The Oligonucleotide/oligosaccharide binding (OB)-fold domain of kDNA ligase-like ATP-dependent DNA ligases is a DNA-binding module that is part of the catalytic core unit.
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. ATP-dependent ligases are present in many organisms such as viruses, bacteriohages, eukarya, archaea and bacteria. The mitochondrial DNA of parasitic protozoan is highly unusual. It is termed the kinetoplast DNA (kDNA) and consists of circular DNA molecules (maxicircles) and several thousand smaller circular molecules (minicircles). This group is composed of kDNA ligase, Chlorella virus DNA ligase, and similar proteins. kDNA ligase and Chlorella virus DNA ligase are the smallest known ATP-dependent ligases. They are involved in DNA replication or repair. ATP dependent DNA ligases have a highly modular architecture consisting of a unique arrangement of two or more discrete domains. The adenylation and oligonucleotide/oligosaccharide binding (OB)-fold domains comprise a catalytic core unit that is common to most members of the ATP-dependent DNA ligase family. The catalytic core unit contains six conserved sequence motifs (I, III, IIIa, IV, V and VI) that define this family of related nucleotidyltransferases. The OB-fold domain contacts the nicked DNA substrate and is required for the ATP-dependent DNA ligase nucleotidylation step. The RxDK motif (motif VI), which is essential for ATP hydrolysis, is located in the OB-fold domain.