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Tony Maxwell
Biological Chemistry Department
Tony Maxwell

DNA topoisomerases in bacteria and plants: mechanism and drug-targeting

Overall aims and objectives: to investigate the structure and mechanism of DNA topoisomerases and associated proteins, in order to further our understanding of key biological processes in which they are involved, and to harness this knowledge for the development of therapeutic agents.

DNA Helix
Solution structure of GyrB monomer

DNA topoisomerases are a vitally important class of proteins involved in the control of the topological state of DNA.  Their major biological functions are in DNA replication, recombination and the control of gene expression.  One of the best characterised DNA topoisomerases is DNA gyrase from Escherichia coli.  Like all topoisomerases gyrase can relax supercoiled DNA, but it is the only enzyme of the group which can also supercoil DNA; DNA supercoiling is driven by ATP hydrolysis.  In addition to studying E. coli gyrase, this laboratory is also working on a number of related enzymes.  These include: topoisomerase IV from E. coli, DNA gyrases from Mycobacterium tuberculosis and Arabidopsis thaliana, and DNA topoisomerase VI from A. thaliana.

Solution structure of GyrA DNA gyrase from E. coli consists of two proteins (A and B) each of MW about 100 kDa; the active enzyme is an A2B2 complex.  The genes for the two proteins have been sequenced and cloned such that the proteins and fragments derived from them may be produced in large amounts.  Gyrase is the target for two clinically important classes of antibiotics, the quinolones and the coumarins, which have been found to inhibit different stages of the supercoiling reaction.
Solution structure of GyrA
 
DNA Helix
Molecular model of MccB17: stick diagram

Topoisomerases provide fascinating systems for the study of DNA-protein interactions and energy coupling in biological systems.  Their study also has clinical relevance from the standpoint of antibacterial and anti-tumour drugs.  The major interests in this laboratory are enzyme structure and mechanism, and the interaction of the enzymes with drugs.  For example, we have crystallised active fragments of the E. coli gyrase A and B proteins and the structure of some of these have been solved to high resolution by x-ray crystallography, including complexes with antibiotics.  This information is yielding valuable insight into mechanistic and drug-targeting aspects of gyrase and other topoisomerases.  In particular we are developing novel strategies for targeting topoisomerases for antimicrobial chemotherapy.  This work involves a wide range of methodologies including molecular biology, bacteriology, protein engineering, enzymology and biophysical methods.

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