Sandbox Reserved 828: Difference between revisions
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# Translocation | # Translocation | ||
The A subunit is responsible for the breakage reunion of DNA whereas the B-subunit has the ATPase activity. | The '''A subunit is responsible for the breakage reunion of DNA whereas the B-subunit has the ATPase activity.''' | ||
The introduction of negative supercoils requires the energy of ATP-hydrolysis. 2 ATP are hydrolyzed per reaction (2 B-subunits in the gyrase) so that the linking number (Lk) changes in step of 2. The ATPase activity of the B subunit is partially located in the N-terminal region of protein B whereas the C-terminal is involved in the interaction with the A subunit and DNA. | '''The introduction of negative supercoils requires the energy of ATP-hydrolysis. 2 ATP are hydrolyzed per reaction (2 B-subunits in the gyrase)''' so that the linking number (Lk) changes in step of 2. The '''ATPase activity of the B subunit is partially located in the N-terminal region of protein B whereas the C-terminal is involved in the interaction with the A subunit and DNA.''' | ||
The B subunit has a weak ATPase activity in the absence of A and DNA, eventhought the A subunit is able to bind DNA without the B subunit. Both subunits are required for all the reactions of gyrase. | '''The B subunit has a weak ATPase activity in the absence of A and DNA, eventhought the A subunit is able to bind DNA without the B subunit. Both subunits are required for all the reactions of gyrase.''' | ||
The DNA supercoiling reaction requires in addition to ATP, a divalent cation such as Mg<sup>2+</sup>, and is stimulated in the presence of spermidine. | The DNA supercoiling reaction '''requires in addition to ATP, a divalent cation such as Mg<sup>2+</sup>''', and is stimulated in the presence of spermidine. | ||
Therefore, the gyrase could also catalyse the following reaction : | Therefore, the gyrase could also catalyse the following reaction : | ||
* Relaxation of negative/positive supercoils | * Relaxation of negative/positive supercoils | ||
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The gyrase structure reveals a '''new cluster of conserved residues''', juxtaposing Tyr 122 and Arg 121 from one monomer and His 80, Arg 32 and Lys 42 from the other monomer. '''This cluster may form the active site of the breakage–reunion reaction''', with the other conserved positive charges (Arg 46 and Arg 47) anchoring the non-covalently bound 3' end of the cleaved DNA. | The gyrase structure reveals a '''new cluster of conserved residues''', juxtaposing Tyr 122 and Arg 121 from one monomer and His 80, Arg 32 and Lys 42 from the other monomer. '''This cluster may form the active site of the breakage–reunion reaction''', with the other conserved positive charges (Arg 46 and Arg 47) anchoring the non-covalently bound 3' end of the cleaved DNA. | ||
The gyrase could be inhibited by both the quinolones and | The gyrase could be inhibited by both the [http://en.wikipedia.org/wiki/Quinolone quinolones] and [http://en.wikipedia.org/wiki/Coumarin coumarins]. | ||
Coumarins prevent the B-subunit of the gyrase from hydrolyzing the ATP, so that the gyrase can't come back to its starting state for another round of supercoiling. The mecanism is not yet well known. | |||
'''Coumarins prevent the B-subunit of the gyrase from hydrolyzing the ATP''', so that the gyrase can't come back to its starting state for another round of supercoiling. The mecanism is not yet well known. | |||
However, some mutations offers quinolone resistance, most of them involved a part of the GyrA sequence : between the amino | |||
'''Quinolones''' inhibit DNA supercoiling by gyrase, it has even the ability to '''induce DNA cleavage''' instead. It appears that '''these drugs will arrest any gyrase rection involving double-strand DNA breakage.''' | |||
However, some mutations offers quinolone resistance, most of them involved a part of the GyrA sequence : between the amino acids 67 and 106. | |||
There are also others antibiotics, like the Cinodine which binds DNA and inhibits its supercoiling by gyrase. | There are also others antibiotics, like the Cinodine which binds DNA and inhibits its supercoiling by gyrase. | ||
