Csx28 is a membrane pore that enhances CRISPR-Cas13b-dependent antiphage defense

Science. 2023 Apr 28;380(6643):410-415. doi: 10.1126/science.abm1184. Epub 2023 Apr 27.

Abstract

Type VI CRISPR-Cas systems use RNA-guided ribonuclease (RNase) Cas13 to defend bacteria against viruses, and some of these systems encode putative membrane proteins that have unclear roles in Cas13-mediated defense. We show that Csx28, of type VI-B2 systems, is a transmembrane protein that assists to slow cellular metabolism upon viral infection, increasing antiviral defense. High-resolution cryo-electron microscopy reveals that Csx28 forms an octameric pore-like structure. These Csx28 pores localize to the inner membrane in vivo. Csx28's antiviral activity in vivo requires sequence-specific cleavage of viral messenger RNAs by Cas13b, which subsequently results in membrane depolarization, slowed metabolism, and inhibition of sustained viral infection. Our work suggests a mechanism by which Csx28 acts as a downstream, Cas13b-dependent effector protein that uses membrane perturbation as an antiviral defense strategy.

MeSH terms

  • Bacterial Proteins* / chemistry
  • Bacterial Proteins* / metabolism
  • Bacteriophage lambda / metabolism
  • Bacteriophages* / metabolism
  • CRISPR-Associated Proteins* / chemistry
  • CRISPR-Associated Proteins* / metabolism
  • CRISPR-Cas Systems*
  • Cryoelectron Microscopy
  • Endodeoxyribonucleases* / chemistry
  • Endodeoxyribonucleases* / metabolism
  • Escherichia coli / enzymology
  • Escherichia coli / virology
  • Membrane Proteins / metabolism
  • Prevotella* / enzymology
  • Prevotella* / virology
  • RNA Cleavage*
  • RNA, Viral* / metabolism

Substances

  • Membrane Proteins
  • RNA, Viral
  • Bacterial Proteins
  • Endodeoxyribonucleases
  • CRISPR-Associated Proteins

Supplementary concepts

  • Prevotella buccae