Structural insights into caspase ADPR deacylization catalyzed by a bacterial effector and host calmodulin

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Programmed cell death and caspases are vital for innate immunity against pathogens.
• Bacterial pathogens often inhibit host cell death as a virulence strategy.
• CopC effectors use calmodulin (CaM) to inactivate caspases via arginine ADPR deacylization.

Purpose of the Study:

• To elucidate the molecular mechanism of CopC-catalyzed arginine ADPR deacylization.
• To understand the binding and catalytic mechanisms of CopC with its co-factor CaM and substrate caspase-3.

Main Methods:

• Determined successive cryo-electron microscopy (cryo-EM) structures of the CaM-CopC-caspase-3 ternary complex.
• Captured pre-reaction, transition, and post-reaction states of the enzymatic process.
• Validated findings through in vitro mutagenesis and in vivo animal infection models.

Main Results:

• Elucidated a multistep enzymatic mechanism for CopC-catalyzed ADPR deacylization.
• Provided structural insights into the catalytic and co-factor/substrate binding of CopC.
• Observed the detachment of modified caspase-3 from CopC post-reaction.

Conclusions:

• Established a structural framework for understanding arginine ADPR deacylization by CopC family effectors.
• Demonstrated the role of CopC in bacterial virulence by inhibiting host cell death.
• Highlighted the importance of structural studies in deciphering enzyme mechanisms.