Combinatorial Mutasynthesis of Scrambled Beauvericins,Cyclooligomer Depsipeptide Cell Migration Inhibitors from Beauveria bassiana

Fungal cyclooligomer depsipeptides such as beauvericin, bassianolide, and enniatins display antibiotic, antifungal, insecticidal, broad‐spectrum cancer cell antiproliferative, and cell migration inhibitory activities. We have identified a gene encoding a novel enzyme, ketoisovalerate reductase (KIVR), which is the sole provider of D ‐hydroxyisovalerate (D ‐Hiv), a common precursor for cyclooligomer depsipeptide biosynthesis in Beauveria bassiana. KIVR and related hypothetical oxidoreductases encoded in fungal genomes are similar to ketopantoate reductases but not to D ‐hydroxycarboxylate dehydrogenases. We demonstrate that a KIVR knockout B. bassiana strain can be used for the efficient mutasynthesis of unnatural beauvericin congeners. Simultaneous feeding of precursor analogues enabled the combinatorial mutasynthesis of scrambled beauvericins, some assembled entirely from unnatural precursors. The effects of the introduced structural changes on the antiproliferative and cell migration inhibitory activities of these analogues were evaluated.     

Biochemistry and Molecular Biology of Carotenoid Biosynthesis in Chili Peppers (Capsicum spp.)

Capsicum species produce fruits that synthesize and accumulate carotenoid pigments, which are responsible for the fruits’ yellow, orange and red colors. Chili peppers have been used as an experimental model for studying the biochemical and molecular aspects of carotenoid biosynthesis. Most reports refer to the characterization of carotenoids and content determination in chili pepper fruits from different species, cultivars, varieties or genotypes. The types and levels of carotenoids differ between different chili pepper fruits, and they are also influenced by environmental conditions. Yellow-orange colors of chili pepper fruits are mainly due to the accumulation of α- and β-carotene, zeaxanthin, lutein and β-cryptoxanthin. Carotenoids such as capsanthin, capsorubin and capsanthin-5,6-epoxide confer the red colors. Chromoplasts are the sites of carotenoid pigment synthesis and storage. According to the most accepted theory, the synthesis of carotenoids in chili peppers is controlled by three loci: c1, c2 and y. Several enzymes participating in carotenoid biosynthesis in chili pepper fruits have been isolated and characterized, and the corresponding gene sequences have been reported. However, there is currently limited information on the molecular mechanisms that regulate this biosynthetic pathway. Approaches to gain more knowledge of the regulation of carotenoid biosynthesis are discussed.     

海藻糖的生物合成及相关酶系

海藻糖的生理特性和应用特性已经得到广泛的认同，微生物和酶法合成海藻糖是降低海藻糖生产成本最有效的途径，主要对海藻糖的合成方法和酶法合成海藻糖相关酶系的来源、特性进行了论述。     

Isolation of σ-(L-α-aminoadipyl)-L-cysteinyl-D-valine from culture broths by covalent chromatography

An efficient procedure for the isolation of reduced -(L-α-aminoadipyl)-L-cysteinyl-D-valine (ACV) from culture supernatants of β-lactam antibiotic-producing microorganisms is described. The method utilises covalent chromatography to isolate thiols from culture broths that have been deproteinised and undergone borohydride reduction. 2-Pyridyl disulphide activated thiopropyl Sepharose was employed batchwise to isolate the thiols present in such broths from cultures of the known ACV excreter Cephalosporium acremonium N2 and the penicillin producer Penicillium chrysogenum P2. ACV was separated from these mixtures of thiols by gel permeation chromatograhy. Reversed-phase HPLC analysis showed the ACV to be of a high purity unless isolated from a highly complex culture medium.     

Effect of culture conditions of acetic acid bacteria on cellulose biosynthesis

An attempt was made to clarify the effect of culture conditions of an acetic acid bacteria (Acetobacter xylinum) on cellulose biosynthesis using glucose as carbon source in complex medium. Synchronous culture conditions were first realised on cellulose biosynthesis by cooling the system to 4°C for 24 h. Under the synchronous conditions stepwise division of the cell and the stepwise production of cellulose were found. Furthermore, cellulose was proved to be produced when the cell number in the medium was constant.     

Metabolic costs of terpenoid accumulation in higher plants

The net value of any plant trait can be assessed by measuring the costs and benefits associated with that trait. While the other contributors to this issue examine the possible benefits of terpenoids to plants, this article explores the metabolic costs of terpenoid accumulation in plants in the light of recent advances in terpenoid biochemistry. Terpenoids are more expensive to manufacture per gram than most other primary and secondary metabolites due to their extensive chemical reduction. The enzyme costs of making terpenoids are also high since terpenoid biosynthetic enzymes are apparently not shared with other metabolic pathways. In fact, plant cells may even possess more than one set of enzymes for catalyzing the basic steps of terpenoid formation. Terpenoids are usually sequestered in complex, multicellular secretory structures, and so storage costs for these substances are also likely to be substantial. However, not all of the processes involved in terpenoid accumulation require large investments of resources. For instance, the maintenance of terpenoid pools is probably inexpensive because there is no evidence that substantial quantities of terpenes are lost as a result of metabolic turnover, volatilization, or leaching. Moreover, plants may reduce their net terpenoid costs by employing individual compounds in more than one role or by catabolizing substances that are no longer needed, although it is still unclear if such practices are widespread. These findings (and other facets of terpenoid biochemistry and physiology) are discussed in relation to the assumptions and predictions of several current theories of plant defense, including the carbonnutrient balance hypothesis, the growth-differentiation balance hypothesis, and the resource availability hypothesis.     

Sphinganine‐Like Biogenesis of (E)‐1‐Nitropentadec‐1‐ene in Termite Soldiers of the Genus Prorhinotermes

In 1974, (E)‐1‐nitropentadec‐1‐ene, a strong lipophilic contact poison of soldiers of the termite genus Prorhinotermes, was the first‐described insect‐produced nitro compound. However, its biosynthesis remained unknown. In the present study, we tested the hypothesis that (E)‐1‐nitropentadec‐1‐ene biosynthesis originates with condensation of amino acids with tetradecanoic acid. By using in vivo experiments with radiolabeled and deuterium‐labeled putative precursors, we show that (E)‐1‐nitropentadec‐1‐ene is synthesized by the soldiers from glycine or L ‐serine and tetradecanoic acid. We propose and discuss three possible biosynthetic pathways.     

Identification and Characterization of a Welwitindolinone Alkaloid Biosynthetic Gene Cluster in the Stigonematalean Cyanobacterium Hapalosiphon welwitschii

The identification of a 36 kb welwitindolinone (wel) biosynthetic gene cluster in Hapalosiphon welwitschii UTEX B1830 is reported. Characterization of the enzymes responsible for assembling the early biosynthetic intermediates geranyl pyrophosphate and 3‐((Z)‐2′‐isocyanoethenyl)indole as well as a dedicated N‐methyltransferase in the maturation of N‐methylwelwitindolinone C isothiocyanate solidified the link between the wel pathway and welwitindolinone biosynthesis. Comparative analysis of the ambiguine and welwitindolinone biosynthetic pathways in two different organisms provided insights into the origins of diverse structures within hapalindole‐type molecules.