NAD+ -dependent DNA ligase: A novel target waiting for the right inhibitor

Abstract

DNA ligases (EC.6.5.1.1) are key enzymes that catalyze the formation of phosphodiester bonds at single stranded or double stranded breaks between adjacent 5’phosphoryl and 3’ hydroxyl groups of DNA. These enzymes are important for survival because these are involved in major cellular processes like DNA replication/repair and recombination. DNA ligases can be classified into two groups on the basis of their cofactor specificities. NAD+ dependent DNA ligases are present in bacteria, some entomopox viruses and mimi virus while ATP -dependent DNA ligases are ubiquitous. NAD+ -dependent ligases have recently been drawing a lot of attention as novel targets with the potential to overcome current drug resistance issues. Currently a diverse range of inhibitors have been identified including several by our group. There are several issues to be addressed in the quest for optimized inhibitors of the enzyme. In the first part of the review we summarise current structural work on these enzymes. Subsequently we describe the currently available classes of inhibitors. We also address modalities to improve the specificity and potencies of new inhibitors which can be identified using protein structure based rational approaches. In conclusion, NAD+ -dependent ligases show great promise and represent a novel drug target whose time has come.