Our genomic DNA is constantly modified and damaged by endogenous and environmental agents, from base deamination, oxidation and large adduct formaion to double-strand breaks. Endonuclease V (EndoV) cleaves the second phosphodiester bond 3¢ to a deaminated adenosine (inosine). Although highly conserved, EndoV homologs change substrate preference from DNA in bacteria to RNA in eukaryotes. We have characterized EndoV from six different species and determined crystal structures of human EndoV and three EndoV homologs from bacteria to mammals in complex with inosine-containing DNA/RNA hybrid or dsRNA. Inosine recognition is conserved, but changes in several connecting loops in eukaryotic EndoV confer recognition of 3 ribonucleotides upstream and 6-7 bp of dsRNA downstream of the cleavage site, while bacterial EndoV binds only 2-3 nucleotides flanking the scissile phosphate. Using time-resolved crystallography, we find that in addition to the two canonical metal ions in the active site, a third Me<sup>2+</sup> that coordinates the nucleophilic water is necessary for the cleavage reaction. Comparison of EndoV with its homologs RNase H1 and Argonaute reveals the principles by which these enzymes recognize RNA versus DNA and molecular evolution of nucleic-acid enzymes.

DNA repair and RNA regulation in multiple dimensions

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.