The target of most quinolone based antibacterial agents is DNA gyrase, a topoiso

Question

The target of most quinolone based antibacterial agents is DNA gyrase, a topoisomerase enzyme that relieves strain while double-stranded DNA is being unwound by helicase during replication. DNA 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. Thus, DNA gyrase is a good target for antibiotics as molecules that bind to the prokaryotic version may not affect the eukaryotic protein. However, in prokaryotes, mutation of Ser- 83 to Leu gives rise to quinolone resistance. Provide a structure-based rationale for why this might be the case. 4.

Explanation / Answer

Hi
The quinoline is the most commonly used compound to treat bacterial infections. This is very potent and can kill most of the bacteria with small dose. The mode of activity of the quinolone to the topoisomerase Iv (gyrase), depends on the water-metal ion binding. This biding is mediated by hydrogen bonds between the Mg+2 ions and serine81 and glutamic acid85 of the gyrase. If the mutation causes the change of amino acid from serine to leucine, then the hydrogen bonding property changes. The leucine lacks a -OH molecules, which is crucial for H-bond formation with Mg+2. Hence when the mutation occurs, the quinolone-gyrase binding is not efficient. Thus the gyrase enzyme is not inhibited by the quinolone.

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