Poster abstracts
Poster number 17 submitted by Anthony Rish
Machine-learning structure guided characterization of a novel bacterial anti-phage system
Anthony Rish (Ohio State Biochemistry Program), Elizabeth Fosuah (Ohio State Biochemistry Program), Tianmin Fu (Comprehensive Cancer Center)
Abstract:
The constant arms race between viruses and their hosts led to the evolution of antiviral defenses. Recent studies have revealed that bacteria developed diverse anti-phage defense systems such as restriction-modification (R-M), CRISPR-Cas, and abortive infection systems. Mechanistic characterization of these systems has revolutionized biomedical research with R-M becoming an essential tool for molecular cloning and CRISPR-Cas having completely changed the genome editing field. Here we structurally and functionally characterized a novel bacterial anti-phage defense system, HerA_DUF4297, via machine learning and structure-guided biochemical analysis. We have multiple cryo-EM density maps that identify HerA, a classical ATPase DNA helicase homolog, as a cyclic ring-like hexamer, bound to a larger 12-mer DUF assembly. DUF consists of two previously uncharacterized domains, which we have attributed to an N-terminal nuclease domain and a C-terminal universal fold for oligomerization domain. When in complex with HerA, DUF has divalent cation-dependent non-specific nuclease activity for dsDNA substrates. Interestingly, HerA has enhanced ATPase activity when bound to DUF, and at physiological concentrations, ATP inhibits the nuclease activity of DUF. There is a decoupling of inhibition through ATP binding and ATP hydrolysis since non-hydrolyzable analogs of ATP are sufficient for nuclease inhibition. Since this HerA homolog has no detectable strand displacement helicase activity, HerA likely acts as a molecular switch to regulate DUF. Upon phage infection and initial propagation within the cell, local ATP concentrations may drop enough to lose inhibitory activity, allowing DUF to digest both host and viral nucleic acids, leading to abortive infection to contain the spread of phages. Our work sets a foundation for characterizing the over 4,000 known DUF proteins whose biological function and potential biomedical or therapeutic application remain unknown.
Keywords: Cryo-EM, Phage defense, Immunology