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Crystal Structure of the Ligase Domain from M. tuberculosis LigD at 2.4A
Structural highlights
FunctionLIGD_MYCTU With Ku forms a non-homologous end joining (NHEJ) repair enzyme which repairs DNA double-strand breaks (DSB) with reduced fidelity. Recognizes, processes and reseals DSBs, including repairs on incompatible DSB which require 3'-resection, gap filling and ligation. Anneals the 3' overhanging strands from opposing breaks to form a gapped intermediate, which then can be extended in trans by using the termini as primers for extension of the annealed break. Binds to the recessed 5'-phosphate moiety of the downstream DNA strand forming a stable synaptic complex even when the 3'-protruding ends of the template DNA strands are not complementary. Has numerous activities; gap filling copies the template strand, and prefers a 5'-phosphate in the gap and rNTPS (PubMed:17174332, PubMed:17947582), DNA-directed DNA or RNA polymerase on 5'-overhangs, terminal transferase (extending ssDNA or blunt dsDNA in a non-templated fashion, preferentially with rNTPs), DNA-dependent RNA primase (synthesizes short RNAs on unprimed closed ssDNA) and 3'- to 5'-exonuclease on ssDNA (PubMed:15499016). Isolated Pol domain (and presumably the holoenzyme) is able to form complexes between 2 noncompatible protruding 3'-ends DNA ends via microhomologous DNA strands, in a end-bridging function to which it adds a templated nucleotide (PubMed:17947582). Minimal primer length is 2 nucleotides (PubMed:21255731).[1] [2] [3] [4] The preference of the polymerase domain for rNTPs over dNTPs may be advantageous in dormant cells, where the dNTP pool is limiting. In conjunction with endogenous or Mycobacterium phage Omega Ku (AC Q853W0) can reconstitute NHEJ in Saccharomyces cerevisiae. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedDNA ligase D (LigD) is a large polyfunctional enzyme involved in nonhomologous end-joining (NHEJ) in mycobacteria. LigD consists of a C-terminal ATP-dependent ligase domain fused to upstream polymerase and phosphoesterase modules. Here we report the 2.4 angstroms crystal structure of the ligase domain of Mycobacterium LigD, captured as the covalent ligase-AMP intermediate with a divalent metal in the active site. A chloride anion on the protein surface coordinated by the ribose 3'-OH and caged by arginine and lysine side chains is a putative mimetic of the 5'-phosphate at a DNA nick. Structure-guided mutational analysis revealed distinct requirements for the adenylylation and end-sealing reactions catalyzed by LigD. We found that a mutation of Mycobacterium LigD that ablates only ligase activity results in decreased fidelity of NHEJ in vivo and a strong bias of mutagenic events toward deletions instead of insertions at the sealed DNA ends. This phenotype contrasts with the increased fidelity of double-strand break repair in deltaligD cells or in a strain in which only the polymerase function of LigD is defective. We surmise that the signature error-prone quality of bacterial NHEJ in vivo arises from a dynamic balance between the end-remodeling and end-sealing steps. Crystal structure and nonhomologous end-joining function of the ligase component of Mycobacterium DNA ligase D.,Akey D, Martins A, Aniukwu J, Glickman MS, Shuman S, Berger JM J Biol Chem. 2006 May 12;281(19):13412-23. Epub 2006 Feb 13. PMID:16476729[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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