the reins, refining the system for better precision by testing it in living cells.

Sherry Gao expressed enthusiasm about the project, noting, “We found that in cell cultures these systems were able to hone in on a target much easier. What is really remarkable about this work is that the detailed structural biology insights enabled a rational determination of the engineering efforts needed to improve the tool’s specificity while still maintaining high on-target RNA editing activity.”

Conclusive tests by Emmanuel Osikpa, a research assistant in the Xue Gao lab, showed that the engineered Cas13bt3 surpassed the original system's performance, emphasizing the potential of a targeted structural approach over broader, more expensive methods.