Molecular mechanisms of CBASS phospholipase effector CapV mediated membrane disruption

Area of Science:

• Bacteriology
• Molecular Biology
• Structural Biology

Background:

• Cyclic oligonucleotide-based antiphage signaling systems (CBASS) are crucial bacterial defense mechanisms.
• These systems employ cyclic nucleotide-activated effectors to induce host cell death, primarily through membrane disruption.
• Patatin-like phospholipase CapV is a key effector in many CBASS pathways.

Purpose of the Study:

• To elucidate the mechanism by which CapV, a CBASS effector, induces membrane disruption and cell death.
• To understand the structural and conformational changes of CapV upon activation by the cyclic dinucleotide 3'3'-cGAMP.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structure of apo-CapV and its complexes.
• Biochemical assays were employed to study CapV's enzymatic activity and membrane binding properties.
• Cell-based assays were utilized to observe CapV's localization and effect on bacterial membranes.

Main Results:

• Apo-CapV exists in inactive dimeric and tetrameric states with an occluded phospholipid-binding pocket.
• 3'3'-cGAMP binding induces CapV filamentation, enhancing electrostatic membrane interactions and opening the active site.
• Activated CapV cleaves membrane phospholipids at the cell pole, leading to polarized membrane disruption and bacterial death.

Conclusions:

• CapV activation is filament-dependent, involving conformational changes triggered by 3'3'-cGAMP binding.
• This mechanism highlights a novel phospholipase-mediated membrane disruption strategy in bacterial antiviral immunity.
• The findings provide insights into the molecular basis of CBASS function and bacterial defense.