Genome mining is a rational approach to discovering new natural products. The genome sequence analysis of Streptomyces sp. LZ35 revealed the presence of a putative ansamycin gene cluster (nam). Constitutive overexpression of the pathway-specific transcriptional regulatory gene nam1 successfully activated the nam gene cluster, and three novel naphthalenic octaketide ansamycins were discovered with unprecedented n-pentylmalonyl-CoA or n-butylmalonyl-CoA extender units. This study represents the first example of discovering novel ansamycin scaffolds via activation of a cryptic gene cluster.

Ansamycins are a family of macrolactams characterized by an aromatic chromophore with an aliphatic chain (ansa chain) connected back to a nonadjacent position through an amide bond. This family has shown a high degree of druggability exemplified by rifamycins, maytansinoids, and geldanamycins. In this study, the isolation of two novel ansamycin macrodilactams with unprecedented features, juanlimycins A (1) and B (2), from Streptomyces sp. LC6 were reported. The structures of 1 and 2 were assigned on the basis of analysis of NMR spectroscopic data and X-ray single crystal diffraction.

Background Alteramide B (ATB), isolated from Lysobacter enzymogenes C3, was a new polycyclic tetramate macrolactam (PTM). ATB exhibited potent inhibitory activity against several yeasts, particularly Candida albicans SC5314, but its antifungal mechanism is unknown. Methods The structure of ATB was established by extensive spectroscopic analyses, including high-resolution mass spectrometry, 1D- and 2D-NMR, and CD spectra. Flow cytometry, fluorescence microscope, transmission electron microscope, molecular modeling, overexpression and site-directed mutation studies were employed to delineate the anti-candida molecular mechanism of ATB. Results ATB induced apoptosis in C. albicans through inducing reactive oxygen species (ROS) production by disrupting microtubules. Molecular dynamics studies revealed the binding patterns of ATB to the β-tubulin subunit. Overexpression of the wild type and site-directed mutants of the β-tubulin gene (TUBB) changed the sensitivity of C. albicans to ATB, confirming the binding of ATB to β-tubulin, and indicating that the binding sites are L215, L217, L273, L274 and R282. In vivo, ATB significantly improved the survival of the candidiasis mice and reduced fungal burden. Conclusion The molecular mechanism underlying the ATB-induced apoptosis in C. albicans is through inhibiting tubulin polymerization that leads to cell cycle arrest at the G2/M phase. The identification of ATB and the study of its activity provide novel mechanistic insights into the mode of action of PTMs against the human pathogen. General significance This study shows that ATB is a new microtubule inhibitor and a promising anti-Candida lead compound. The results also support β-tubulin as a potential target for anti-Candida drug discovery.

Ultraviolet B (UVB) irradiation has been known to cause skin damage, which is associated with oxidative stress, DNA damage, and apoptosis. Echinacoside is a phenylethanoid glycoside isolated from Herba Cistanches, which exhibits strong antioxidant activity. In this study, we evaluate the photoprotective effect of echinacoside on UVB-induced skin damage and explore the potential molecular mechanism. BALB/c mice and HaCaT cells were treated with echinacoside before UVB exposure. Histopathological examination was used to evaluate the skin damage. Cell viability, lactate dehydrogenase (LDH) levels, antioxidant enzyme activities, reactive oxygen species (ROS) generation, DNA damage, and apoptosis were measured as well. Western blot was used to measure the expression of related proteins. The results revealed that pretreatment of echinacoside ameliorated the skin injury; attenuated oxidative stress, DNA damage, and apoptosis caused by UVB exposure; and normalized the protein levels of ATR, p53, PIAS3, hnRNP K, PARP, and XPA. To summarize, echinacoside is beneficial in the prevention of UVB-induced DNA damage and apoptosis of the skin in vivo and in vitro.

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Ten new benzenic ansamycins, 5,10-seco-neoansamycins A-J (1-10), were isolated from the nam7-disrupted mutant strain SR201nam1OEΔnam7. These are the benzenic counterparts of the neoansamycins, which provide direct evidence that the putative hydroxylase Nam7 is involved in the formation of naphthalenic ring in neoansamycin biosynthesis and connect benzenic and naphthalenic ansamycins for the first time.

Five new polyketides of the ansamycin class, named ansavaricins A–E (1–5), together with three known streptovaricins 6–8, were isolated from the Streptomyces sp. S012 strain.

This study reported the isolation and characterization of 11 rifamycin congeners including six new ones (1–6) from the agar fermentation extract of Amycolatopsis mediterranei S699. Compounds 1 and 2 are rifamycin glycosides named as rifamycinosides A and B, respectively. Their polyketide skeleton represents a novel cleavage pattern of the rifamycin ansa chain. Compounds 6 and 8 showed potential T3SS inhibitory activity, and 6 induced G2/M phase arrest and caused DNA damage in HCT116 cells.