DNA ligase (LigD) is an enzyme which repairs single-stranded breaks in a double-stranded DNA. LigD is activated , in a species-dependent manner, by hydrolysis of ATP or NAD+. Mammalian LigD I ligates the nascent DNA of the lagging strand; LigD III complexes with XRCC1 in the process of nucleotide excision repair; LigD IV complexes with XRCC4 and catalyzes the last step in the non-homologous DNA end joining.LigD contains several domains: adenylation domain; DNA-binding domain and the ca. 100 amino acid long BRCT motif.
Known disease associated with this structure: DNA ligase I deficiency OMIM:[126391]
The expression of DNA ligase I has been directly linked to cancer in humans. The enzyme is found most in proliferating cells and much less often in nondividing cells. In particular, in malignant tumors, the DNA ligase I enzyme was expressed much more compared to the DNA ligase I enzyme in normal tissues and their peripheral lymphocytes. Further experimentation showed that tumor cell growth rate was successfully decreased when antisense oligonucleotides targeting the mRNA of DNA ligase I were present. This suggests that DNA ligase I could be a good target for new anticancer studies.
A specific point mutation (46BR in the mouse Lig1 gene) in DNA ligase I has also been linked as a cause for genome instability and cancer in humans. One possible reason for this is the accumulation of DNA fragments that are no longer ligated by the mutant DNA ligase I enzyme.
1x9n – hLigD I + DNA + AMP + CMP – human 2od8 – LigD I residues 32-53 + PCNA
Mammalian LigD III
3l2p – hLigD III residues 257-833 + DNA 1uw0 - hLigD III zinc-finger domain residues 1-117 – NMR 1imo, 1in1 - hLigD III BRCTdomain – NMR 3pc7 - hLigD III BRCTdomain 3pc8 - hLigD III BRCTdomain (mutant) + XRCC1 3qvg - hLigD III BRCTdomain + XRCC1
Mammalian LigD IV
3ii6, 1ik9 – hLigD IV C-terminal BRCT domains + DNA repair protein XRCC4 2e2w - hLigD IV BRCT domain - NMR 1z56 – LigD IV + ligase interacting factor 1 - yeast 3vnn - hLigD IV adenylation domain 4hto - hLigD IV DNA-binding domain 4htp - hLigD IV DNA-binding domain + artemis protein peptide
REFERENCES
Elevated expression of DNA ligase I in human cancers., Sun DY, Urrabaz R, Nguyen M, Marty J, Stringer S, Cruz E, Medina-Gundrum L, Weitman S., Clinical Cancer Research. 2001; 7(12):4143-4148. Replication failure, genome instability, and increased cancer susceptibility in mice with a point mutation in the DNA ligase I gene., Harrison C, Ketchen AM, Redhead NJ, O'Sullivan MJ, Melton DW., Cancer Research. 2002; 62(14):4065-4074.