Structural and functional relevance of the DUF4352 domain in antiviral immunity and physiology of mycobacteria

Encounters between bacteria and bacteriophages have led to the evolution of phage and counter-defense arsenals, respectively. Multicopy phage resistance protein, Mpr, in mycobacteria is one such molecule providing resistance against D29 mycobacteriophage, probably by viral DNA degradation. Here, we demonstrate that the DUF4352 domain of Mpr (MprDUF4352) has viral origin, exhibits A/GTP hydrolysis, and synthesizes an unusual guanosine nucleotide, ppGp. The sequence and structure of MprDUF4352 are found to be conserved, and it shows compensatory effects when replaced in Mpr with phage-encoded hypothetical proteins harboring the DUF4352 domain. MprDUF4352 provides a structural framework and facilitates Mpr oligomerization, which is sensitive to GDP concentration. Oligomerized Mpr in the cell membrane cleaves mycobacteriophage genomic DNA, rendering the phage non-viable. As a counter-defense, D29 mutates Gp32 (minor tail protein), and escapes bacterial immunity. In conclusion, we present evidence that the host bacterium has repurposed a phage-encoded DUF4352 to orchestrate a non-abortive host phage defense.