Craspase is a CRISPR RNA-guided, RNA-activated protease.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• The CRISPR-Cas type III-E system utilizes the effector complex gRAMP/Cas7-11.
• This complex associates with TPR-CHAT/Csx29 to form the Craspase enzyme.
• Craspase functions as a CRISPR-guided caspase with RNA-targeting and protease activities.

Purpose of the Study:

• To elucidate the mechanisms of target RNA cleavage and protease activation in Craspase.
• To identify the endogenous protein substrate of Craspase.
• To understand the self-regulatory capacity of the Craspase system.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to capture structural snapshots of Craspase.
• Biochemical assays to study RNA binding, cleavage, and protease activity.
• Identification and characterization of Craspase's protein substrate.

Main Results:

• Target-guide RNA pairing in the 5' region displaces a gating loop, initiating conformational changes.
• These changes allosterically activate the protease catalytic dyad and create a substrate-binding pocket.
• Csx30 was identified as the endogenous substrate, proteolyzed site-specifically by activated Craspase.
• Protease activity is inhibited upon target RNA cleavage by gRAMP and not activated by specific RNA sequences.

Conclusions:

• Craspase is a novel RNA-activated protease with intrinsic self-regulatory mechanisms.
• The system demonstrates precise control over protease activity, linked to target RNA recognition and cleavage.
• This research provides structural and mechanistic insights into CRISPR-Cas system diversification.