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1.A.133.  The Bacterial Csx28 Pore-forming (Csx28) Family

Csx28, of type VI-B2CRISPER-Cas systems, is a transmembrane protein that assists to slow cellular metabolism upon viral infection, increasing antiviral defense. High-resolution cryo-electron microscopy revealed that Csx28 forms an octameric pore-like structure in the inner bacterial membrane in vivo (VanderWal et al. 2023). 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. This suggests a mechanism by which Csx28 acts as a downstream, Cas13b-dependent effector protein that uses membrane perturbation as an antiviral defense strategy (VanderWal et al. 2023).

 

References associated with 1.A.133 family:

VanderWal, A.R., J.U. Park, B. Polevoda, J.K. Nicosia, A.M. Molina Vargas, E.H. Kellogg, and M.R. O'Connell. (2023). Csx28 is a membrane pore that enhances CRISPR-Cas13b-dependent antiphage defense. Science 380: 410-415. 37104586