Biochemical and Mechanistic Characterization of the DNA-dependent Poly(ADP-ribose) Polymerase, MoPARP1, in Magnaporthe oryzae
Poly(ADP-ribose) polymerases (PARPs) are important regulators of DNA repair and cellular stress responses in eukaryotes. Although mammalian PARPs have been extensively characterized, comparatively little is known about PARPs in pathogenic filamentous fungi. Here, we define biochemical features of MoPARP1 from the plant-pathogenic fungus Magnaporthe oryzae. Mutation of the conserved catalytic glutamate E714 abolished detectable PARylation activity, whereas PAR generated by MoPARP1 was hydrolyzed by human PARG, suggesting synthesis of polymeric ADP-ribose. Several mammalian PARP inhibitors were effective against MoPARP1 in vitro, consistent with conservation of the catalytic inhibitor-binding pocket. DNA substrates containing 5' phosphate enhanced MoPARP1 catalytic activity, while both wild-type MoPARP1 and the catalytically inactive MoPARP1 E714A bound diverse DNA substrates. Quantitative analyses revealed that structurally distinct DNA substrates exhibit similar apparent binding affinities yet yield markedly different catalytic outputs, suggesting that DNA engagement alone does not determine productive PAR synthesis. MoPARP1 lacks the canonical N-terminal zinc-finger domains of human PARP1 and instead depends on its WGR-containing region for DNA association. Domain truncation analyses showed the BRCT-WGR region supports high-affinity DNA binding, whereas the WGR-PARP region retains catalytic competence despite weaker DNA affinity. Together, these findings establish a mechanistic framework for DNA-dependent PARylation in a filamentous fungal plant pathogen.