DNSligázok

DNSligázok, also known as DNA ligases, are enzymes that catalyze the formation of phosphodiester bonds between adjacent nucleotides in the DNA sugar-phosphate backbone, sealing nicks in double-stranded DNA. They are essential for DNA replication, repair, and recombination, and operate across prokaryotic and eukaryotic organisms. In bacteria, ligases typically use nicotinamide adenine dinucleotide (NAD+) as a cofactor, whereas in eukaryotes and most archaea, ligases are ATP-dependent.

DNA ligases employ a two-step mechanism. First, the enzyme is adenylated, forming an enzyme–AMP intermediate. The AMP is then transferred to the 5' phosphate of the DNA, creating a DNA–adenylate intermediate. The 3' hydroxyl of the adjacent nucleotide attacks this intermediate, forming the new phosphodiester bond and releasing AMP. The reaction often requires divalent cations such as Mg2+ (and sometimes Mn2+). Structural diversity exists, with multi-domain architectures tailored to specific pathways and substrates.

In eukaryotes, distinct ligases fulfill specialized cellular roles. DNA ligase I primarily participates in lagging-strand processing during replication and in base excision repair; DNA ligase III operates with XRCC1 in base excision and single-strand break repair; DNA ligase IV functions in non-homologous end joining (NHEJ) alongside XRCC4 and XLF. Bacterial ligases are primarily involved in replication and repair, and some viruses encode their own ligases for genome maintenance.

DNSligázok are widely used in molecular biology as cloning tools to join DNA fragments, enabling plasmid construction, gene assembly, and various genetic engineering techniques. Enzyme choice may depend on cofactor requirements (NAD+-dependent vs ATP-dependent) and the nature of the DNA ends being joined.