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[en] The structural characterization of CalO1 is reported. The X-ray structure determination at 2.4 Å resolution of the putative orsellinic acid C3 O-methyltransferase (CalO1) involved in calicheamicin biosynthesis is reported. Comparison of CalO1 with a homology model of the functionally related calicheamicin orsellinic acid C2 O-methyltransferase (CalO6) implicates several residues that are likely to contribute to the regiospecificity of alkylation. Consistent with the proposed requirement of an acyl-carrier-protein-bound substrate, this structural study also reveals structural determinants within CalO1 that are anticipated to accommodate an association with an acyl carrier protein
[en] The Andes-endemic Barnadesioideae lineage is the oldest surviving and phylogenetically basal subfamily of the Asteraceae (Compositae), a prolific group of flowering plants with world-wide distribution (∼24,000 species) marked by a rich diversity of sesquiterpene lactones (STLs). Intriguingly, there is no evidence that members of the Barnadesioideae produce STLs, specialized metabolites thought to have contributed to the adaptive success of the Asteraceae family outside South America. The biosynthesis of STLs requires the intimate expression and functional integration of germacrene A synthase (GAS) and germacrene A oxidase (GAO) to sequentially cyclize and oxidize farnesyl diphosphate into the advanced intermediate germacrene A acid leading to diverse STLs. Our previous discovery of GAO activity conserved across all major subfamilies of Asteraceae, including the phylogenetically basal lineage of Barnadesioideae, prompted further investigation of the presence of the gateway GAS in Barnadesioideae. Herein we isolated two terpene synthases (BsGAS1/BsGAS2) from the basal Barnadesia spinosa (Barnadesioideae) that displayed robust GAS activity when reconstituted in yeast and characterized in vitro. Despite the apparent lack of STLs in the Barnadesioideae, this work unambiguously confirms the presence of GAS in the basal genera of the Asteraceae. Phylogenetic analysis reveals that the two BsGASs fall into two distinct clades of the Asteraceae's GASs, and BsGAS1 clade is only retained in the evolutionary closer Cichorioideae subfamily, implicating BsGAS2 is likely the ancestral base of most GASs found in the lineages outside the Barnadesioideae. Taken together, these results show the enzymatic capacities of GAS and GAO emerged prior to the subsequent radiation of STL-producing Asteraceae subfamilies. - Highlights: • Sesquiterpene lactones are characteristic metabolites in Asteraceae family. • Barnadesioideae is the basal lineage of all Asteraceae plants, producing sesquiterpene lactones. • Two germacrene A synthases (GASs) were identified and characterized from Barnadesia spinosa. • A phylogenetic analysis showed two sub-clades of GASs have evolved in Asteraceae. • GAS enzymes evolved prior to the divergence and global dispersal of the modern Asteraceae.
[en] The inherent non-linearity of citric acid fermentation from Aspergillus niger renders its control difficult, so there is a need to fine-tune the bioreactor performance for maximum production of citric acid in batch culture. For this, fuzzy logic is becoming a popular tool to handle non-linearity of a batch process. The present manuscript deals with fuzzy logic control of citric acid accretion by A. niger in a stirred tank reactor using blackstrap sugarcane molasses as a basal fermentation medium. The customary batches were termed as control while those under fuzzy logic were experimental. The performance of fuzzy logic control of stirred tank reactor was found to be very encouraging for enhanced production of citric acid. The comparison of kinetic parameters showed improved citrate synthase ability of experimental culture (Yp/x = 7.042 g/g). When the culture grown on 150 g/l carbohydrates was monitored for Qp, Qs and Yp/s, there was significant enhancement in these variables over the control. Specific productivity of culture (qp = 0.070 g/g cells/h) was several fold increased. The enthalpy (HD = 70.5 kJ/mol) and entropy of activation (S = -144 J/mol/K) of enzyme for citric acid biosynthesis, free energies for transition state formation and substrate binding for sucrose hydrolysis of experimental were substantially improved. (author)
[en] In this study, green synthesis of silver nanoparticles (AgNPs) and silver-montmorillonite (MMT) nanocomposites (Ag/MMT) were carried out using two local plants from Iran (Ocimum basilicum L and Teucrium Polium L). The biomolecules presenting in the plant extracts acted as the reducing and capping agents. The average size of the synthesized AgNPs, using OB and TP plant extracts were around 80 nm and 20 nm, respectively. In addition, the nanoparticle sizes were further decreased using MMT as substrate, to 70 nm and 15 nm for OB and TP plant extracts, respectively. Finally, high antibacterial efficiency against E. coli and S. aureus pathogens as well as the appropriate cytotoxicity against HEP G2 cells were observed from the biosynthesized AgNPs. The present work is eco-friendly benign and can be used for large-scale fabrication of AgNPs. (paper)
[en] Several new 1, 2, 4-triazole analogs attached to substituted phenyl pyrrole or furan 5-membered heterocycles were synthesized and screened for their antifungal activity. Compounds 5, 6-dihydro-4-oxo-5-phenyl--4ph-furo[2, 3-c] pyrrole (11) and 3-(1-methyl-2-pyrrole methyl)-4-phenyl-5-(4-chlorophenylcarbamoyl methylthio)-1, 2, 4-triazole(16) showed a prominent activity against C.albicans and S.cerevisiae.The detailed synthesis and the antifungal screening are reported. (author)
[en] In this contribution, we report synthetic strategies towards potential ligands for the study of binding differences between PhzE, the first enzyme in the biosynthesis of phenazines, and the related enzyme anthranilate synthase. The ligands were designed with the overriding goal to develop new antibiotics via downregulation of phenazine biosynthesis. Graphical abstract: .
[en] Silver nanoparticles (Ag NP) have been used for over a century for many purposes including as germicides. Unique physical, chemical and biological properties of Ag NPs make them suitable for a wide range of applications in different industries and biomedical fields. Green nanobiotechnology with synthesis of NPs using biomolecules (protein, enzyme, DNA and plant extracts) have become a rapidly developing research area. Green synthesis methods have overcome the disadvantages of traditional physical and chemical synthesis approaches, such as high cost, long time scales and toxicity. In the green route, the biomolecules act as both reducing and/or stabilizing agents to produce biocompatible NPs. Promising results on antimicrobial activity of Ag NP against several pathogenic microorganisms have been reported in literature. The growth of multiple antibiotic resistant bacteria could be inhibited by using Ag NP. This review mainly discusses the synthesis routes and characterization of biomolecules capped Ag NPs and their enhanced antimicrobial properties towards various human and plant pathogens. (topical review)