The two-component nuclease-active KELShedu system confers broad antiphage activity via abortive infection

Bacteriophages and bacteria engage in a continuous evolutionary arms race, driving the development of intricate bacterial defense systems such as CRISPR-Cas, BREX (Bacteriophage Exclusion), Gabija, and Shedu. Here, we characterize a two-component KELShedu system in <i>Escherichia coli</i> that confers resistance to phages via abortive infection. The KELShedu system comprises KELA, a double-stranded DNA-binding protein, and KELB, a metal ion-dependent nuclease harboring the DUF4263 domain. In addition, we find that physiological levels of nucleotide triphosphates (NTPs) inhibit the DNA cleavage activity of the KELShedu system, suggesting that KELShedu's activation depends on reduced intracellular NTP levels during phage invasion. Our research demonstrates that the KELShedu system responds to nucleotide depletion triggered by phage replication, leading to nonspecific degradation of cellular DNA and ultimately inducing abortive infection. These insights into the KELShedu system expand the repertoire of bacterial antiphage mechanisms and lay the groundwork for applications in microbial engineering and therapeutic development.