WordNet

write by means of a keyboard with types; "type the acceptance letter, please" (同)typewrite
a small metal block bearing a raised character on one end; produces a printed character when inked and pressed on paper; "he dropped a case of type, so they made him pick them up"
(biology) the taxonomic group whose characteristics are used to define the next higher taxon
a subdivision of a particular kind of thing; "what type of sculpture do you prefer?"
all of the tokens of the same symbol; "the word `element contains five different types of character"
printed characters; "small type is hard to read"
identify as belonging to a certain type; "Such people can practically be typed" (同)typecast
the 9th letter of the Roman alphabet (同)i
the 4th letter of the Roman alphabet (同)d

PrepTutorEJDIC

〈C〉(…の)『型』,タイプ,類型,種類(kind)《+of+名》 / 〈C〉(その種類の特質を最もよく表している)『典型』,手本,模範《+of+名》 / 〈U〉《集合的に》活字;〈C〉(1個の)活字 / 〈U〉(印刷された)字体,活字 / 〈C〉(貨幣・メダルなどの)模様,図柄 / 〈C〉血液型(blood group) / …‘を'タイプに打つ / (…として)…‘を'分類する《+名+as+名(doing)》 / …‘の'型を決める / タイプライターを打つ
『私は』私が
iodineの化学記号
deuteriumの化学記号
deoxyribonucleic acidディオキシリボ核酸

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/10/20 17:20:56」(JST)

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DNA gyrase, often referred to simply as gyrase, is an enzyme that relieves strain while double-strand DNA is being unwound by helicase.^[1]^[2] It is also known as DNA topoisomerase II. This causes negative supercoiling of the DNA. Bacterial DNA gyrase is the target of many antibiotics, including nalidixic acid, novobiocin, and ciprofloxacin. It supercoils (or relaxes positive supercoils) into DNA by looping the template so as to form a crossing, then cutting one of the double helices and passing the other through it before releasing the break, changing the linking number by two in each enzymatic step. This process occurs in prokaryotes (in particular, in bacteria), whose single circular DNA is cut by DNA gyrase and the two ends are then twisted around each other to form supercoils. Gyrase has been found in the apicoplast of the malarial parasite Plasmodium falciparum, a unicellular eukaryote.^[3]^[4]

The unique ability of gyrase to introduce negative supercoils into DNA is what allows bacterial DNA to have free negative supercoils. The ability of gyrase to relax positive supercoils comes into play during DNA replication and prokaryotic transcription. The right-handed nature of the DNA double helix causes positive supercoils to accumulate ahead of a translocating enzyme, in the case of DNA replication, a DNA polymerase. The ability of gyrase (and topoisomerase IV) to relax positive supercoils allows superhelical tension ahead of the polymerase to be released so that replication can continue.

Mechanochemical model of gyrase activity

A single molecule study^[5] has characterized gyrase activity as a function of DNA tension (applied force) and ATP, and proposed a mechanochemical model. Upon binding to DNA (the "Gyrase-DNA" state), there is a competition between DNA wrapping and dissociation, where increasing DNA tension increases the probability of dissociation. Upon wrapping and ATP hydrolysis, two negative supercoils are introduced into the template, providing opportunities for subsequent wrapping and supercoiling events. The number of superhelical turns introduced into an initially relaxed circular DNA has been calculated to be approximately equal to the number of ATP molecules hydrolyzed by gyrase.^[6] Therefore, it can be suggested that two ATP molecules are hydrolyzed per cycle of reaction by gyrase, leading to the introduction of a linking difference of -2.^[7]

Inhibition by antibiotics

Gyrase is present in prokaryotes and some eukaryotes, but the enzymes are not entirely similar in structure or sequence, and have different affinities for different molecules. This makes gyrase a good target for antibiotics. Two classes of antibiotics that inhibit gyrase are:

The aminocoumarins (including novobiocin). Aminocoumarins work by competitive inhibition of energy transduction of DNA gyrase by binding to the ATPase active site located on the GyrB subunit.
The quinolones (including nalidixic acid and ciprofloxacin). Quinolones bind to these enzymes and prevent them from decatenation replicating DNA. Quinolone-resistant bacteria frequently harbor mutated topoisomerases that resist quinolone binding.

DNA gyrase has two subunits, which in turn have two subunits each, i.e. 2A and 2B SUBUNITS. The A and B subunits together bind to DNA, hydrolyze ATP, and introduce negative supertwists. The A subunit carries out nicking of DNA, B subunit introduces negative supercoils, and then A subunit reseals the strands. Fluoroquinolones bind to the A subunit and interfere with its strand cutting and resealing function.

The subunit A is selectively inactivated by antibiotics such as oxolinic and nalidixic acids. The subunit B is selectively inactivated by antibiotics such as coumermycin A₁ and novobiocin. Inhibition of either subunit blocks supertwisting activity.^[8]

References

^ Wigley, D.B.; Davies, G.J.; Dodson, E.J.; Maxwell, A; Dodson, G (1991). "Crystal structure of an N-terminal fragment of the DNA gyrase B protein". Nature 351 (6328): 624–629. Bibcode:1991Natur.351..624W. doi:10.1038/351624a0. PMID 1646964.
^ Morais Cabral, J. H.; Jackson, A. P.; Smith, C. V.; Shikotra, N; Maxwell, A; Liddington, R. C. (1997). "Crystal structure of the breakage-reunion domain of DNA gyrase". Nature 388 (6645): 903–6. Bibcode:1997Natur.388..903M. doi:10.1038/42294. PMID 9278055.
^ "Molecular Cloning of Apicoplast-Targeted Plasmodium falciparum DNA Gyrase Genes: Unique Intrinsic ATPase Activity and ATP-Independent Dimerization of PfGyrB Subunit". EUKARYOTIC CELL: 398–412. 2007.
^ "A unique 45 amino acid region in the Toprim domain of Plasmodium falciparum GyraseB is essential for its activity. (2009)". Eukaryotic Cell 11 (8): 1759–69.
^ Gore J, Bryant Z, Stone MD, Nollmann M, Cozzarelli NR, Bustamante C, "Mechanochemical Analysis of DNA Gyrase Using Rotor Bead Tracking", Nature 2006 Jan 5 (Vol. 439): 100-104.
^ Sugino, Akio (1980-10-07). "The Intrinsic ATPase of DNA Gyrase". Journal of Biological Chemistry 255 (13).
^ Reece, Richard (1991). "DNA Gyrase: Structure and Function". Critical Reviews in Biochemistry and Molecular Biology 26 (3/4): 335–375. doi:10.3109/10409239109114072.
^ Engle, E C; Manes, S H; Drlica, K. "Differential effects of antibiotics inhibiting gyrase". Journal of Bacteriology.

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English Journal

Recombinagenic and mutagenic activities of fluoroquinolones in Drosophila melanogaster.

Thomé S, Bizarro CR, Lehmann M, Abreu BR, Andrade HH, Cunha KS, Dihl RR.SourceLaboratório da Toxicidade Genética (TOXIGEN), Programa de Pós-Graduação em Genética e Toxicologia Aplicada (PPGGTA), Universidade Luterana do Brasil, Canoas, RS, Brazil.
Mutation research.Mutat Res.2012 Feb 18;742(1-2):43-7. Epub 2011 Nov 28.
Fluoroquinolones are widely used in human and in veterinary medicine due to their broad-spectrum antibacterial activity. They act by inhibiting type II DNA topoisomerases (gyrase and topoisomerase IV). Because of the sequence homology between prokaryotic and eukaryotic topoisomerases II, fluoroquino
PMID 22142834

Purification, crystallization and preliminary X-ray crystallographic studies of the Mycobacterium tuberculosis DNA gyrase CTD.

Darmon A, Piton J, Roué M, Petrella S, Aubry A, Mayer C.SourceUnité de Microbiologie Structurale, Institut Pasteur, CNRS URA 2185, 25 Rue du Dr Roux, 75015 Paris, France.
Acta crystallographica. Section F, Structural biology and crystallization communications.Acta Crystallogr Sect F Struct Biol Cryst Commun.2012 Feb 1;68(Pt 2):178-80. Epub 2012 Jan 26.
Mycobacterium tuberculosis DNA gyrase, a nanomachine involved in regulation of DNA topology, is the only type II topoisomerase present in this organism and hence is the sole target of fluoroquinolone in the treatment of tuberculosis. The C-terminal domain (CTD) of the DNA gyrase A subunit possesses
PMID 22297993

Comparative analysis of stress responses of H9c2 rat cardiomyoblasts following treatment with doxorubicin and tBOOH.

Döhrmann M, Schorr A, Hülsenbeck J, Rasmussen TL, Issinger OG, Fritz G.SourceUniversity Medical Center of the Johannes Gutenberg University Mainz, Institute of Toxicology, Mainz, Germany.
Experimental cell research.Exp Cell Res.2012 Jan 13. [Epub ahead of print]
Cardiotoxicity is the major dose-limiting adverse effect of anthracyclines and is hypothesized to result from damage induced by reactive oxygen species (ROS) or inhibition of topoisomerase II. Here, we comparatively analyzed the effect of doxorubicin and the organic peroxide tertiary-butylhydroperox
PMID 22265794

Japanese Journal

Experimental and Clinical Studies on Fluoroquinolone-insusceptible Escherichia coli Isolated from Patients with Urinary Tract Infections from 1994 to 2007

Wada Koichiro,Kariyama Reiko,Mitsuhata Ritsuko,Uehara Shinya,Watanabe Toyohiko,Monden Koichi,Kumon Hiromi
Acta Medica Okayama 63(5), 263-272, 2009-10
… We analyzed the mutations in quinolone resistance-determining regions of DNA gyrase (gyrA) and topoisomerase IV (parC). … Amino acid replacements of type II topoisomerases were frequently observed at positions 83 and 87 in GyrA and at positions 80 and 84 in ParC. …
NAID 120002313204

3P-261 II型DNAトポイソメラーゼの手品のような反応を直接みる(バイオイメージング,口頭発表,第47回日本生物物理学会年会)

余語克紀,Ogawa Taisaku,Obata Saki,Nakajima Gen,Suzuki Junpei,Kinosita Kazuhiko
生物物理 49(SUPPLEMENT_1), S194, 2009-09-20
NAID 110008102115

3TP3-02 II型DNAトポイソメラーゼの手品のような反応を直接みる(バイオイメージング,第47回日本生物物理学会年会)

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生物物理 49(SUPPLEMENT_1), S61, 2009-09-20
NAID 110008101291

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★リンクテーブル★

リンク元	「トポイソメラーゼII」「DNAトポイソメラーゼII」「II型DNAトポイソメラーゼ」「DNA topoisomerase II」
拡張検索	「archaeal type II DNA topoisomerase」「eukaryotic type II DNA topoisomerase」「bacterial type II DNA topoisomerase」
関連記事	「type」「D」「II」「I」「DNA topoisomerase」

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