Structure of the Saccharolobus solfataricus type III-D CRISPR effector

Area of Science:

• Molecular Biology
• Microbiology
• Structural Biology

Background:

• CRISPR-Cas systems provide adaptive immunity in prokaryotes, with six main types.
• Type III CRISPR-Cas systems, defined by the Cas10 subunit, are complex and diverse.
• While Type II systems dominate biotechnology, Type III systems are emerging as RNA-targeting tools.

Purpose of the Study:

• To determine the cryo-electron microscopy (cryo-EM) structure of the Type III-D Csm complex from Saccharolobus solfataricus (SsoCsm).
• To elucidate the complex organization, subunit interactions, and guide RNA binding of the SsoCsm complex.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structure of the SsoCsm complex.
• Bioinformatic analysis and biochemical assays were employed to understand its function.

Main Results:

• The cryo-EM structure of the SsoCsm complex, a large Type III-D CRISPR effector, was resolved.
• The structure details the intricate organization, subunit connectivity, and interactions with CRISPR RNA (crRNA) and target RNA.
• Activation of the Cas10 subunit upon target binding was observed.

Conclusions:

• The SsoCsm complex represents one of the largest known CRISPR effector complexes.
• Understanding its structure provides insights into the mechanism of RNA-guided DNA/RNA targeting and antiviral defense in Type III systems.
• This work supports the development of Type III CRISPR-Cas systems for biotechnological applications.