Mechanism by which DNA ligase works How does it act on the a

Mechanism by which DNA ligase works? How does it act on the a DNA vector and the eukaryotic chromosomal DNA?

Solution

Answer :

Ligases catalyze the formation of phosphodiester bond between the 3’ OH and 5’ phosphate groups. DNA ligases are vital enzymes required for important cellular processes such as DNA replication, repair of damaged DNA and recombination. The enzyme mediates the formation of phosphodiester bonds between adjacent 3\'-OH and 5\'-phosphate termini, thereby joining the nicks in double stranded DNA. Ligases can be classified into two groups depending on their requirement for ATP or NAD+ as the cofactor. All eukaryotic and virally encoded enzymes are ATP-dependent, whereas most prokaryotic enzymes require NAD⁺ for their activity.

Mechanism – ATP donates its activated AMP unit to ligase to form a covalent enzyme – AMP complex in which AMP is linked to epsilon amino group of lysine residue of the enzyme through phosphoamide bond. The activated AMP moiety is then transferred from the lysine residue to the phosphate group at the 5 terminus of a DNA chain forming a DNA – adenylate complex. The final step is a nucleophilic attack by the 3’ OH group on this activated phosphorus atom.