Application of bacterial antiviral defense CRISPR-Cas system as a genome editing tool and recent developments in bioinformatics tools, advances in genomic sequencing techniques and experimental progress have sparked a breakthrough in the study of bacterial antiviral defense systems, resulting in the identification of more than 100 new prokaryotic antiviral defense systems [1]. Despite significant progress, many of these newly found systems remain poorly understood, and further research continues to uncover novel features of known defense systems.
Thoeris is an abortive bacterial antiviral defense system that can be classified into 4 types. The system consists of two genes – thsA and thsB. ThsB protein contains Toll/interleukin-1 receptor (TIR) domain in all Thoeris types while ThsA proteins are different [2-4]. Thoeris mechanism of action is based on intracellular signaling: the ThsB protein detects phage infection and produces a signaling molecule, which is recognized by the effector protein ThsA, leading to its activation. Upon bacteriophage infection, Thoeris type I ThsB produces a signaling molecule 1’-3’gcADPR, which is bound by ThsA SLOG domain [5,6]. Activated ThsA forms helical filaments, enabling SIR2 NAD\(^{+}\) hydrolase activity and resulting in NAD\(^{+}\) depletion and host cell death [7]. Type II Thoeris active ThsB produces a different signaling molecule His-ADPR, which is bound by ThsA Macro domain, followed by ThsA oligomerization and presumably cell membrane perturbation [8]. Type IV Thoeris active ThsB synthesizes N7-cADPR, which activates a caspase-like effector that nonspecifically degrades intracellular and potentially bacteriophage proteins [4]. Type III Thoeris mechanism is unknown [3].
Here, we characterize a new Thoeris protein by biochemical analyses. We also performed in vivo experiments to study the impact of this protein for phage defense. These results will provide a deeper understanding of the bacterial immunity.