Characterization of Highly Reductive Modification of Tetracycline D-Ring Reveals Enzymatic Conversion of Enone to Alkane

Tetracyclines are an eminent family of type II polyketides which possess a variety of decoration on the skeletons. However, apart from the oxidative modification in aureolic acid compounds, there are few cases on the further conversion of α, β-unsaturated ketones in the tetracycline D-ring. Here, we identified two reductases (TjhO5 and TjhD4) that highly reduced the α,β-unsaturated ketone of D-ring in the biosynthesis of unconventional tetracyclines. By identifying related intermediates and conducting isotope incorporation experiments, we demonstrated that the entire transformation could be accomplished by TjhO5 and TjhD4 collectively via two distinct pathways involving different enzymatic mechanisms. A distinctive deoxygenation mechanism was possibly involved in the TjhO5-mediated continuous reduction of C = O to CH2. These findings highlight the unprecedent post-modification of tetracyclines and facilitate further engineering to enrich the structural diversities.

Metathramycin, a new bioactive aureolic acid discovered by heterologous expression of a metagenome derived biosynthetic pathway

Heterologous expression of an aromatic polyketide biosynthetic gene cluster recovered from a New Zealand soil metagenome library resulted in the discovery of new bioactive aureolic acids.

Aureolic Acid Group of Agents as Potential Antituberculosis Drugs

Mycobacterium tuberculosis is one of the most dangerous pathogens. Bacterial resistance to antituberculosis drugs grows each year, but searching for new drugs is a long process. Testing for available drugs to find active against mycobacteria may be a good alternative. In this work, antibiotics of the aureolic acid group were tested on a model organism Mycobacterium smegmatis. We presumed that antibiotics of this group may be potential G4 ligands. However, this was not confirmed in our analyses. We determined the antimicrobial activity of these drugs and revealed morphological changes in the cell structure upon treatment. Transcriptomic analysis documented increased expression of MSMEG_3743/soj and MSMEG_4228/ftsW, involved in cell division. Therefore, drugs may affect cell division, possibly disrupting the function of the Z-ring and the formation of a septum. Additionally, a decrease in the transcription level of several indispensable genes, such as nitrate reductase subunits (MSMEG_5137/narI and MSMEG_5139/narX) and MSMEG_3205/hisD was shown. We concluded that the mechanism of action of aureolic acid and its related compounds may be similar to that bedaquiline and disturb the NAD+/NADH balance in the cell. All of this allowed us to conclude that aureolic acid derivatives can be considered as potential antituberculosis drugs.