Comparative metabolic profiling of Vitis amurensis and Vitis vinifera during cold acclimation

Vitis amurensis is a wild Vitis plant that can withstand extreme cold temperatures.However,the accumulation of metabolites during cold acclimation(CA)in V.amurensis remains largely unknown.In this study,plantlets of V.amurensis and V.vinifera cv.Muscat of Hamburg were treated at 4℃ for 24 and 72 h,and changes of metabolites in leaves were detected by gas chromatography coupled with time-of-flight mass spectrometry.Most of the identified metabolites,including carbohydrates,amino acids,and organic acids,accumulated in the two types of grape after CA.Galactinol,raffinose,fructose,mannose,glycine,and ascorbate were continuously induced by cold in V.amurensis,but not in Muscat of Hamburg.Twelve metabolites,including isoleucine,valine,proline,2-oxoglutarate,and putrescine,increased in V.amurensis during CA.More galactinol,ascorbate,2-oxoglutarate,and putrescine,accumulated in V.amurensis,but not in Muscat of Hamburg,during CA,which may be responsible for the excellent cold tolerance in V.amurensis.The expression levels of the genes encodingβ-amylase(BAMY),galactinol synthase(GolS),and raffinose synthase(RafS)were evaluated by quantitative reverse transcription-PCR.The expression BAMY(VIT_02s0012 g00170)and RafS(VIT_05s0077 g00840)were primarily responsible for the accumulation of maltose and raffinose,respectively.The accumulation of galactinol was attributed to different members of GolS in the two grapes.In conclusion,these results show the inherent differences in metabolites between V.amurensis and V.vinifera under CA.

Functional characterization of triterpene synthases in Cibotium barometz

Cibotium barometz(Linn.)J.Sm.,a tree fern in the Dicksoniaceae family,is an economically important industrial exported plant in China and widely used in Traditional Chinese Medicine.C.barometz produces a range of bioactive triterpenes and their metabolites.However,the biosynthetic pathway of triterpenes in C.barometz remains unknown.To clarify the origin of diverse triterpenes in C.barometz,we conducted de novo transcriptome sequencing and analysis of C.barometz rhizomes and leaves to identify the candidate genes involved in C.barometz triterpene biosynthesis.Three C.barometz triterpene synthases(CbTSs)candidate genes were obtained.All of them were highly expressed in C.barometz rhizomes,consisting of the accumulation pattern of triterpenes in C.barometz.To characterize the function of these CbTSs,we constructed a squalene-and oxidosqualene-overproducing yeast chassis by overexpressing all the enzymes in the MVA pathway under the control of GAL-regulated promoter and disrupted the GAL80 gene in Saccharomyces cerevisiae simultaneously.Heterologous expressing CbTS1,CbTS2,and CbTS3 in engineering yeast strain produced cycloartenol,dammaradiene,and diploptene,respectively.Phylogenetic analysis revealed that CbTS1 belongs to oxidosqualene cyclase,while CbTS2 and CbTS3 belong to squalene cyclase.These results decipher enzymatic mechanisms underlying the origin of diverse triterpene in C.barometz.

The ER membrane protein complex subunit Emc3 controls angiogenesis via the FZD4/WNT signaling axis

The endoplasmic reticulum(ER) membrane protein complex(EMC) regulates the synthesis and quality control of membrane proteins with multiple transmembrane domains. One of the membrane spanning subunits, EMC3, is a core member of the EMC complex that provides essential hydrophilic vestibule for substrate insertion. Here, we show that the EMC subunit Emc3 plays critical roles in the retinal vascular angiogenesis by regulating Norrin/Wnt signaling. Postnatal endothelial cell(EC)-specific deletion of Emc3 led to retarded retinal vascular development with a hyperpruned vascular network, the appearance of bluntended, aneurysm-like tip endothelial cells(ECs) with reduced numbers of filopodia and leakage of erythrocytes at the vascular front. Diminished tube formation and cell proliferation were also observed in EMC3 depleted human retinal endothelial cells(HRECs). We then discovered a critical role for EMC3 in expression of FZD4 receptor of β-catenin signaling using RNA sequencing, real-time quantitative PCR(RT-q PCR) and luciferase reporter assay. Moreover, augmentation of Wnt activity via lithium chloride(Li Cl) treatment remarkably enhanced β-catenin signaling and cell proliferation of HRECs. Additionally, Li Cl partially reversed the angiogenesis defects in Emc3-c KO mice. Our data reveal that Emc3 plays essential roles in angiogenesis through direct control of FZD4 expression and Norrin/β-catenin signaling.

Exploring the catalytic function and active sites of a novel C-glycosyltransferase from Anemarrhena asphodeloides

Anemarrhena asphodeloides is an immensely popular medicinal herb in China,which contains an abundant of mangiferin.As an important bioactive xanthone C-glycoside,mangiferin possesses a variety of pharmacological activities and is derived from the cyclization reaction of a benzophenone C-glycoside(maclurin).Biosyntheti-cally,C-glycosyltransferases are critical for the formation of benzophenone C-glycosides.However,the benzo-phenone C-glycosyltransferases from Anemarrhena asphodeloides have not been discovered.Herein,a promiscuous C-glycosyltransferase(AaCGT)was identified from Anemarrhena asphodeloides.It was able to catalyze efficiently mono-C-glycosylation of benzophenone,together with di-C-glycosylation of dihydrochalcone.It also exhibited the weak O-glycosylation or potent S-glycosylation capacities toward 12 other types of flavonoid scaffolds and a simple aromatic compound with–SH group.Homology modeling and mutagenesis experiments revealed that the glycosylation reaction of AaCGT was initiated by the conserved residue H23 as the catalytic base.Three critical residues H356,W359 and D380 were involved in the recognition of sugar donor through hydrogen-bonding interactions.In particular,the double mutant of F94W/L378M led to an unexpected enzy-matic conversion of mono-C-to di-C-glycosylation.This study highlights the important value of AaCGT as a potential biocatalyst for efficiently synthesizing high-value C-glycosides.

Colorimetric recognition of melamine in milk using novel pincer zinc complex stabilized gold nanoparticles

A convenient colorimetric approach for visual detection of melamine in raw milk was realized by using gold nanoparticles(AuNPs)stabilized by an unsymmetrical terpyridyl zinc complex with a thymine fragment at one terminal and a quaternary ammonium salt at the other.Even without pre-addition of melamine or relative additives,obvious color change from red to blue was observed by naked eye in the presence of trace amount of melamine,which was attributed to the alternation of aggregation state of AuNPs caused by the selective binding between the thymine fragment and melamine via triple hydrogenbonding interactions.Remarkably,the detection limit for melamine was as low as 2.4 ppb,providing a highly sensitive and efficient approach for the visual detection of melamine.

Recent advances in the synthesis and application of N-heterocyclic carbene-based molecular cages

N-Heterocyclic carbene(NHC)-based cages have emerged as a prominent and dynamic research area within the research field of chemistry. Leveraging the distinctive electronic and steric properties of NHC ligands, the design, synthesis, and application of these corresponding cages have garnered substantial scholarly interest. In recent years, we have witnessed the successful fabrication of diverse NHC-based cages through a range of synthetic methodologies, which hold significant potential for applications in molecular recognition and catalysis. In this review, we delve into the foundational synthetic strategies that underlie the creation of NHC-based cages, employing approaches encompassing metal–NHC chelation, coordination assembly,and covalent bonding. Additionally, we compile the diverse applications of these cages within catalytic processes and molecular recognition. Lastly, we shed light on the current limitations of synthesis and outline future trends in the development of NHCbased cages.