RNA targeting and cleavage by the type III-Dv CRISPR effector complex.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• CRISPR-Cas systems provide adaptive immunity in prokaryotes.
• Type III CRISPR-Cas effector complexes are known for RNA-guided RNA or DNA cleavage.
• The evolution from multi-protein to single-protein type III effectors is not fully understood.

Purpose of the Study:

• To determine the structures of the Synechocystis type III-Dv complex, an evolutionary intermediate.
• To elucidate the mechanism of RNA targeting and cleavage by this intermediate effector.
• To understand the evolutionary transition of type III CRISPR-Cas effector complexes.

Main Methods:

• X-ray crystallography to obtain pre- and post-cleavage structures.
• Biochemical assays to study RNA cleavage activity.
• Quantum/classical molecular dynamics simulations to analyze catalytic site dynamics.

Main Results:

• The structure reveals an unusual tethering arrangement of multi-subunit fusion proteins in the type III-Dv complex.
• A distinct mechanism for target RNA binding and initiation of cleavage was observed.
• The catalytic sites share similarities with ribozymes, suggesting a conserved catalytic mechanism.

Conclusions:

• The Synechocystis type III-Dv complex represents a key intermediate in the evolution of type III CRISPR-Cas effectors.
• The study provides detailed molecular insights into RNA recognition and self-cleavage.
• This work enhances our understanding of CRISPR-Cas system evolution and function.