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).