Adenylation domain of Mycobacterium tuberculosis LigD and LigC-like ATP-dependent DNA ligases
Bacterial DNA ligases are divided into two broad classes: NAD-dependent and ATP-dependent. All bacterial species have a NAD-dependent DNA ligase (LigA). Some bacterial genomes contain multiple genes for DNA ligases that are predicted to use ATP as their cofactor, including Mycobacterium tuberculosis LigB, LigC, and LigD. This group is composed of ATP-dependent DNA ligases similar to Mycobacterium tuberculosis LigC. ATP-dependent polynucleotide ligases catalyze phosphodiester bond formation using nicked nucleic acid substrates with the high energy nucleotide of ATP as a cofactor in a three step reaction mechanism. DNA ligases play a vital role in the diverse processes of DNA replication, recombination and repair. Members of this group contain adenylation and C-terminal oligonucleotide/oligosaccharide binding (OB)-fold domains, comprising a catalytic core unit that is common to all members of the ATP-dependent DNA ligase family. The adenylation domain binds ATP and contains many of the active-site residues. The common catalytic core unit comprises six conserved sequence motifs (I, III, IIIa, IV, V and VI) that define this family of related nucleotidyltransferases. LigD consists of a central ATP-dependent DNA ligase catalytic core unit fused to a C-terminal polymerase domain and an N-terminal 3'-phosphoesterase (PE) module. LigD catalyzes the end-healing and end-sealing steps during non-homologous end joining.
Comment:based on similarity to other members of the family
Comment:Sealing a nick in DNA requires three catalytic steps: first, enzyme adenylation is accomplished using ATP resulting in an AMP-linkage to the enzyme; second, the AMP is transferred to the 5' phosphate at the site of a nick; and third, phosphoryl transfer and sealing the nick DNA.
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