|
X-ray crystallography has allowed German researchers to focus on an important metabolic reaction that exists in many different aggressive microorganisms, including all pathogenic bacteria and the malaria parasite. The revealed structure could offer a promising new target for novel drugs. From the day the first antibiotic was used against pathogenic bacteria, they have succumbed to evolution by natural selection as mutant microbial strains survive and pass on their resistance to their progeny. Resistance has been a problem for decades, but emergent strains of harmful bacteria are becoming more widespread and even defeating multiple drug regimes usually considered the last line of defence. As such, the medical community is now warning that fatalities from various kinds of resistant bacteria could increase dramatically in the very near future. Now, researchers at the Technische Universität München (TUM), Germany, have found a promising target for a new class of antibiotics that evade the bacterial resistance movement. Antibiotics usually work by interfering with some essential metabolic process, bacterial cell wall construction, or simply burst the bacterium wide open by opening up pores in its surface. Researchers are always on the look out for another mechanism to exploit in the design of new antibiotics. The preference is for a mechanism vital to the sustenance of the bacteria and its reproduction but that has no biochemical counterpart in humans and so would be less likely to harm the patient. Tobias Gräwert, Felix Rohdich, Ingrid Span, Adelbert Bacher, Wolfgang Eisenreich, Jörg Eppinger, and Michael Groll at TUM have homed in on one such vital process. Almost all organisms produce the natural products known as terpenes and steroids from the small isoprene building blocks dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP). Mammals exploit the so-called mevalonate pathway for making theirs while human pathogens, including several bacteria and the malaria parasite Plasmodium falciparum, take an alternative route. Early research into bacterial synthesis of isoprene building blocks was begun in the 1990s by Adelbert Bacher, Wolfgang Eisenreich, and Felix Rohdich, and they have uncovered most of the required steps in metabolic pathway. However, the structural basis of the terminal step in bacterial isoprene biosynthesis remained elusive. Earlier measurements suggested that the active core must be an iron-sulfur cluster with three iron and four sulfur atoms. But other researchers questioned the results and for many years the crystal structure of the enzyme remained indeterminate. The main problem facing crystallographers was the oxygen sensitivity of the IspH enzyme, which causes it to denature rapidly in air. A research group at Justus-Liebig University in Giessen recently determined the enzyme's "open" state by crystallography but this structure did not provide an explanation for the process catalysed by the enzyme. The TUM team has now succeeded in carrying out a detailed structural study that reveals the precise folding pattern of the protein chain and the chemical environment of the active site cavity. The IspH enzyme it seems has an unusual structure resembling a shamrock. The team explains that creating mutant versions of the enzyme in laboratory strains of Escherichia coli bacteria and then using computer simulations of the structures allowed them to confirm that three iron and four sulfur atoms are present in the central active site of the enzyme. "Now that the location, the chemical process and the involved helpers of the IspH reaction have been identified," explains Groll, "We have a new angle of attack for developing substances that block the terminal step in the bacterial synthesis of isoprene building blocks, thereby killing pathogens in a very targeted way. Since the enzyme and the associated reaction do not appear in mammals these compounds should have few or no side effects in humans." The next stage in the research will be to model the system and so look for ligands and putative inhibitors for the process, Groll told SpectroscopyNOW. "We need to understand substrate access, docking and product release," he explains. "It would be interesting to get further insights in this mechanism which might allow us to obtain a comprehensive overview of the catalyzed reaction."
Related links:
|
Groll, crystallising new antibiotic drug target |
