The discovery of Streptomyces-produced streptomycin founded the age of tuberculosis therapy. Despite the subsequent development of a curative regimen for this disease, tuberculosis remains a worldwide problem, and the emergence of multidrug-resistant Mycobacterium tuberculosis has prioritized the need for new drugs. Here we show that new optimized derivatives from Streptomyces-derived griselimycin are highly active against M. tuberculosis, both in vitro and in vivo, by inhibiting the DNA polymerase sliding clamp DnaN. We discovered that resistance to griselimycins, occurring at very low frequency, is associated with amplification of a chromosomal segment containing dnaN, as well as the ori site. Our results demonstrate that griselimycins have high translational potential for tuberculosis treatment, validate DnaN as an antimicrobial target, and capture the process of antibiotic pressure-induced gene amplification.
Microorganisms form diverse multispecies communities in various ecosystems. The high abundance of fungal and bacterial species in these consortia results in specific communication between the microorganisms. A key role in this communication is played by secondary metabolites (SMs), which are also called natural products. Recently, it was shown that interspecies “talk” between microorganisms represents a physiological trigger to activate silent gene clusters leading to the formation of novel SMs by the involved species. This review focuses on mixed microbial cultivation, mainly between bacteria and fungi, with a special emphasis on the induced formation of fungal SMs in co-cultures. In addition, the role of chromatin remodeling in the induction is examined, and methodical perspectives for the analysis of natural products are presented. As an example for an intermicrobial interaction elucidated at the molecular level, we discuss the specific interaction between the filamentous fungi Aspergillus nidulans and Aspergillus fumigatus with the soil bacterium Streptomyces rapamycinicus, which provides an excellent model system to enlighten molecular concepts behind regulatory mechanisms and will pave the way to a novel avenue of drug discovery through targeted activation of silent SM gene clusters through co-cultivations of microorganisms.
The p73b protein shares structural and functional similarities with the tumor suppressor gene product p53. Both proteins activate transcription from p53-responsive promoters. p53's activity is antagonized by the mdm2 protein (also termed hdm2 in human cells). Complex formation between p53 and mdm2 results in p53's transcriptional inactivation and destabilization. Here we show that overexpression of mdm2 reduces p73b's ability to activate transcription, too. The mdm2 protein forms a speci®c complex with p73b in vitro with an eciency comparable to p53-binding. Further, both p73b and p53 relocalize a transport-defective mutant of mdm2 from the cytoplasm to the nucleus, arguing that complex formation occurs in vivo as well. Mutational analysis suggests that the interaction between p73b and mdm2 follows structural principles analogous to the p53-mdm2-complex. Whereas p53 is destabilized in the presence of mdm2, the amount of intracellular p73b was not detectably reduced by mdm2. The carboxyterminal RING ®nger domain of mdm2 was found to be required to reduce the intracellular abundance of p53, but it was dispensable for transcriptionally inactivating either p53 or p73b. Our results suggest that the autoregulatory feedback loop between p53 and mdm2 also controls p73's activity, but that mdm2-mediated protein degradation is unique to p53.
Stimulating encounter: The intimate, physical interaction between the soil-derived bacterium Streptomyces rapamycinicus and the human pathogenic fungus Aspergillus fumigatus led to the activation of an otherwise silent polyketide synthase (PKS) gene cluster coding for an unusual prenylated polyphenol (fumicycline A). The meroterpenoid pathway is regulated by a pathway-specific activator gene as well as by epigenetic factors.
The biosynthesis of griselimycins in Streptomyces DSM 40835 and the pathway that stereospecifically converts l-leucine to (2S,4R)-4-methyl-proline are reported by means of biochemical and structural analysis.
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