https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

In the mucosa, the immune system's T cells and B cells have position-specific phenotypes and functions that are influenced by the microbiota. These cells play pivotal parts in the maintenance of immune homeostasis by suppressing responses to harmless antigens and by enforcing the integrity of the barrier functions of the gut mucosa. Imbalances in the gut microbiota, known as dysbiosis, can trigger several immune disorders through the activity of T cells that are both near to and distant from the site of their induction. Elucidation of the mechanisms that distinguish between homeostatic and pathogenic microbiota–host interactions could identify therapeutic targets for preventing or modulating inflammatory diseases and for boosting the efficacy of cancer immunotherapy.

The microbiota in adaptive immune homeostasis and disease

▪ Abstract Plant growth retardants are applied in agronomic and horticultural crops to reduce unwanted longitudinal shoot growth without lowering plant productivity. Most growth retardants act by inhibiting gibberellin (GA) biosynthesis. To date, four different types of such inhibitors are known: (a) Onium compounds, such as chlormequat chloride, mepiquat chloride, chlorphonium, and AMO-1618, which block the cyclases copalyl-diphosphate synthase and ent-kaurene synthase involved in the early steps of GA metabolism. (b) Compounds with an N-containing heterocycle, e.g. ancymidol, flurprimidol, tetcyclacis, paclobutrazol, uniconazole-P, and inabenfide. These retardants block cytochrome P450-dependent monooxygenases, thereby inhibiting oxidation of ent-kaurene into ent-kaurenoic acid. (c) Structural mimics of 2-oxoglutaric acid, which is the co-substrate of dioxygenases that catalyze late steps of GA formation. Acylcyclohexanediones, e.g. prohexadione-Ca and trinexapac-ethyl and daminozide, block particularly...

/pdf/growth-retardants-effects-on-gibberellin-biosynthesis-and-13rt99n3qy.pdf

GROWTH RETARDANTS: Effects on Gibberellin Biosynthesis and Other Metabolic Pathways

Phytosterols, phytostanols, and their conjugates in foods: structural diversity, quantitative analysis, and health-promoting uses

Plant sterols are an essential component of the membranes of all eukaryotic organisms. They are either synthesised de novo or taken up from the environment. Their function appears to be to control membrane fluidity and permeability, although some plant sterols have a specific function in signal transduction. The phytosterols are products of the isoprenoid pathway. The dedicated pathway to sterol synthesis in photosynthetic plants occurs at the squalene stage through the activity of squalene synthetase. Although the activity of 3-hydroxymethyl-3-glutaryl coenzyme A (HGMR) is rate-limiting in the synthesis of cholesterol, this does not appear to be the case with the plant sterols. Up-regulation of HGMR appears to increase the biosynthesis of cycloartenol but not the Δ5-sterols. A decline in sterol synthesis is associated with a suppression of squalene synthetase activity, which is probably a critical point in controlling carbon flow and end-product formation. The major post-squalene biosynthetic pathway is regulated by critical rate-limiting steps such as the methylation of cycloartenol into cycloeucalenol. Little is known about the factors controlling the biosynthesis of the end-point sterol esters or stanols. The commonly consumed plant sterols are sitosterol, stigmasterol and campesterol which are predominantly supplied by vegetable oils. The oils are a rich source of the steryl esters. Less important sources of sterols are cereals, nuts and vegetables. The nutritional interest derives from the fact that the sterols have a similar structure to cholesterol, and have the capacity to lower plasma cholesterol and LDL cholesterol. Since the morbidity and mortality from cardiovascular disease have been dramatically reduced using cholesterol-lowering drugs (statins), the interest in plant sterols lies in their potential to act as a natural preventive dietary product. Stanols (saturated at C-5) occur in low amounts in the diet and are equally effective in lowering plasma cholesterol and do not cause an increase in plasma levels, unlike the sterols which can be detected in plasma.

© 2000 Society of Chemical Industry

Plant sterols: biosynthesis, biological function and their importance to human nutrition.

Cholesterol and its relatives possessing the 1,2-cyclopentanoperhydrophenanthrene ring system (Figure ​(Figure1)1) form the sterolome, which comprises a chemical library of more than 1000 natural products found in all forms of eukaryotes and some prokaryotes that serve a myriad of biological functions.1,2 The structural and stereochemical commonality of these compounds derive in large part from the action of oxidosqualene synthases (formerly cyclases) that generate the parent sterol frame. In their 1985 Nobel lecture, Brown and Goldstein stated that “cholesterol is the most highly decorated small molecule in biology”, a comment supported by the many Nobel prizes awarded to individuals who devoted a large part of their lives to research one or more aspects of the chemistry and chemical biology of sterols, their metabolites, or other isoprenoids.2,3



Figure 1

Common tetracyclic steroid frame containing the 1,2-cyclopentanoperhydrophenanthrene ring skeleton.

Biosynthesis of cholesterol and other sterols.

The side chain in plant sterols can have either a methyl or ethyl addition at carbon 24 that is absent in cholesterol. The ethyl addition is the product of two sequential methyl additions. Arabidopsis contains three genes— sterol methyltransferase 1 ( SMT1) , SMT2, and SMT3— homologous to yeast ERG6 , which is known to encode an S -adenosylmethionine‐ dependent C-24 SMT that catalyzes a single methyl addition. The SMT1 polypeptide is the most similar of these Arabidopsis homologs to yeast Erg6p. Moreover, expression of Arabidopsis SMT1 in erg6 restores SMT activity to the yeast mutant. The smt1 plants have pleiotropic defects: poor growth and fertility, sensitivity of the root to calcium, and a loss of proper embryo morphogenesis. smt1 has an altered sterol content: it accumulates cholesterol and has less C-24 alkylated sterols content. Escherichia coli extracts, obtained from a strain expressing the Arabidopsis SMT1 protein, can perform both the methyl and ethyl additions to appropriate sterol substrates, although with different kinetics. The fact that smt1 null mutants still produce alkylated sterols and that SMT1 can catalyze both alkylation steps shows that there is considerable overlap in the substrate specificity of enzymes in sterol biosynthesis. The availability of the SMT1 gene and mutant should permit the manipulation of phytosterol composition, which will help elucidate the role of sterols in animal nutrition.

/pdf/sterol-methyltransferase-1-controls-the-level-of-cholesterol-595k83jokt.pdf

STEROL METHYLTRANSFERASE 1 Controls the Level of Cholesterol in Plants

Unlike most animals, insects lack the capacity to synthesize sterols that are required in lipid biostructures, as precursors to important steroid hormones and as regulators of developmental processes. Therefore insects must acquire sterols from their diet. Hundreds of different sterols have been identified and the review starts by documenting the occurrence of sterols in different insect foods. Next we look at the various nutritional and biochemical studies that have been conducted, and organize them according to insect relatedness, which allows insect sterol use and metabolic capabilities to be viewed from an evolutionary perspective. How sterol structure influences insect feeding behavior is examined, and the fate of sterols once they have been ingested, including the processes of absorption and transport, their distribution in different tissues, and their role in reproduction, is detailed. The extent to which sterols may influence ecological outcomes is also considered, especially in phytophagous insects with known sterol metabolic constraints. Finally, mention is made of the potential use of exploiting insect sterol requirements and constraints for pest control, as well as the ability of insects to adapt to the presence of novel sterols in their diet.

Insect Sterol Nutrition and Physiology: A Global Overview

https://www.cell.com/cell-metabolism/pdf/S1550-4131(15)00005-4.pdf

Identification of Natural RORγ Ligands that Regulate the Development of Lymphoid Cells

The three types of plant prenyllipids, the chlorophylls, carotenoids and prenylquinones, are integral components of a functional photosynthetic apparatus. The functional organization of these prenyllipids within the photosynthetic membrane is far from being well understood. Our present knowledge of the functional association and partition of individual carotenoids and prenylquinones with pigment proteins is reviewed. The importance of gal actoand phospholipids for a functional integration of pigments and prenylquinones in the photosynthetic membrane is underlined by results with the new grass-herbicide sethoxydim, which inhibits glycerolipid biosynthesis and blocks the accumulation but not the biosynthesis of pigments and prenylquinones. INTRODUCTION Chlorophylls and carotenoids, the photosynthetic prenylpigments and the prenylquinone derivatives plastoquinone-g, phylloquin~ne K1, ~-tocoquinone and o(-tocopherol form the group of functional chloroplast prenyllipids which are located in the thylakoids and are needed to perform the light reactions of photosynthesis (1,2). Many aspects of biosynthesis and functions of these plastidic prenyllipids had been reviewed at preceding plant lipid symposia. This report will therefore concentrate on some recent developments which might give new insights into function or metabolism of these thylakoid components. The three chapters deal with A) chlorophylls and carotenoids, B) prenylquinones, and C) the inhibition of prenyllipid accumulation and acyllipid biosynthesis in chloroplasts by the new grass herbicide sethoxydim. A. CHLOROPHYLLS AND CAROTENOIDS In algae and higher plants it is now well documented that chlorophylls and carotenoids are quantitatively bound within the thylakoids in various ways to different chlorophyll-carotenoid pigment-proteins. By polyacrylamide gel electrophoresis (PAGE) of digitonin-digested or sodium dodecylsulfate-treated thylakoid preparations one obtains 3 types of pigment proteins (3-7):

W. David Nes

Papers

Biosynthesis of cholesterol and other sterols.

STEROL METHYLTRANSFERASE 1 Controls the Level of Cholesterol in Plants

Insect Sterol Nutrition and Physiology: A Global Overview

Identification of Natural RORγ Ligands that Regulate the Development of Lymphoid Cells

The Metabolism, Structure, and Function of Plant Lipids