:Crossover junction endodeoxyribonuclease

The Holliday junction is a structure that forms during genetic recombination, and links two double-stranded DNA molecules with a single-stranded crossover, which form during mitotic and meiotic recombination. Crossover junction endodeoxyribonucleases catalyze Holiday junction resolution, which is the formation of separate recombinant DNA molecules and chromosomal separation after the crossover event at the Holliday junction.{{cite journal | vauthors = Cañas C, Suzuki Y, Marchisone C, Carrasco B, Freire-Benéitez V, Takeyasu K, Alonso JC, Ayora S | title = Interaction of branch migration translocases with the Holliday junction-resolving enzyme and their implications in Holliday junction resolution | journal = The Journal of Biological Chemistry | volume = 289 | issue = 25 | pages = 17634–46 | date = June 2014 | pmid = 24770420 | pmc = 4067198 | doi = 10.1074/jbc.M114.552794 | doi-access = free }} Crossover junction endodeoxyribonucleases with Holliday Junction resolution function have been identified in all three domains of life - bacteria, archaea, and eukarya. RuvC in bacteria, CCE1 in Saccharomyces cerevisiae,{{cite journal | vauthors = Iwasaki H, Takahagi M, Shiba T, Nakata A, Shinagawa H | title = Escherichia coli RuvC protein is an endonuclease that resolves the Holliday structure | journal = The EMBO Journal | volume = 10 | issue = 13 | pages = 4381–9 | date = December 1991 | pmid = 1661673 | doi = 10.1002/j.1460-2075.1991.tb05016.x | pmc = 453191 }} and GEN1 in humans {{cite journal | vauthors = Ip SC, Rass U, Blanco MG, Flynn HR, Skehel JM, West SC | title = Identification of Holliday junction resolvases from humans and yeast | journal = Nature | volume = 456 | issue = 7220 | pages = 357–61 | date = November 2008 | pmid = 19020614 | doi = 10.1038/nature07470 | bibcode = 2008Natur.456..357I | s2cid = 4362699 }} are all crossover junction endodeoxyribonucleases that perform Holliday Junction resolution. Holliday junction resolution catalyzed by crossover junction endodeoxyribonuclease is shown in the figure below.

File:Resolvase function.png

Crossover junction endodeoxyribonucleases also play key roles in DNA repair. During cell growth and meiosis, DNA double-strand breaks (DSBs) often occur, and are usually repaired by homologous recombination.{{cite journal | vauthors = Agmon N, Yovel M, Harari Y, Liefshitz B, Kupiec M | title = The role of Holliday junction resolvases in the repair of spontaneous and induced DNA damage | journal = Nucleic Acids Research | volume = 39 | issue = 16 | pages = 7009–19 | date = September 2011 | pmid = 21609961 | pmc = 3167605 | doi = 10.1093/nar/gkr277 }} Because Crossover junction endodeoxyribonucleases perform Holliday Junction resolution, a crucial step of homologous recombination, they are therefore involved in repair of DSBs.

E. coli RuvC, a Crossover junction endodeoxyribonuclease, is a small protein of about 20 kD, and its active form is a dimer that requires and binds a magnesium ion [1]. RuvC is a 3-layer alpha-beta sandwich with a beta-sheet between 5 alpha-helices

. The enzyme contains two binding channels that contact the backbones of the Holliday junction over seven nucleotides.{{cite journal | vauthors = Lilley DM | title = Holliday junction-resolving enzymes-structures and mechanisms | journal = FEBS Letters | volume = 591 | issue = 8 | pages = 1073–1082 | date = April 2017 | pmid = 27990631 | doi = 10.1002/1873-3468.12529 | url = https://discovery.dundee.ac.uk/ws/files/11272660/Lilley_2016_FEBS_Letters_1_.pdf | doi-access = free }} A Holliday junction resolvase enzyme has also been identified in archaea in Pyrococcus furiosus cells - it is encoded by a gene called hjc and is composed of 123 amino acids {{cite journal | vauthors = Komori K, Sakae S, Shinagawa H, Morikawa K, Ishino Y | title = A Holliday junction resolvase from Pyrococcus furiosus: functional similarity to Escherichia coli RuvC provides evidence for conserved mechanism of homologous recombination in Bacteria, Eukarya, and Archaea | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 96 | issue = 16 | pages = 8873–8 | date = August 1999 | pmid = 10430863 | doi = 10.1073/pnas.96.16.8873 | bibcode = 1999PNAS...96.8873K | pmc = 17700 | doi-access = free }}

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A figure of Thermus thermophilus RuvC in complex with a Holliday junction is shown below.

[[File:4LD0.png|thumb|center|upright=2.0|Archaea crossover junction endodeoxyribonuclease in complex with Holliday Junction DNA. Generated with 4LD0.pdb.{{cite journal | vauthors = Górecka KM, Komorowska W, Nowotny M | title = Crystal structure of RuvC resolvase in complex with Holliday junction substrate | journal = Nucleic Acids Research | volume = 41 | issue = 21 | pages = 9945–55 | date = November 2013 | pmid = 23980027 | pmc = 3834835 | doi = 10.1093/nar/gkt769 }}

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These enzymes are highly selective for branched DNA, although induced fit occurs in the enzyme-substrate (resolvase-Holloday Junction) complex formation.{{cite journal | vauthors = Rass U, Compton SA, Matos J, Singleton MR, Ip SC, Blanco MG, Griffith JD, West SC | title = Mechanism of Holliday junction resolution by the human GEN1 protein | journal = Genes & Development | volume = 24 | issue = 14 | pages = 1559–69 | date = July 2010 | pmid = 20634321 | pmc = 2904945 | doi = 10.1101/gad.585310 }} Much remains unknown about the exact mechanism of action, but it is known that bacteria, bacteriophages and archaea catalyze Holliday junction resolution by introducing symmetric nicks across the Holliday junction {{cite journal | vauthors = Hadden JM, Déclais AC, Carr SB, Lilley DM, Phillips SE | title = The structural basis of Holliday junction resolution by T7 endonuclease I | journal = Nature | volume = 449 | issue = 7162 | pages = 621–4 | date = October 2007 | pmid = 17873858 | doi = 10.1038/nature06158 | bibcode = 2007Natur.449..621H | s2cid = 4403846 }}

. Analysis of crossover junction endodeoxyribonucleases from bacteriophages (T7 endonuclease I), bacteria (RuvC), fungi (GEN1) and humans (hMus81-Eme1) have revealed that the enzymes function in dimers,{{cite journal | vauthors = Shah Punatar R, Martin MJ, Wyatt HD, Chan YW, West SC | title = Resolution of single and double Holliday junction recombination intermediates by GEN1 | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 114 | issue = 3 | pages = 443–450 | date = January 2017 | pmid = 28049850 | pmc = 5255610 | doi = 10.1073/pnas.1619790114 | doi-access = free }} and part of the resolution reaction takes place in a partially dissociated enzyme-substrate intermediate.{{cite journal | vauthors = Zhou R, Yang O, Déclais AC, Jin H, Gwon GH, Freeman AD, Cho Y, Lilley DM, Ha T | title = Junction resolving enzymes use multivalency to keep the Holliday junction dynamic | journal = Nature Chemical Biology | volume = 15 | issue = 3 | pages = 269–275 | date = March 2019 | pmid = 30664685 | pmc = 6377835 | doi = 10.1038/s41589-018-0209-y }}

After a 20-year search, in 2008, a human crossover junction endodeoxyribonuclease, GEN1, was finally identified {{cite journal | vauthors = West SC | title = The search for a human Holliday junction resolvase | journal = Biochemical Society Transactions | volume = 37 | issue = Pt 3 | pages = 519–26 | date = June 2009 | pmid = 19442245 | pmc = 4120095 | doi = 10.1042/BST0370519 }}

. GEN1 performs similar functions and operates by similar mechanisms as previously studied Crossover junction endodeoxyribonuclease in bacteria, archaea, and other eukarya.

The enzyme is thought to play a role in Bloom's syndrome. It has been proposed that Bloom's syndrome involves the induction of DSBs via an unidentified Holliday junction resolvase.{{cite journal | vauthors = Karow JK, Constantinou A, Li JL, West SC, Hickson ID | title = The Bloom's syndrome gene product promotes branch migration of holliday junctions | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 97 | issue = 12 | pages = 6504–8 | date = June 2000 | pmid = 10823897 | pmc = 18638 | doi = 10.1073/pnas.100448097 | bibcode = 2000PNAS...97.6504K | doi-access = free }} It has also been shown that overexpression of Holliday Junction resolvase function is correlated with RAD51-overexpressing cancers.{{cite journal | vauthors = Xia J, Chen LT, Mei Q, Ma CH, Halliday JA, Lin HY, Magnan D, Pribis JP, Fitzgerald DM, Hamilton HM, Richters M, Nehring RB, Shen X, Li L, Bates D, Hastings PJ, Herman C, Jayaram M, Rosenberg SM | title = Holliday junction trap shows how cells use recombination and a junction-guardian role of RecQ helicase | journal = Science Advances | volume = 2 | issue = 11 | pages = e1601605 | date = November 2016 | pmid = 28090586 | pmc = 5222578 | doi = 10.1126/sciadv.1601605 | bibcode = 2016SciA....2E1605X }}

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• {{MeshName|Crossover+junction+endodeoxyribonuclease}}

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Category:EC 3.1.22

Category:Protein superfamilies