Search

Cyclopeptide alkaloids are an abundant class of plant cyclopeptides with over 200 analogs described and bioactivities ranging from analgesic to antiviral. While these natural products have been known for decades, their biosynthetic basis remains unclear. Using a transcriptome‐mining approach, we link the cyclopeptide alkaloids from Ceanothus americanus to dedicated RiPP precursor peptides and identify new, widely distributed split BURP peptide cyclase containing gene clusters. Guided by our bioinformatic analysis, we identify and isolate new cyclopeptides from Coffea arabica, which we named arabipeptins. Reconstitution of the enzyme activity for the BURP found in the biosynthesis of arabipeptin A validates the activity of the newly discovered split BURP peptide cyclases. These results expand our understanding of the biosynthetic pathways responsible for diverse cyclic plant peptides and suggest that these side chain cross‐link modifications are widely distributed in eudicots. [ABSTRACT FROM AUTHOR]

Sixteen polyketides belonging to diverse structural classes, including monomeric/dimeric tetrahydroxanthones and resorcylic acid lactones, were isolated from an organic extract of a fungal culture Setophoma terrestris (MSX45109) by bioactivity-directed fractionation as part of a search for anticancer leads from filamentous fungi. Of these, six were new: penicillixanthone B ( 5), blennolide H ( 6), 11-deoxyblennolide D ( 7), blennolide I ( 9), blennolide J ( 10), and pyrenomycin ( 16). The known compounds were: secalonic acid A ( 1), secalonic acid E ( 2), secalonic acid G ( 3), penicillixanthone A ( 4), paecilin B ( 8), aigialomycin A ( 11), hypothemycin ( 12), dihydrohypothemycin ( 13), pyrenochaetic acid C ( 14), and nidulalin B ( 15). The structures were elucidated by a set of spectroscopic and spectrometric techniques: the absolute configurations of compounds 1- 10 were determined by ECD spectroscopy combined with time-dependent density functional theory (TDDFT) calculations, whereas a modified Mosher's ester method was used for compound 16. The cytotoxic activities of compounds 1- 15 against the MDA-MB-435 (melanoma) and SW-620 (colon) cancer cell lines were evaluated. Compounds 1, 4, and 12 were the most potent, with IC50 values ranging from 0.16 to 2.14 μ M. When tested against a panel of bacteria and fungi, compounds 3 and 5 showed promising activity against the Gram-positive bacterium Micrococcus luteus, with MIC values of 5 and 15 μg mL-1, respectively. [ABSTRACT FROM AUTHOR]

Sulfite oxidase deficiency is a lethal genetic disease that results from defects either in the genes encoding proteins involved in molybdenum cofactor biosynthesis or in the sulfite oxidase gene itself. Several point mutations in the sulfite oxidase gene have been identified from patients suffering from this disease worldwide. Although detailed biochemical analyses have been carried out on these mutations, no structural data could be obtained because of problems in crystallizing recombinant human and rat sulfite oxidases and the failure to done the chicken sulfite oxidase gene. We synthesized the gene for chicken sulfite oxidase de novo, working backward from the amino acid sequence of the native chicken liver enzyme by PCR amplification of a series of 72 overlapping primers. The recombinant protein displayed the characteristic absorption spectrum of sulfite oxidase and exhibited steady state and rapid kinetic parameters comparable with those of the tissue-derived enzyme. We solved the crystal structures of the wild type and the sulfite oxidase deficiency-causing R138Q (R160Q in humans) variant of recombinant chicken sulfite oxidase in the resting and sulfate-bound forms. Significant alterations in the substrate-binding pocket were detected in the structure of the mutant, and a comparison between the wild type and mutant protein revealed that the active site residue Arg-450 adopts different conformations in the presence and absence of bound sulfate. The size of the binding pocket is thereby considerably reduced, and its position relative to sulfur atom of the bound sulfate to the molybdenum. [ABSTRACT FROM AUTHOR]