5tt6

Publication Abstract from PubMed

Polynucleotide ligases comprise a ubiquitous superfamily of nucleic acid repair enzymes that join 3'-OH and 5'-PO4 DNA or RNA ends. Ligases react with ATP or NAD+ and a divalent cation cofactor to form a covalent enzyme-(lysine-Nzeta)-adenylate intermediate. Here, we report crystal structures of the founding members of the ATP-dependent RNA ligase family (T4 RNA ligase 1; Rnl1) and the NAD+-dependent DNA ligase family (Escherichia coli LigA), captured as their respective Michaelis complexes, which illuminate distinctive catalytic mechanisms of the lysine adenylylation reaction. The 2.2-A Rnl1*ATP*(Mg2+)2 structure highlights a two-metal mechanism, whereby: a ligase-bound "catalytic" Mg2+(H2O)5 coordination complex lowers the pKa of the lysine nucleophile and stabilizes the transition state of the ATP alpha phosphate; a second octahedral Mg2+ coordination complex bridges the beta and gamma phosphates; and protein elements unique to Rnl1 engage the gamma phosphate and associated metal complex and orient the pyrophosphate leaving group for in-line catalysis. By contrast, the 1.55-A LigA*NAD+*Mg2+ structure reveals a one-metal mechanism in which a ligase-bound Mg2+(H2O)5 complex lowers the lysine pKa and engages the NAD+ alpha phosphate, but the beta phosphate and the nicotinamide nucleoside of the nicotinamide mononucleotide (NMN) leaving group are oriented solely via atomic interactions with protein elements that are unique to the LigA clade. The two-metal versus one-metal dichotomy demarcates a branchpoint in ligase evolution and favors LigA as an antibacterial drug target.

Two-metal versus one-metal mechanisms of lysine adenylylation by ATP-dependent and NAD+-dependent polynucleotide ligases.,Unciuleac MC, Goldgur Y, Shuman S Proc Natl Acad Sci U S A. 2017 Feb 21. pii: 201619220. doi:, 10.1073/pnas.1619220114. PMID:28223499^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.