January 22, 2021

The O'Brien lab publishes an article in Nucleic Acids Research

LIG1 syndrome mutations remodel a cooperative network of ligand binding interactions to compromise ligation efficiency

Human DNA ligase I (LIG1) is the main replicative ligase and it also seals DNA breaks to complete DNA repair and recombination pathways. Immune compromised patients harbor hypomorphic LIG1 alleles encoding substitutions of conserved arginine residues, R771W and R641L, that compromise LIG1 activity through poorly defined mechanisms. To understand the molecular basis of LIG1 syndrome mutations, researchers in the O'Brien lab and their collaborators at the NIEHS and the Icahn School of Medicine at Mount Sinai determined high resolution X-ray structures and performed systematic biochemical characterization of LIG1 mutants using steady-state and pre-steady state kinetic approaches. Their results, which have been published in the journal Nucleic Acids Research, unveil a cooperative network of plastic DNA-LIG1 interactions that connect DNA substrate engagement with productive binding of Mg2+ cofactors for catalysis. LIG1 syndrome mutations destabilize this network, compromising Mg2+ binding affinity, decreasing ligation efficiency, and leading to elevated abortive ligation that may underlie the disease pathology. These findings provide novel insights into the fundamental mechanism by which DNA ligases engage with a nicked DNA substrate, and they suggest that disease pathology of LIG1 syndrome could be modulated by Mg2+ levels.

Structural morph between WT and R641L mutant LIG1 conformation. The R641L loop (pink) transits from a DNA engaged state (start and end of movie) to the mutant state. DNA binding side chains K642, R643 and K644 (pink sticks with surfaces) bind DNA in the WT enzyme, but they disengage with DNA in the mutant structure. Morphing performed in Pymol.