The molecular basis of action of the toxin Microcin B17 on DNA gyrase

We are in danger of heading for a crisis in infectious diseases. The combined effects of multi-drug-resistant bacterial infections, such as MRSA and C. difficile, and the lack of new antibiotics being produced by pharmaceutical companies, means that academic labs need to make a more significant contribution to solving this problem. We are studying an enzyme from bacteria called DNA gyrase, which is already the target for antibiotics such as Cipro (ciprofloxacin), the drug used to combat anthrax during the scare in the USA in 2001. Unfortunately, due to resistance problems, Cipro is no longer as effective as it was and the search is on for antibiotics to replace it. Microcin B17 is a toxin produced by bacteria to kill other bacteria, and it works in a manner similar to Cipro but is unlikely to be affected by the same resistance problems. We aim to understand the molecular details of how Microcin B17 works such that this information can be used in the future design of new antibiotics that can potentially replace Cipro.

Finding new molecules that are potential leads for antibacterial agents is a significant challenge. There are relatively few validated antibacterial targets; the considerable efforts of genomics/proteomics have largely failed to deliver many new targets. Nature has already revealed what the good targets are, and among these is bacterial DNA gyrase. The fluoroquinolones, which target gyrase, have been spectacularly successful, but resistance problems have now rendered them considerably less effective. Therefore we need new agents with comparable properties. Microcin B17 (MccB17) acts on gyrase in a similar, but distinct, way to quinolones; its binding site and exact mode of action are different. By establishing the molecular basis of MccB17's action and by exploring novel small molecules that are fragments/analogues of MccB17, we believe we can provide insight into novel gyrase-inhibitor interactions that will subsequently contribute to the development of new anti-bacterial agents. Our approach entails: producing novel microcin analogues, by genetic and chemical means, that can be assessed for their potential as novel inhibitors and utilised in the analysis of MccB17 action; and defining the MccB17 binding site by identifying novel mutations in gyrase, performing toxin-target cross-linking studes, and structural analysis by crystallography and NMR.

Who will benefit?
1. Academic researchers in the areas of ligand-protein interaction, inhibitor design and topoisomerase research (see Academic Beneficiaries).
2. Pharmaceutical companies involved in antibacterial drug discovery (e.g. Pfizer, AstraZeneca, GSK): providing new ideas for drug discovery.
3. UK government in terms of showing that investment is being channelled into areas that will underpin future drug discovery.
4. Charities concerned with the threat of third-world diseases (e.g. tuberculosis): an example would be the Gates Foundation, which has a major effort on TB.
5. For the general public, the work offers hope for potential new treatments for infectious diseases.

How will they benefit?
a. Improved understanding of ligand-target interactions.
b. New ideas for drug discovery.
c. Evaluation of the potential of MccB17 derivatives and analogues as future candidates for drug development.

What will be done to ensure that they have the opportunity to benefit from this research?
i. Publication in high-profile journals.
ii. Media involvement via JIC TOC Comms.
iii. Collaborations with UK and overseas partners (industrial and academic).
iv. Investigation of exploitation potential via PBL.
v. Establishment of BBSRC-CASE studentships based on work stimulated by this project.
vi. Continued engagement with local schools.