1,19-seco-Avermectin Analogues from a Δ<i>aveCDE</i> Mutant <i>Streptomyces avermectinius</i> Strain

Three new 1,19-seco-avermectin (AVE) analogues were isolated from the <i>ΔaveCDE</i> mutant <i>Streptomyces avermectinius</i> strain. Their structures were elucidated by detailed spectroscopic analysis. This is the first report of 1,19-seco-AVE analogues. In an <i>in vitro</i> assay these compounds displayed cytotoxicity against Saos-2, MG-63, and B16 cell lines

Spiroketal Formation and Modification in Avermectin Biosynthesis Involves a Dual Activity of AveC

Avermectins (AVEs), which are widely used for the treatment of agricultural parasitic diseases, belong to a family of 6,6-spiroketal moiety-containing, macrolide natural products. AVE biosynthesis is known to employ a type I polyketide synthase (PKS) system to assemble the molecular skeleton for further functionalization. It remains unknown how and when spiroketal formation proceeds, particularly regarding the role of AveC, a unique protein in the pathway that shares no sequence homology to any enzyme of known function. Here, we report the unprecedented, dual function of AveC by correlating its activity with spiroketal formation and modification during the AVE biosynthetic process. The findings in this study were supported by characterizing extremely unstable intermediates, products and their spontaneous derivative products from the simplified chemical profile and by comparative analysis of <i>in vitro</i> biotransformations and <i>in vivo</i> complementations mediated by AveC and MeiC (the counterpart in biosynthesizing the naturally occurring, AVE-like meilingmycins). AveC catalyzes the stereospecific spiroketalization of a dihydroxy-ketone polyketide intermediate and the optional dehydration to determine the regiospecific saturation characteristics of spiroketal diversity. These reactions take place between the closures of the hexene ring and 16-membered macrolide and the formation of the hexahydrobenzofuran unit. MeiC can replace the spirocyclase activity of AveC, but it lacks the independent dehydratase activity. Elucidation of the generality and specificity of AveC-type proteins allows for the rationalization of previously published results that were not completely understood, suggesting that enzyme-mediated spiroketal formation was initially underestimated, but is, in fact, widespread in nature for the control of stereoselectivity

KEGG analysis of differentially methylated genes between the streptomycin-resistant and normal groups.

KEGG analysis of differentially methylated genes between the streptomycin-resistant and normal groups.</p

Differentially methylated genes between the streptomycin-resistant and normal groups.

Differentially methylated genes between the streptomycin-resistant and normal groups.</p

Transcriptome atlas and KEGG analysis of differentially expressed genes between the streptomycin-resistant and normal groups.

A) The heatmap was used to show the differentially expressed genes between the streptomycin-resistant and normal groups. B) KEGG analysis was used to compare the differentially expressed genes in the streptomycin-resistant and normal groups. Rich factor indicated the ratio of the number of differentially expressed genes enriched in each KEGG term to the number of all annotated genes in the KEGG term. Negative binomial distribution model was used to calculate P-value.</p

Table_1_mbtD and celA1 association with ethambutol resistance in Mycobacterium tuberculosis: A multiomics analysis.xlsx

Ethambutol (EMB) is a first-line antituberculosis drug currently being used clinically to treat tuberculosis. Mutations in the embCAB operon are responsible for EMB resistance. However, the discrepancies between genotypic and phenotypic EMB resistance have attracted much attention. We induced EMB resistance in Mycobacterium tuberculosis in vitro and used an integrated genome–methylome–transcriptome–proteome approach to study the microevolutionary mechanism of EMB resistance. We identified 509 aberrantly methylated genes (313 hypermethylated genes and 196 hypomethylated genes). Moreover, some hypermethylated and hypomethylated genes were identified using RNA-seq profiling. Correlation analysis revealed that the differential methylation of genes was negatively correlated with transcription levels in EMB-resistant strains. Additionally, two hypermethylated candidate genes (mbtD and celA1) were screened by iTRAQ-based quantitative proteomics analysis, verified by qPCR, and corresponded with DNA methylation differences. This is the first report that identifies EMB resistance-related genes in laboratory-induced mono-EMB-resistant M. tuberculosis using multi-omics profiling. Understanding the epigenetic features associated with EMB resistance may provide new insights into the underlying molecular mechanisms.</p