IISER MOHALI

Abstract:
Nucleoside triphosphate (NTP)-dependent restriction enzymes are one of the most common bacterial defense systems that prevent the entry of foreign DNA and protect bacteria from phage infection. These enzymes regulate horizontal gene transfer and acquisition of genetic elements harbouring pathogenic islands and antibiotic resistance genes. Biochemical and structural studies carried out on ATP-dependent restriction enzymes in my laboratory are unravelling their mechanism of action. These enzymes have a nuclease coupled to an ATPase belonging to the Superfamily 2 helicases. The ATPase facilitates directional movement of the enzyme on the DNA, called translocation, or long range diffusion along the DNA. We find that the ATP-dependent DNA cleavage is distinct from the known modes of DNA cleavage by other nucleases. Double strand DNA cleavage by nucleases can be broadly classified as i) endonucleolytic resulting in hydrolysis of a pair of spatially close phosphodiester bonds on the two strands within the duplex; ii) exonucleolytic resulting in cleavage of a strand from the duplex ends. Our studies of certain classes of these enzymes have revealed that they make multiple nicks on the DNA in between two of their target sites. Nicks at multiple locations on the DNA away from the target site are made possible by the translocase activity of the ATPase that propels the nuclease on the DNA. The nicks result in the DNA being shredded between the two target sequences. I will describe this unique mode of DNA cleavage, and its possible physiological relevance.