Effector-mediated membrane disruption controls cell death in CBASS antiphage defense

Area of Science:

• Microbiology
• Molecular Biology
• Bacteriology

Background:

• Cyclic oligonucleotide-based antiphage signaling systems (CBASS) are crucial bacterial defense mechanisms against phage infection.
• CBASS operons utilize various effector proteins to halt phage replication.
• Transmembrane (TM) effectors represent a significant but poorly understood class within CBASS systems.

Purpose of the Study:

• To identify and characterize a widespread class of CBASS transmembrane effector proteins.
• To elucidate the mechanism by which these TM effectors inhibit phage propagation.
• To define the role of inner membrane disruption in bacterial antiviral defense.

Main Methods:

• Crystal structure determination of the Yersinia TM effector Cap15.
• Analysis of Cap15's oligomerization and relocalization upon activation.
• Functional screening of CBASS TM effectors to identify active families.
• Assays to assess inner membrane integrity and cell viability.

Main Results:

• Discovery of a conserved class of CBASS TM effectors that disrupt bacterial membranes.
• Structural analysis revealed Cap15 forms an oligomeric complex upon binding cyclic dinucleotides.
• Activated Cap15 induces specific rupture of the bacterial inner membrane.
• Inner membrane disruption is a common mechanism employed by distinct CBASS TM effector families.

Conclusions:

• CBASS transmembrane effectors are a prominent class of bacterial antiviral proteins.
• These effectors function by directly disrupting the inner membrane, leading to cell death (abortive infection).
• Inner membrane disruption represents a widespread and effective bacterial strategy against phage predation.