Glucose metabolism down‐regulates the uptake of 6‐(N‐(7‐nitrobenz‐2‐oxa‐1,3‐diazol‐4‐yl)amino)‐2‐deoxyglucose (6‐NBDG) mediated by glucose transporter 1 isoform (GLUT1): theory and simulations using the symmetric four‐state carrier model

The non‐metabolizable fluorescent glucose analogue 6‐(N‐(7‐nitrobenz‐2‐oxa‐1,3‐diazol‐4‐yl)amino)‐2‐deoxyglucose (6‐NBDG) is increasingly used to study cellular transport of glucose. Intracellular accumulation of exogenously applied 6‐NBDG is assumed to reflect concurrent gradient‐driven glucose uptake by glucose transporters (GLUTs). Here, theoretical considerations are provided that put this assumption into question. In particular, depending on the microscopic parameters of the carrier proteins, theory proves that changes in glucose transport can be accompanied by opposite changes in flow of 6‐NBDG. Simulations were carried out applying the symmetric four‐state carrier model on the GLUT1 isoform, which is the only isoform whose kinetic parameters are presently available. Results show that cellular 6‐NBDG uptake decreases with increasing rate of glucose utilization under core‐model conditions, supported by literature, namely where the transporter is assumed to work in regime of slow reorientation of the free‐carrier compared with the ligand–carrier complex. To observe an increase of 6‐NBDG uptake with increasing rate of glucose utilization, and thus interpret 6‐NBDG increase as surrogate of glucose uptake, the transporter must be assumed to operate in regime of slow ligand–carrier binding, a condition that is currently not supported by literature. Our findings suggest that the interpretation of data obtained with NBDG derivatives is presently ambiguous and should be cautious because the underlying transport kinetics are not adequately established.     

The diversion of 2‐C‐methyl‐d‐erythritol‐2,4‐cyclodiphosphate from the 2‐C‐methyl‐d‐erythritol 4‐phosphate pathway to hemiterpene glycosides mediates stress responses in Arabidopsis thaliana

2‐C‐Methyl‐d ‐erythritol‐2,4‐cyclodiphosphate (MEcDP) is an intermediate of the plastid‐localized 2‐C‐methyl‐d ‐erythritol‐4‐phosphate (MEP) pathway which supplies isoprenoid precursors for photosynthetic pigments, redox co‐factor side chains, plant volatiles, and phytohormones. The Arabidopsis hds‐3 mutant, defective in the 1‐hydroxy‐2‐methyl‐2‐(E)‐butenyl‐4‐diphosphate synthase step of the MEP pathway, accumulates its substrate MEcDP as well as the free tetraol 2‐C‐methyl‐d ‐erythritol (ME) and glucosylated ME metabolites, a metabolic diversion also occurring in wild type plants. MEcDP dephosphorylation to the free tetraol precedes glucosylation, a process which likely takes place in the cytosol. Other MEP pathway intermediates were not affected in hds‐3. Isotopic labeling, dark treatment, and inhibitor studies indicate that a second pool of MEcDP metabolically isolated from the main pathway is the source of a signal which activates salicylic acid induced defense responses before its conversion to hemiterpene glycosides. The hds‐3 mutant also showed enhanced resistance to the phloem‐feeding aphid Brevicoryne brassicae due to its constitutively activated defense response. However, this MEcDP‐mediated defense response is developmentally dependent and is repressed in emerging seedlings. MEcDP and ME exogenously applied to adult leaves mimics many of the gene induction effects seen in the hds‐3 mutant. In conclusion, we have identified a metabolic shunt from the central MEP pathway that diverts MEcDP to hemiterpene glycosides via ME, a process linked to balancing plant responses to biotic stress.     

4‐Oxo‐β‐apo‐13‐carotenone from the Cyanobacterium Anabaena cylindrica PCC 7122

Apocarotenoids are widely distributed among living organisms (bacteria, fungi, algae, plants and even animals) and have been associated with several signaling functions. These compounds are generated by the activity of carotenoid cleavage dioxygenases (CCDs), whose diversity greatly contributes to the large number of apocarotenoids that have been described so far. It is nevertheless expected that a considerable diversity of these molecules is yet to be discovered. In this work, we describe the isolation and structural elucidation of the apocarotenoid 4‐oxo‐β‐apo‐13‐carotenone from the cultured freshwater cyanobacterium Anabaena cylindrica PCC 7122, corresponding to the first report of this compound from natural sources.     

A lycopene β‐cyclase/lycopene ε‐cyclase/light‐harvesting complex‐fusion protein from the green alga Ostreococcus lucimarinus can be modified to produce α‐carotene and β‐carotene at different ratios

Biosynthesis of asymmetric carotenoids such as α‐carotene and lutein in plants and green algae involves the two enzymes lycopene β‐cyclase (LCYB) and lycopene ε‐cyclase (LCYE). The two cyclases are closely related and probably resulted from an ancient gene duplication. While in most plants investigated so far the two cyclases are encoded by separate genes, prasinophyte algae of the order Mamiellales contain a single gene encoding a fusion protein comprised of LCYB, LCYE and a C‐terminal light‐harvesting complex (LHC) domain. Here we show that the lycopene cyclase fusion protein from Ostreococcus lucimarinus catalyzed the simultaneous formation of α‐carotene and β‐carotene when heterologously expressed in Escherichia coli. The stoichiometry of the two products in E. coli could be altered by gradual truncation of the C‐terminus, suggesting that the LHC domain may be involved in modulating the relative activities of the two cyclase domains in the algae. Partial deletions of the linker region between the cyclase domains or replacement of one or both cyclase domains with the corresponding cyclases from the green alga Chlamydomonas reinhardtii resulted in pronounced shifts of the α‐carotene‐to‐β‐carotene ratio, indicating that both the relative activities of the cyclase domains and the overall structure of the fusion protein have a strong impact on the product stoichiometry. The possibility to tune the product ratio of the lycopene cyclase fusion protein from Mamiellales renders it useful for the biotechnological production of the asymmetric carotenoids α‐carotene or lutein in bacteria or fungi.     

Mutant Alleles at the Brown Locus Encoding Tyrosinase‐Related Protein‐1 (TRP‐1) Affect Proliferation of Mouse Melanocytes in Culture *

Tyrosinase related protein‐1 (TRP‐1) is a melanocyte‐specific gene product involved in eumelanin synthesis. Mutation in the Tyrp1 gene is associated with brown pelage in mouse and oculocutaneous albinism Type 3 in humans (OCA3). It has been demonstrated that TRP‐1 expresses DHICA oxidase activity in the murine system. However, its actual function in the human system is still unclear. The study was designed to determine the effects of mutation at two Typr1 alleles, namely the Tyrp1^b (brown) and Tyrp1^b‐cj (cordovan) compared with wild type Tyrp1^B (black) on melanocyte function and melanin biosynthesis. The most significant finding was that both of the Tyrp1 mutations (i.e. brown expressing a point mutation and cordovan expressing decreased amount of TRP‐1 protein) resulted in attenuation of cell proliferation rates. Neither necrosis nor apoptosis was responsible for the observed decrease in cell proliferation rates of the brown and cordovan melanocytes. Ultrastructural evaluation by electron microscopic analysis revealed that both mutations in Tyrp1 affected melanosome maturation without affecting its structure. These observations demonstrate that mutation in Tyrp1 compromised tyrosinase activity within the organelle. DOPA histochemistry revealed differences in melanosomal stages between black and brown melanocytes but not between black and cordovan melanocytes. There were no significant differences in tyrosine hydroxylase activities of tyrosinase and TRP‐1 in wild type black, brown and cordovan melanocyte cell lysates. We conclude that mutations in Tyrp1 compromise cell proliferation and melanosomal maturation in mouse melanocyte cultures.     

Functional analysis of endo‐1,4‐β‐glucanases in response to Botrytis cinerea and Pseudomonas syringae reveals their involvement in plant–pathogen interactions

Plant cell wall modification is a critical component in stress responses. Endo‐1,4‐β‐glucanases (EGs) take part in cell wall editing processes, e.g. elongation, ripening and abscission. Here we studied the infection response of Solanum lycopersicum and Arabidopsis thaliana with impaired EGs. Transgenic TomCel1 and TomCel2 tomato antisense plants challenged with Pseudomonas syringae showed higher susceptibility, callose priming and increased jasmonic acid pathway marker gene expression. These two EGs could be resistance factors and may act as negative regulators of callose deposition, probably by interfering with the defence‐signalling network. A study of a set of Arabidopsis EG T‐DNA insertion mutants challenged with P. syringae and Botrytis cinerea revealed that the lack of other EGs interferes with infection phenotype, callose deposition, expression of signalling pathway marker genes and hormonal balance. We conclude that a lack of EGs could alter plant response to pathogens by modifying the properties of the cell wall and/or interfering with signalling pathways, contributing to generate the appropriate signalling outcomes. Analysis of microarray data demonstrates that EGs are differentially expressed upon many different plant–pathogen challenges, hormone treatments and many abiotic stresses. We found some Arabidopsis EG mutants with increased tolerance to osmotic and salt stress. Our results show that impairing EGs can alter plant–pathogen interactions and may contribute to appropriate signalling outcomes in many different biotic and abiotic plant stress responses.     

A flavonoid 3‐O‐glucoside:2″‐O‐glucosyltransferase responsible for terminal modification of pollen‐specific flavonols in Arabidopsis thaliana

Flavonol 3‐O‐diglucosides with a 1→2 inter‐glycosidic linkage are representative pollen‐specific flavonols that are widely distributed in plants, but their biosynthetic genes and physiological roles are not well understood. Flavonoid analysis of four Arabidopsis floral organs (pistils, stamens, petals and calyxes) and flowers of wild‐type and male sterility 1 (ms1) mutants, which are defective in normal development of pollen and tapetum, showed that kaempferol/quercetin 3‐O‐β‐d ‐glucopyranosyl‐(1→2)‐β‐d ‐glucopyranosides accumulated in Arabidopsis pollen. Microarray data using wild‐type and ms1 mutants, gene expression patterns in various organs, and phylogenetic analysis of UDP‐glycosyltransferases (UGTs) suggest that UGT79B6 (At5g54010) is a key modification enzyme for determining pollen‐specific flavonol structure. Kaempferol and quercetin 3‐O‐glucosyl‐(1→2)‐glucosides were absent from two independent ugt79b6 knockout mutants. Transgenic ugt79b6 mutant lines transformed with the genomic UGT79B6 gene had the same flavonoid profile as wild‐type plants. Recombinant UGT79B6 protein converted kaempferol 3‐O‐glucoside to kaempferol 3‐O‐glucosyl‐(1→2)‐glucoside. UGT79B6 recognized 3‐O‐glucosylated/galactosylated anthocyanins/flavonols but not 3,5‐ or 3,7‐diglycosylated flavonoids, and prefers UDP‐glucose, indicating that UGT79B6 encodes flavonoid 3‐O‐glucoside:2″‐O‐glucosyltransferase. A UGT79B6‐GUS fusion showed that UGT79B6 was localized in tapetum cells and microspores of developing anthers.     

The Molting Biomarker Molecule Exists as 2‐Acetamido‐2‐deoxy‐gluconic Acid in Urine of Blue Crabs and Helmet Crabs

N‐Acetyl‐d ‐glucosamino‐1,5‐lactone 1 has been reported as a candidate component of the sex pheromone mixture of female blue crabs, Callinectes sapidus, since it is present in the urine of reproductive females and males detect it. Theoretically, 1 can convert to a 1,4‐lactone isomer 2 or to the corresponding carboxylic acid, 2‐acetamido‐2‐deoxygluconic acid 3 by hydrolysis in aqueous solution. In this study, we examined the biologically relevant state of equilibrium mixture of 1 , 2 , and 3 in crab urine using ESI‐MS and NMR analyses. The ESI‐MS analysis showed that the dominant form of solubilized synthetic 1 is lactone 1 and/or 2 , immediately after solubilization in deuterated water, seawater, and phosphate buffer and gradually changing to carboxylic acid 3 which becomes most predominant in phosphate buffer. The NMR analysis showed that synthetic 1 converts to other forms in deuterated water and seawater, and reaches an equilibrium mixture of at least three forms within 24 h. In contrast, 1 converts to a single state of another form in deuterated water with 35 mm phosphate buffer pH 7.6 within 24 h, which is identical to the state in urine with or without phosphate buffer. Thus, we conclude that the molting biomarker sensed by male crabs is 3 .     

The dependence of leaf senescence on the balance between 1‐aminocyclopropane‐1‐carboxylate acid synthase 1 (ACS1)‐catalysed ACC generation and nitric oxide‐associated 1 (NOS1)‐dependent NO accumulation in Arabidopsis

• Ethylene and nitric oxide (NO) act as endogenous regulators during leaf senescence. Levels of ethylene or its precursor 1‐aminocyclopropane‐1‐carboxylate acid (ACC) depend on the activity of ACC synthases (ACS), and NO production is controlled by NO‐associated 1 (NOA1). However, the integration mechanisms of ACS and NOA1 activity still need to be explored during leaf senescence.
• Here, using experimental techniques, such as physiological and molecular detection, liquid chromatography‐tandem mass spectrometry and fluorescence measurement, we investigated the relevant mechanisms.
• Our observations showed that the loss‐of‐function acs1‐1 mutant ameliorated age‐ or dark‐induced leaf senescence syndrome, such as yellowing and loss of chlorophyll, that acs1‐1 reduced ACC accumulation mainly in mature leaves and that acs1‐1‐promoted NOA1 expression and NO accumulation mainly in juvenile leaves, when compared with the wild type (WT). But the leaf senescence promoted by the NO‐deficient noa1 mutant was not involved in ACS1 expression. There was a similar sharp reduction of ACS1 and NOA1 expression with the increase in WT leaf age, and this inflection point appeared in mature leaves and coincided with the onset of leaf senescence.
• These findings suggest that NOA1‐dependent NO accumulation blocked the ACS1‐induced onset of leaf senescence, and that ACS1 activity corresponds to the onset of leaf senescence in Arabidopsis.

     

A dual role for integrin‐linked kinase and β1‐integrin in modulating cardiac aging

Cardiac performance decreases with age, which is a major risk factor for cardiovascular disease and mortality in the aging human population, but the molecular mechanisms underlying cardiac aging are still poorly understood. Investigating the role of integrin‐linked kinase (ilk) and β1‐integrin (myospheroid, mys) in Drosophila, which colocalize near cardiomyocyte contacts and Z‐bands, we find that reduced ilk or mys function prevents the typical changes of cardiac aging seen in wildtype, such as arrhythmias. In particular, the characteristic increase in cardiac arrhythmias with age is prevented in ilk and mys heterozygous flies with nearly identical genetic background, and they live longer, in line with previous findings in Caenorhabditis elegans for ilk and in Drosophila for mys. Consistent with these findings, we observed elevated β1‐integrin protein levels in old compared with young wild‐type flies, and cardiac‐specific overexpression of mys in young flies causes aging‐like heart dysfunction. Moreover, moderate cardiac‐specific knockdown of integrin‐linked kinase (ILK)/integrin pathway‐associated genes also prevented the decline in cardiac performance with age. In contrast, strong cardiac knockdown of ilk or ILK‐associated genes can severely compromise cardiac integrity, including cardiomyocyte adhesion and overall heart function. These data suggest that ilk/mys function is necessary for establishing and maintaining normal heart structure and function, and appropriate fine‐tuning of this pathway can retard the age‐dependent decline in cardiac performance and extend lifespan. Thus, ILK/integrin‐associated signaling emerges as an important and conserved genetic mechanism in longevity, and as a new means to improve age‐dependent cardiac performance, in addition to its vital role in maintaining cardiac integrity.     

Enzyme‐Free Ligation of 5′‐Phosphorylated Oligodeoxynucleotides in a DNA Nanostructure

Multicomponent reactions are difficult synthetic transformations. For DNA, there is a special opportunity to align multiple strands in a folded nanostructure, so that they are preorganized to give a specific sequence. Multistrand reactions in DNA origami structures have previously been performed using photochemical crosslinking, 1,3‐diploar cycloadditions or phosphoramidate‐forming reactions. Here we report carbodiimide‐driven phosphodiester formation in a small origami sheet that produces DNA strands up to 600 nucleotides in length in a single step. The method uses otherwise unmodified oligodeoxynucleotides with a 5′‐terminal phosphate as starting materials. Compared to an enzymatic multistrand ligation involving linear duplexes, the carbodiimide‐driven ligation gave fewer side products, as detected by gel electrophoresis. The full‐length 600mer product was successfully amplified by polymerase chain reaction.     

A New 1,5‐Dihydroxy‐4‐methoxyisoquinoline from Scolopendra subspinipes mutilans

A new isoquinoline, 1,5‐dihydroxy‐4‐methoxyisoquinoline ( 1 ), was obtained from Scolopendra subspinipes mutilans. Compound 1 showed moderate cytotoxicity on tumour cells with IC₅₀ values ranging from 13 to 26 μm against five esophageal squamous cancer cells whereas low cytotoxicity against normal human esophageal epithelial cells. Isoquinoline ring oxidized at C(1), C(4), and C(5) can enhance its cytotoxicity. In addition, compound 1 showed potent inhibitory effect (inhibition rate > 50% at 13 μm ) on cell migration in human umbilical vein endothelial cells. This article mainly studies the structure and activity of 1 , and more modification of 1 as a potential anticancer agent.