Chemistry: molecular biology and microbiology – Enzyme – proenzyme; compositions thereof; process for... – Isomerase
Patent
1997-01-24
1999-12-14
Wax, Robert A.
Chemistry: molecular biology and microbiology
Enzyme , proenzyme; compositions thereof; process for...
Isomerase
4352523, 43525411, 4353201, 536 232, C01N 990, C01N 120, C07H 2104
Patent
active
060016310
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a novel topoisomerase IV, the nucleotide sequences encoding this enzyme, their corresponding vectors and the use of this enzyme for screening biologically active products.
Topoisomerases are enzymes capable of modifying the topological configuration of DNA rings, of making knots therein or of interlacing separated rings. They are thus involved in the replication, transcription and recombination of the entire genetic information (Wang et al., 1990). The mechanism of all these topological conversions is the same: the ring is opened so that a segment of DNA passes through the gap before the ends are rejoined. Two types of topoisomerase are involved in these conversions: type I topoisomerases which cut a single DNA strand and type II topoisomerases which cut both strands simultaneously.
Up until now, two type II bacterial topoisomerases have been identified and studied more particularly: gyrase from Escherichia coli (Gellert et al., 1976), and more recently, DNA topoisomerase IV from E. coli (Kato et al., 1990).
Gyrase is a .alpha..sub.2 .beta..sub.2 tetramer whose .alpha. or GyrA and .beta. or GyrB subunits are encoded by the gyrA and gyrB genes respectively. Bacterial gyrases are the only known topoisomerases capable of supercoiling relaxed DNA rings in the presence of ATP.
As regards more particularly DNA topoisomerase IV from E. coli, it relaxes supercoiled plasmid DNA, unknots T4 phage DNA and unwinds (or decatenates) kinetoplast DNA (Kato et al., 1992; Peng et al., 1993). The sequence of its corresponding genes, parC and parE from E. coli, has made it possible to demonstrate regions of high similarity between the subunits of gyrase and those of this topoisomerase IV, ParC with GyrA (35.6% over the entire sequence) and ParE with GyrB (40.1% over the entire sequence) respectively (Kato et al., 1990).
E. coli gyrase has also been identified as being a primary target of fluoroquinolones (Hooper et al., 1993). It has thus been demonstrated that E. coli strains mutated at the level of the Ser83 residue in the GyrA subunit have a high resistance to fluoroquinolones (Maxwell, 1992). Fluoroquinolones bind less to DNA-mutated gyrase complexes than to DNA-wild-type gyrase complexes. Indeed, other point mutations, mapped in the region between residues 67 and 106 of GyrA, lead to strains resistant to fluoroquinolones. This region is called QRDR (Yoshida et al., 1990; Cullen et al., 1989). Similar results have been published with strains of Staphylococcus aureus resistant to fluoroquinolones (Goswitz et al., 1992; Sreedharan et al., 1990). Gyrase is therefore nowadays recognized as being the primary target of quinolones. However, a clinical strain of Staphylococcus aureus, not containing any mutation in the QRDR region of GyrA, has also been described as resistant to fluoroquinolones (Sreedharan et al., 1991).
Nowadays, this phenomenon of resistance developed by Staphylococcus aureus bacteria towards antibiotics and more particularly towards fluoroquinolones is being increasingly encountered at the therapeutic level. It would be particularly important to be able to lift this resistance and this involves a characterization of all the parameters which are associated with it.
The main objective of the present invention is precisely the identification, sequencing and characterization of nucleic sequences encoding subunits of a novel topoisomerase, topoisomerase IV of Staphylococcus aureus, composed of two subunits, GrlA and GrlB.
Unexpectedly, the applicant has found that the primary target of the fluoroquinolones in S. aureus is a topoisomerase IV and not gyrase. It has thus demonstrated that clinical strains of S. aureus, in which the QRDR region of the GyrA subunit of gyrase is identical to the wild-type sequence, develop nevertheless a resistance to fluoroquinolones because of a mutation which they possess in the region of the GrlA subunit of topoisomerase IV, homologous to the QRDR region.
The first subject of the present invention is a nucleotide sequence encoding at least one subuni
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Blanche Francis
Cameron Beatrice
Crouzet Joel
Famechon Alain
Ferrero Lucia
Rhone-Poulenc Rorer S.A.
Wax Robert A.
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