Terpenoids have diverse structures and thus represent an important class of biologically active natural products. The structural diversity of terpenoids originates from the coupling of prenyl ...diphosphate substrates, such as isopentenyl diphosphate and dimethylallyl diphosphate. These isoprenyl diphosphates undergo canonical and sequential “head‐to‐tail” coupling catalyzed by terpene synthases, followed by modifications such as cyclization, hydroxylation, and glycosylation. In recent years, several terpene synthases that catalyze irregular “non‐head‐to‐tail” couplings to afford branched terpenoids have been identified. This minireview describes structural and mechanistic insights into these unusual coupling reactions that provide a new strategy for the structural diversification of natural products.
Irregular couplings in terpenoids: Several terpene synthases that catalyze the irregular “non‐head‐to‐tail” couplings of isoprene units to afford branched terpenoids have been identified. This review describes structural and mechanistic insight into these unusual coupling reactions that provide a new strategy for the structural diversification of natural products.
High-salt intake is a major risk factor for developing hypertension in type 2 diabetes mellitus, but its effects on glucose homeostasis are controversial. We previously found that high-salt intake ...induces severe hypertension in WBN/Kob diabetic fatty (WBKDF) rats. In the present study, we examined the effects of a high-salt intake on glucose homeostasis in WBKDF rats. Male WBKDF rats and age-matched Wistar rats at 6 weeks of age were each divided into two groups and fed either a normal-sodium (NS, 0.26%) diet or high-sodium (HS, 8%) diet for 7 weeks. Systolic blood pressure and urine volume were increased in WBKDF-HS and Wistar-HS. Body weight gain and food consumption were comparable between NS and HS in both strains. Plasma and urine glucose levels were significantly increased in WBKDF-NS but not in WBKDF-HS. HOMA-IR in WBKDF-HS was significantly lower compared with that in WBKDF-NS. The high plasma adiponectin level in WBKDF-NS compared with that in Wistar-NS was further enhanced in WBKDF-HS. Glycogen deposits and fat droplets in the livers of WBKDF-HS were reduced compared with those of WBKDF-NS. The present study demonstrated that HS intake ameliorated hyperglycemia and insulin resistance in WBKDF rats, which may be due to increased plasma levels of adiponectin.
Some enzymes annotated as squalene synthase catalyze the prenylation of carbazole‐3,4‐quinone‐containing substrates in bacterial secondary metabolism. Their reaction mechanisms remain unclear because ...of their low sequence similarity to well‐characterized aromatic substrate prenyltransferases (PTs). We determined the crystal structures of the carbazole PTs, and these revealed that the overall structure is well superposed on those of squalene synthases. In contrast, the stacking interaction between the prenyl donor and acceptor substrates resembles those observed in aromatic substrate PTs. Structural and mutational analyses suggest that the Ile and Asp residues are essential for the hydrophobic and hydrophilic interactions with the carbazole‐3,4‐quinone moiety of the prenyl acceptor, respectively, and a deprotonation mechanism of an intermediary σ‐complex involving a catalytic triad is proposed. Our results provide a structural basis for a new subclass of aromatic substrate PTs.
Carbazole prenyltransferase was found to combine the overall structure of squalene synthase and the elegant stacking interaction between prenyl diphosphate and aromatic compounds observed in the aromatic substrate prenyltransferase. Structural and mutational analyses revealed the binding and deprotonation mechanisms of the carbazole‐3,4‐quinone moiety of the prenyl acceptor.
Carquinostatin A (CQS), a potent neuroprotective substance, is a unique carbazole alkaloid with both an ortho‐quinone function and an isoprenoid moiety. We identified the entire gene cluster ...responsible for CQS biosynthesis in Streptomyces exfoliatus through heterologous production of CQS and gene deletion. Biochemical characterization of seven CQS biosynthetic gene products (CqsB1–7) established the total biosynthetic pathway of CQS. Reconstitution of CqsB1 and CqsB2 showed that the synthesis of the carbazole skeleton involves CqsB1‐catalyzed decarboxylative condensation of an α‐hydroxyl‐β‐keto acid intermediate with 3‐hydroxybutyryl‐ACP followed by CqsB2‐catalyzed oxidative cyclization. Based on crystal structures and mutagenesis‐based biochemical assays, a detailed mechanism for the unique deprotonation‐initiated cyclization catalyzed by CqsB2 is proposed. Finally, analysis of the substrate specificity of the biosynthetic enzymes led to the production of novel carbazoles.
Die glorreichen Sieben: Der gesamte Biosynthesepfad des Carbazolalkaloids Carquinostatin A (CQS) wurde durch die biochemische Charakterisierung der sieben biosynthetischen CQS‐Genprodukte CqsB1–7 aufgeklärt. Die Kristallstruktur von CqsB2, das den Cyclisierungsschritt katalysiert, liefert mechanistische Einblicke in die komplizierten Reaktionen in der enzymatischen Synthese von Carbazolen.
Study of Cubic Phase Gate II Kobayashi, Masaya; Ogawa, Hisashi; Sakaguchi, Atsushi ...
Meeting Abstracts of the Physical Society of Japan,
2018
Journal Article
The PD-1 receptor, whose deficiency in mice causes autoimmune diseases such as arthritis, is considered to be a negative regulator of activated T cells and to play a crucial role in peripheral ...tolerance. To clarify the involvement of the PD-1 system in rheumatoid arthritis (RA), we investigated PD-1 expression on synovial fluid (SF) T cells from patients with RA.
FACS analysis for PD-1 was performed on SF T cells from 44 patients with RA and 6 with osteoarthritis (OA), and also on peripheral blood (PB) T cells from 12 RA patients and 7 healthy controls. Two-color analysis of cell surface PD-1 expression and the intracellular concentration of cytokine production was used to investigate CD4+ T cells from SF of patients with RA and PB from controls.
Scarcely any PD-1 expression was detected on control PB T or OA SF T cells. In contrast, PD-1+ cells made up 20.9 +/- 8.6% (mean +/- SD) of RA SF T cells. In RA SF, PD-1 was expressed more predominantly on CD4+ T cells than on CD8+ T cells. As well as expressing CD45RO and CXCR3, CD4+ PD-1+ T cells were mostly CTLA-4 positive and CD26 negative, and were enriched in CD45RB(low) cells. Intracellular cytokine staining revealed that CD4+ PD-1+, but not CD4+ PD-1-, T cells produced interleukin 10 (IL-10), and that CD4+ PD-1+ T cells produced less IL-2 than CD4+ PD-1- T cells.
PD-1+ T cells in RA SF are enriched, and phenotypic analysis suggests that these cells constitute a unique anergic T cell subset in RA SF.
Research on a cubic phase gate III Konno, Shunya; Sakaguchi, Atsushi; Takase, Kan ...
Meeting Abstracts of the Physical Society of Japan,
2019
Journal Article
Abstract
Background
Gastric cancers (GC) after
H. pylori
eradication are difficult to diagnose even by magnifying narrow-band imaging (NBI) or blue laser imaging (BLI) endoscopy. Little is known ...with regard to non-magnifying (NM)-NBI/BLI for early GC so we examined the efficacy of NM-NBI/BLI for early GC diagnosis.
Methods
We retrospectively analyzed the images of 29 small (≤ 1 cm) intramucosal GC that had been treated with endoscopic submucosal dissection and 137 benign depressed lesions (BDLs). The brightness and shape of the GCs and BDLs by NM-NBI/BLI were assessed with ImageJ software.
Results
The NBI/BLI-index, which indicates the brightness of NBI/BLI for visualization, was significantly higher in GC than BDLs in both the
H. pylori
-infected (
P
= 0.009) and -eradicated group (
P
< 0.0001), indicating that GC exhibited brighter colors than the normal surrounding mucosa. The C-index, which refers to the circularity of the lesion, was also significantly higher in GC than BDLs in both
H. pylori
-infected (
P
= 0.006) and -eradicated cases (
P
= 0.004). Based on receiver-operating characteristic curve analysis, cutoff values for the NBI/BLI- and C-indices for GC were 1.04 and 0.58 in the
H. pylori
-infected cases, and 0.98 and 0.64 in the
H. pylori
-eradicated cases. With the reference value of the NBI/BLI-index set at ≥ 0.69 with the C-index at ≥ 0.21 in the
H. pylori
-infected and the NBI/BLI-index at ≥ 0.80 with the C-index at ≥ 0.32 in the
H. pylori
-eradicated cases, both the sensitivity and negative predictive value for early GC were 100 %. A high NBI/BLI-index tended to be associated with a wide length of the intervening part histologically in the
H. pylori
-eradicated cases (
P
= 0.09).
Conclusions
The small depressed-type early GC had brighter color and rounder shape compared to BDLs in both
H. pylori
-infected and -eradicated cases. The NBI/BLI- and C-indices calculated by the image analysis may facilitate identification of small depressed-type GC.
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