A high-density and high-confinement tokamak plasma regime for fusion energy

The tokamak approach, utilizing a toroidal magnetic field configuration to confine a hot plasma, is one of the most promising designs for developing reactors that can exploit nuclear fusion to generate electrical energy1,2. To reach the goal of an economical reactor, most tokamak reactor designs3-10 simultaneously require reaching a plasma line-averaged density above an empirical limit-the so-called Greenwald density11-and attaining an energy confinement quality better than the standard high-confinement mode12,13. However, such an operating regime has never been verified in experiments. In addition, a long-standing challenge in the high-confinement mode has been the compatibility between a high-performance core and avoiding large, transient edge perturbations that can cause very high heat loads on the plasma-facing-components in tokamaks. Here we report the demonstration of stable tokamak plasmas with a line-averaged density approximately 20% above the Greenwald density and an energy confinement quality of approximately 50% better than the standard high-confinement mode, which was realized by taking advantage of the enhanced suppression of turbulent transport granted by high density-gradients in the high-poloidal-beta scenario14,15. Furthermore, our experimental results show an integration of very low edge transient perturbations with the high normalized density and confinement core. The operating regime we report supports some critical requirements in many fusion reactor designs all over the world and opens a potential avenue to an operating point for producing economically attractive fusion energy.

Site-specific crosslinking and assembly of tetrameric β-glucuronidase improve glycyrrhizin hydrolysis

In this study, eight nonconserved residues with exposed surfaces and flexible conformations of the homotetrameric PGUS (β-glucuronidase from Aspergillus oryzae Li-3) were identified. Single-point mutation into cysteine enabled the thiol-maleimide reaction and site-specific protein assembly using a two-arm polyethylene glycol (PEG)-maleimide crosslinker (Mal2 ). The Mal2 (1k) (with 1 kDa PEG spacer)-crosslinked PGUS assemblies showed low crosslinking efficiency and unimproved thermostability except for G194C-Mal2 (1k). To improve the crosslinking efficiency, a lengthened crosslinker Mal2 (2k) (with 2 kDa PEG spacer) was used to produce PGUS assembly and a highly improved thermostability was achieved with a half-life of 47.2-169.2 min at 70°C, which is 1.04-3.74 times that of wild type PGUS. It is found that the thermostability of PGUS assembly was closely associated with the formation of inter-tetramer assembly and intratetramer crosslinking, rather than the PEGylation of the enzyme. Therefore, the four-arm PEG-maleimide crosslinker Mal4 (2k) (with 2 kDa PEG spacer) was employed to simultaneously increase the inter-tetramer assembly and intratetramer crosslinking, and the resulting PGUS assemblies showed further improved thermostabilities compared with Mal2 (2k)-crosslinked assemblies. Finally, the application of PGUS assemblies with significantly improved thermostability to the bioconversion of GL proved that the PGUS assembly is a strong catalyst for glycyrrhizin (GL) hydrolysis in industrial applications.

Strategies for modulating transglycosylation activity, substrate specificity, and product polymerization degree of engineered transglycosylases

Glycosides are widely used in many fields due to their favorable biological activity. The traditional plant extractions and chemical methods for glycosides production are limited by environmentally unfriendly, laborious protecting group strategies and low yields. Alternatively, enzymatic glycosylation has drawn special attention due to its mild reaction conditions, high catalytic efficiency, and specific stereo-/regioselectivity. Glycosyltransferases (GTs) and retaining glycoside hydrolases (rGHs) are two major enzymes for the formation of glycosidic linkages. Therein GTs generally use nucleotide phosphate activated donors. In contrast, GHs can use broader simple and affordable glycosyl donors, showing great potential in industrial applications. However, most rGHs mainly show hydrolysis activity and only a few rGHs, namely non-Leloir transglycosylases (TGs), innately present strong transglycosylation activities. To address this problem, various strategies have recently been developed to successfully tailor rGHs to alleviate their hydrolysis activity and obtain the engineered TGs. This review summarizes the current modification strategies in TGs engineering, with a special focus on transglycosylation activity enhancement, substrate specificity modulation, and product polymerization degree distribution, which provides a reference for exploiting the transglycosylation potentials of rGHs.

Experimental Validation of a Kinetic Ballooning Mode in High-Performance High-Bootstrap Current Fraction Fusion Plasmas

We report the observation of a set of coherent high frequency electromagnetic fluctuations that leads to a turbulence induced self-regulating phenomenon in the DIII-D high bootstrap current fraction plasma. The fluctuations have frequency of 130-220  kHz, the poloidal wavelength and phase velocity are 16-30  m^{-1} and ∼30  km/s, respectively, in the outboard midplane with the estimated toroidal mode number n∼5-9. The fluctuations are located in the internal transport barrier (ITB) region at large radius and are experimentally validated to be kinetic ballooning modes (KBM). Quasilinear estimation predicts the KBM to be able to drive experimental particle flux and non-negligible thermal flux, suggesting its significant role in regulating the ITB saturation.

Action of the plant-based essential oil-derived compound Taxol for improvising drought tolerance in Eucalyptus by modulating the VIT1 channel protein: a cutting-edge computational approach

Background: Drought poses a significant threat to the growth and survival of woody plants, especially Eucalyptus grandis, which is known for its slow and steady growth. Understanding the physiological and molecular responses of E. grandis to abiotic stress is essential for developing strategies to improve its drought resistance. This study focuses on the potential vulnerability of E. grandis during the initial months of root system proliferation and investigates the role of the essential oil-derived compound Taxol in enhancing its drought resistance. Methodology: A comprehensive analysis was performed on various aspects of E. grandis, including morphological features, photosynthetic rates, pigment concentrations, nitrogenous components, and lipid peroxidation. Furthermore, the study examined the accumulation of soluble carbohydrates, proline, and antioxidant enzymes as part of the tree's response to drought stress. Molecular docking and molecular dynamics simulations were conducted to determine the binding affinity of Taxol, an essential oil derived from Taxus brevifolia, with the VIT1 protein in E. grandis. Results: E. grandis displayed remarkable resilience to drought by accumulating vast reserves of soluble carbohydrates, proline, and antioxidant enzymes. The essential oil-derived compound Taxol exhibited a strong binding affinity with the VIT1 protein (-10.23 kcal/mol), suggesting its potential role in enhancing the tree's drought resistance. Conclusion: This study reveals the pivotal role of Taxol in augmenting the resilience of E. grandis against drought stress and improving its therapeutic oil properties. Emphasizing the tree's inherent tolerance during its susceptible early stages is crucial in promoting sustainable agriculture and forestry practices. The findings underscore the importance of advanced scientific research in uncovering the concealed capabilities of robust trees like E. grandis as we continue our pursuit of a sustainable future.

Development and validation of nomograms for predicting the risk probability of carbapenem resistance and 28-day all-cause mortality in gram-negative bacteremia among patients with hematological diseases

Objectives

Gram-negative bacteria (GNB) bloodstream infections (BSIs) are the most widespread and serious complications in hospitalized patients with hematological diseases. The emergence and prevalence of carbapenem-resistant (CR) pathogens has developed into a considerable challenge in clinical practice. Currently, nomograms have been extensively applied in the field of medicine to facilitate clinical diagnosis and treatment. The purpose of this study was to explore risk indicators predicting mortality and carbapenem resistance in hematological (HM) patients with GNB BSI and to construct two nomograms to achieve personalized prediction.

Methods

A single-center retrospective case-control study enrolled 244 hospitalized HM patients with GNB-BSI from January 2015 to December 2019. The least absolute shrinkage and selection operator (LASSO) regression analysis and multivariate logistic regression analysis were conducted to select potential characteristic predictors of plotting nomograms. Subsequently, to evaluate the prediction performance of the models, the prediction models were internally validated using the bootstrap approach (resampling = 1000) and 10-fold cross validation.

Results

Of all 244 eligible patients with BSI attributed to GNB in this study, 77 (31.6%) were resistant to carbapenems. The rate of carbapenem resistance exhibited a growing tendency year by year, from 20.4% in 2015 to 42.6% in 2019 (p = 0.004). The carbapenem resistance nomogram constructed with the parameters of hypoproteinemia, duration of neutropenia ≥ 6 days, previous exposure to carbapenems, and previous exposure to cephalosporin/β-lactamase inhibitors indicated a favorable discrimination ability with a modified concordance index (C-index) of 0.788 and 0.781 in both the bootstrapping and 10-fold cross validation procedures. The 28-day all-cause mortality was 28.3% (68/240). The prognosis nomogram plotted with the variables of hypoproteinemia, septic shock, isolation of CR-GNB, and the incomplete remission status of underlying diseases showed a superior discriminative ability of poorer clinical prognosis. The modified C-index of the prognosis nomogram was 0.873 with bootstrapping and 0.887 with 10-fold cross validation. The decision curve analysis (DCA) for two nomogram models both demonstrated better clinical practicality.

Conclusions

For clinicians, nomogram models were effective individualized risk prediction tools to facilitate the early identification of HM patients with GNB BSI at high risk of mortality and carbapenem resistance.

Pre-transplant CRP-albumin ratio as a biomarker in patients receiving haploidentical allogeneic hematopoietic transplantation: Developing a novel DRCI-based nomogram

Background

In allogeneic hematopoietic stem cell transplantation (allo-HSCT), prognostic indicators effectively predict survival. The Disease conditions prior to transplantation dramatically affects the outcome of HSCT. Optimization of the pre-transplant risk assessment is critical for enhancing allo-HSCT decision-making. Inflammation and nutritional status play significant roles in cancer genesis and progression. As a combined inflammatory and nutritional status biomarker, the C-reactive protein/albumin ratio (CAR) can accurately forecast the prognosis in various malignancies. This research sought to examine the predictive value of CAR and develop a novel nomogram by combining biomarkers and evaluating their importance following HSCT.

Methods

Analyses were conducted retroactively on a cohort of 185 consecutive patients who underwent haploidentical hematopoietic stem cell transplantation (haplo-HSCT) at Wuhan Union Medical College Hospital during the period from February 2017 to January 2019. Of these patients, 129 were randomly assigned to the training cohort, and the remaining 56 patients constituted the internal validation cohort. Univariate and multivariate analyses were carried out to examine the predictive significance of clinicopathological factors in the training cohort. Subsequently, the survival nomogram model was developed and compared with the disease risk comorbidity index (DRCI) using the concordance index (C-index), calibration curve, receiver operating characteristics (ROC) curve, and decision curve analysis (DCA).

Results

Patients were separated into low and high CAR groups using a cutoff of 0.087, which independently predicted overall survival (OS). Based on risk factors, CAR, the Disease Risk Index(DRI), and the Hematopoietic Cell Transplantation-specific Comorbidity Index(HCT-CI), the nomogram was developed to predict OS. The C-index and area under the ROC curve confirmed the improved predictive accuracy of the nomogram. The calibration curves revealed that the observed probabilities agreed well with those predicted by the nomogram in training, validation and entire cohort. It was confirmed by DCA that the nomogram offered greater net benefits than DRCI among all cohorts.

Conclusion

CAR is an independent prognostic indicator for haplo-HSCT outcomes. Higher CAR was related to worse clinicopathologic characteristics and poorer prognoses in patients underwent haplo-HSCT. This research provided an accurate nomogram for predicting the OS of patients following haplo-HSCT, illustrating its potential clinical utility.

Corrigendum: Pre-transplant CRP-albumin ratio as a biomarker in patients receiving haploidentical allogeneic hematopoietic transplantation: developing a novel DRCI-based nomogram

[This corrects the article DOI: 10.3389/fimmu.2023.1128982.].

Characterization of the complete chloroplast genome of Euphorbia pekinensis Rupr. (Euphorbiaceae)

Euphorbia pekinensis Rupr. 1859 is a medicinal herb endemic to China and distributed throughout the country, particularly across the northern part of the mainland. However, the systematic classification of Euphorbiaceae remains controversial. Therefore, studying the chloroplast genome of E. pekinensis is crucial for the resolution of this taxonomic dispute, clarification of the systematic status of Euphorbia, and establishment of an accurate classification system for Euphorbiaceae. In this study, we sequenced the complete chloroplast genome of E. pekinensis using Illumina sequencing technology and annotated it using GeSeq. The complete chloroplast genome was 162,002-bp-long with a guanine–cytosine (GC) content of 35.7%. It included one large single-copy (LSC), one small single-copy (SSC), and two inverted repeat sequence regions (IRa and IRb), which were 90,225 bp, 18,067 bp, and 26,855 bp in length, respectively, and are indicative of a typical tetrad structure. The genome encoded 129 functional genes, comprising 85 protein-coding genes, 36 tRNA genes, and eight rRNA genes. According to the maximum-likelihood phylogenetic tree that was constructed using 16 complete chloroplast genomes, E. pekinensis was found to be closely related to E. ebracteolata. Therefore, the complete chloroplast genome of E. pekinensis provides a better understanding of Euphorbia genetics.

A transposon insertion drove the loss of natural seed shattering during foxtail millet domestication

Loss of seed shattering was a key step during cereal domestication, and it greatly facilitated seed harvest of the staple cereal foxtail millet (Setaria italica) because the cereal has very small seeds. However, the genetic basis for this loss has been largely unknown. Here, we combined comparative and association mapping to identify an 855-bp Harbinger transposable element insertion in the second exon of the foxtail millet gene shattering1 (sh1) that was responsible for the loss of seed shattering. The sh1 gene encodes zinc finger and YABBY domains. The insert prevents transcription of the second exon, causing partial loss of the zinc finger domain and then loss of natural seed shattering. Specifically, sh1 functions as a transcription repressor and represses the transcription of genes associated with lignin synthesis in the abscission zone, including CAD2. The diversity of sh1 is highly reduced in foxtail millet, consistent with either a severe domestication bottleneck or a selective sweep. Phylogenetic analysis of sh1 further revealed a single origin of foxtail millet in China. Our results support the theories that transposons were the most active factors in genome evolution driving loss of natural seed shattering during foxtail millet domestication and that sh1 underwent parallel selection during domestication across different cereal species.

Gene duplication drove the loss of awn in sorghum

Loss of the awn in some cereals, including sorghum, is a key transition during cereal domestication or improvement that has facilitated grain harvest and storage. The genetic basis of awn loss in sorghum during domestication or improvement remains unknown. Here, we identified the awn1 gene encoding a transcription factor with the ALOG domain that is responsible for awn loss during sorghum domestication or improvement. awn1 arose from a gene duplication on chromosome 10 that translocated to chromosome 3, recruiting a new promoter from the neighboring intergenic region filled with "noncoding DNA" and recreating the first exon and intron. awn1 acquired high expression after duplication and represses the elongation of awns in domesticated sorghum. Comparative mapping revealed high collinearity at the awn1 paralog locus on chromosome 10 across cereals, and awn growth and development were successfully reactivated on the rice spikelet by inactivating the rice awn1 ortholog. RNA-seq and DAP-seq revealed that as a transcriptional repressor, AWN1 bound directly to a motif in the regulatory regions of three MADS genes related to flower development and two genes, DL and LKS2, involved in awn development. AWN1 downregulates the expression of these genes, thereby repressing awn elongation. The preexistence of regulatory elements in the neighboring intergenic region of awn1 before domestication implicates that noncoding DNA may serve as a treasure trove for evolution during sorghum adaptation to a changing world. Taken together, our results suggest that gene duplication can rapidly drive the evolution of gene regulatory networks in plants.

Multiscale Chirping Modes Driven by Thermal Ions in a Plasma with Reactor-Relevant Ion Temperature

A thermal ion driven bursting instability with rapid frequency chirping, considered as an Alfvénic ion temperature gradient mode, has been observed in plasmas having reactor-relevant temperature in the DIII-D tokamak. The modes are excited over a wide spatial range from macroscopic device size to microturbulence size and the perturbation energy propagates across multiple spatial scales. The radial mode structure is able to expand from local to global in ∼0.1  ms and it causes magnetic topology changes in the plasma edge, which can lead to a minor disruption event. Since the mode is typically observed in the high ion temperature ≳10  keV and high-β plasma regime, the manifestation of the mode in future reactors should be studied with development of mitigation strategies, if needed. This is the first observation of destabilization of the Alfvén continuum caused by the compressibility of ions with reactor-relevant ion temperature.

Underestimated heavy metal pollution of the Minjiang River, SE China: Evidence from spatial and seasonal monitoring of suspended-load sediments

Previous assessments on rivers in SE China with highly developed economy and enormous population indicate diverse and relatively low particulate heavy metal pollution levels. However, the controlling mechanisms for heavy metal enrichment and transport remain enigmatic. Here, we target a mesoscale mountainous river, the Minjiang River, and obtain grain size, mineralogical and heavy metal concentration (Pb, Cd, Cr, Mn, Mo, Zn, V, Co, Ni, Cu) data from seasonal suspended particulate matter (SPM) near the river mouth, riverbed sediments and SPM samples from mainstream and major tributaries of the river. The results indicate that SPM samples have higher particulate heavy metal concentrations than riverbed sediments collected in pairs. Heavy metal concentrations of Cd, Zn, Cr, V, Co, Ni and Cu are higher in upstream SPM samples than those in downstream regions, whereas Pb, Mn and Mo concentrations don't show this spatial variation. Most heavy metals (e.g., Pb and Zn) show high concentrations in flood seasons and relatively low concentrations in dry seasons, revealing a hydrologic control. However, Cr and Mn show high concentrations in some dry season samples, suggesting incidental anthropogenic input events. The SPM-based pollution assessments using enrichment factor, geoaccumulation index and potential ecological risk index demonstrate that the Minjiang River is moderately to strongly polluted by particulate Pb, Cd, Mo and Zn contaminations and most particulate heavy metals have moderate to considerable potential ecological risks. We contend that transport and discharge of particulate heavy metals by the Minjiang River are controlled by both natural and anthropogenic forcings and the pollution levels are worse than previously known. Our findings suggest that particulate heavy metal discharge by subtropical mountainous rivers is related to sediment types and hydrologic characteristics. Therefore, high-spatiotemporal-resolution investigations on river SPM samples are highly recommended to better evaluate particulate heavy metal pollution levels and aquatic environmental conditions.

LncRNA ROR1-AS1 promotes colon cancer cell proliferation by suppressing the expression of DUSP5/CDKN1A

OBJECTIVE

The purpose of this study was to explore the possible role of ROR1-AS1 in the pathogenesis of colon cancer and the underlying mechanism.

PATIENTS AND METHODS

The expression levels of ROR1-AS1 in 75 colon cancer tissue samples and adjacent ones, as well as in cell lines were examined by quantitative Polymerase Chain Reaction (qPCR). Then, ROR1-AS1 overexpression plasmid and siRNA were transfected into colon cancer cells using liposome method. After that, Cell Counting Kit-8 (CCK-8) and plate colony formation assays were conducted to analyze cell proliferation, while flow cytometry was applied for the analysis of cell cycle and apoptosis. At last, the mechanism of action of ROR1-AS1 was further explored by nuclear separation, RNA binding protein immunoprecipitation (RIP) and chromatin immunoprecipitation (CHIP) assays.

RESULTS

ROR1-AS1 level in colon cancer tissues was remarkably higher than that in normal tissues, and the expression in tumors of stage III and IV was remarkably higher than those of stage I and II. Meanwhile, tumors with diameters more than 5 cm had a higher ROR1-AS1 expression than those less than 5 cm. After transfection with ROR1-AS1 overexpression plasmid, the cell proliferation ability was enhanced, the G0/G1 phase time of cell cycle was shortened, and the apoptosis was suppressed. However, the opposite result was observed after ROR1-AS1 was downregulated. Furthermore, RIP showed that ROR1-AS1 can bind to enhancer of zeste homolog 2 (EZH2) and inhibit the expression of DUSP5, and thus be engaged in the proliferation and apoptosis of colon cancer cells.

CONCLUSIONS

ROR1-AS1 is highly expressed either in colon cancer tissues or in cell lines, which is able to enhance cell proliferation, accelerate cell cycle, and inhibit cell apoptosis. The mechanism of ROR1-AS1 to participate in the development of colon cancer may be the downregulation of DUSP5 via combination with EZH2.

Isolation and characterization of ergosterol from Monascus anka for anti-lipid peroxidation properties

Unbalanced lipid peroxidation damages the human body, and is associated with the formation of tumors, infections, inflammations, autoimmune diseases, and cardiovascular and cerebrovascular diseases. However, food and drugs that contain anti-lipid peroxidation active substances, can help to protect against these negative health impacts. We observed lipid peroxidation inhibition in the metabolites of fermented Monascus anka, in media with Dendrobium nobile Lindl. The anti-lipid peroxidation ability of the extracts was strongest in ethyl acetate, so this was selected for further purifications. A crystal with strong antioxidant properties was obtained by column chromatography. Based on its spectroscopic analysis by Electron Bombardment Ion Source and Mass Spectrometry (EI-MS), ¹H-Nuclear Magnetic Resonance (¹H-NMR), and ¹³C-Nuclear Magnetic Resonance (¹³C-NMR), the isolated crystal was identified as ergosterol. The inhibition rates of the lipid peroxide due to the ergosterol were 57.42%, at 2μg/mL in vitro. Simultaneously, the survival rates of the damaged cells treated with 0.3mmol/L H₂O₂ were significantly improved with the ergosterol, up to 43.88% (200μg/mL) and 46.64% (400μg/mL), compared to 36.47% for the injured cells. The survival rate of the cells was 78.32% (400μg/mL), with ergosterol as a prevention. Cell injury can increase the level of intracellular ROS, but its levels in the damaged cells were reduced after the ergosterol treatments, and the reduction increased with the increasing concentrations. A 400μg/mL concentration resulted in the lowest fluorescence intensity; 33421.11 AU below the normal level. Ergosterol significantly reduced the ROS levels, to reduce the cell damage. Ergosterol from Monascus anka was thus found to have strong anti-lipid peroxidation and antioxidant capabilities, and the ability to protect and repair damaged cells. It may consequently serve as a potential natural antioxidant and will play an important role in human anti-lipid peroxide.

LINC01605 promotes the proliferation of laryngeal squamous cell carcinoma through targeting miR-493-3p

OBJECTIVE

The purpose of this study was to elucidate the potential influence of LINC01605 on the progression of laryngeal squamous cell carcinoma (LSCC) and the underlying mechanism.

PATIENTS AND METHODS

LINC01605 and microRNA-493-3p (miR-493-3p) levels in normal laryngeal tissues, LSCC tissues, and paired paracancerous tissues were detected. Regulatory effects of LINC01605 on proliferative ability and apoptosis in HEp-2 and AMC-HN-8 cells were assessed. Besides, the interaction between LINC01605 and miR-493-3p was evaluated by Dual-Luciferase reporter gene assay and Spearman's rank correlation analysis. Finally, rescue experiments were conducted to clarify the role of LINC01605/miR-493-3p axis in the progression of LSCC.

RESULTS

LINC01605 was upregulated and miR-493-3p was downregulated in LSCC tissues. Knockdown of LINC01605 inhibited proliferative ability, and stimulated apoptosis in HEp-2 and AMC-HN-8 cells. Moreover, LINC01605 directly bound to miR-493-3p, and the former negatively regulated the level of the latter. In addition, miR-493-3p was able to reverse the regulatory effect of LINC01605 on proliferative ability in LSCC.

CONCLUSIONS

LINC01605 is upregulated in LSCC tissues, and it promotes the malignant progression of LSCC via targeting miR-493-3p.

Role of Microtearing Turbulence in DIII-D High Bootstrap Current Fraction Plasmas

We report on the first direct comparisons of microtearing turbulence simulations to experimental measurements in a representative high bootstrap current fraction (f_{BS}) plasma. Previous studies of high f_{BS} plasmas carried out in DIII-D with large radius internal transport barriers (ITBs) have found that, while the ion energy transport is accurately reproduced by neoclassical theory, the electron transport remains anomalous and not well described by existing quasilinear transport models. A key feature of these plasmas is the large value of the normalized pressure gradient, which is shown to completely stabilize conventional drift-wave and kinetic ballooning mode instabilities in the ITB, but destabilizes the microtearing mode. Nonlinear gyrokinetic simulations of the ITB region performed with the cgyro code demonstrate that the microtearing modes are robustly unstable and capable of driving electron energy transport levels comparable to experimental levels for input parameters consistent with the experimental measurements. These simulations uniformly predict that the microtearing mode fluctuation and flux spectra extend to significantly shorter wavelengths than the range of linear instability, representing significantly different nonlinear dynamics and saturation mechanisms than conventional drift-wave turbulence, which is also consistent with the fundamental tearing nature of the instability. The predicted transport levels are found to be most sensitive to the magnetic shear, rather than the temperature gradients more typically identified as driving turbulent plasma transport.

Turbulent lithosphere deformation in the Tibetan Plateau

In this work, we show that the Tibetan Plateau deformation demonstrates turbulence-like statistics, e.g., spatial invariance across continuous scales. A dual-power-law behavior is evident to show the existence of two possible conservation laws for the enstrophy-like cascade in the range 500≲r≲2000km and kinetic-energy-like cascade in the range 50≲r≲500km. The measured second-order structure-function scaling exponents ζ(2) are similar to their counterparts in the Fourier scaling exponents observed in the atmosphere, where in the latter case the earth's rotation is relevant. The turbulent statistics observed here for nearly zero-Reynolds-number flow can be interpreted by the geostrophic turbulence theory. Moreover, the intermittency correction is recognized with an intensity close to that of the hydrodynamic turbulence of high-Reynolds-number turbulent flows, implying a universal scaling feature of very different turbulent flows. Our results not only shed new light on the debate regarding the mechanism of the Tibetan Plateau deformation but also lead to new challenges for the geodynamic modeling using Newton or non-Newtonian models because the observed turbulence-like features have to be taken into account.

Breast cancer Ki67 expression prediction by DCE-MRI radiomics features

AIM

To investigate whether quantitative radiomics features extracted from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) are associated with Ki67 expression of breast cancer.

MATERIALS AND METHODS

This institutional review board-approved retrospective study comprised 377 Chinese women who were diagnosed with invasive breast cancer in 2015. This cohort included 53 low-Ki67 expression (Ki67 proliferation index less than 14%) and 324 cases with high-Ki67 expression (Ki67 proliferation index more than 14%). A binary-classification of low-versus high- Ki67 expression was performed. A set of 56 quantitative radiomics features, including morphological, greyscale statistic, and texture features, were extracted from the segmented lesion area. Three machine learning classification methods, including naive Bayes, k-nearest neighbour and support vector machine, were employed for the classification and the least absolute shrink age and selection operator (LASSO) method was used to select most predictive features set for the classifiers. Classification performance was evaluated by the area under receiver operating characteristic curve (AUC), accuracy, sensitivity, and specificity.

RESULES

The model that used naive Bayes classification method achieved the best performance than the other two methods, yielding 0.773 AUC, 0.757 accuracy, 0.777 sensitivity and 0.769 specificity. Three most predictive features, i.e., contrast, entropy and line likeness, were selected by the LASSO method and showed a statistical significance (p<0.05) in the classification.

CONCLUSION

The present study showed that quantitative radiomics imaging features of breast tumour extracted from DCE-MRI are associated with breast cancer Ki67 expression. Future larger studies are needed in order to further evaluate the findings.

The effects of a sodium-glucose cotransporter 2 inhibitor on diabetic nephropathy and serum oxidized low-density lipoprotein levels

OBJECTIVE

To investigate the effect of an SGLT-2 inhibitor on diabetic nephropathy and serum oxidized low-density lipoprotein (ox-LDL) levels.

PATIENTS AND METHODS

We randomly divided 126 patients with diabetic nephropathy into the treatment group and control group. The 63 patients in the treatment group received an SGLT-2 inhibitor in addition to routine insulin therapy, while the control group received only insulin to control blood glucose. All laboratory indexes were recorded before and after treatment with the SGLT-2 inhibitor. The prognosis of patients was followed-up. Simultaneously, 63 healthy and BMI-matched in-patients were selected as the healthy control group. Peripheral blood samples were collected from all groups, and the levels of ROS were measured by ELISA.

RESULTS

Renal function indexes such as urinary protein, creatinine, blood urea nitrogen, and glomerular filtration rate (GFR) were significantly higher with SGLT-2 inhibitor treatment compared with the control group (p<0.05). The fasting blood glucose level was not significantly increased before or after treatment (p>0.05). The levels of ROS in peripheral blood were significantly lower in the treatment group than in the control group (p<0.05). Observation at the 1-year follow-up showed that the average GFR was significantly higher in the treatment group than in the control group. Furthermore, the proportion of patients with stage 1-3 chronic kidney disease was significantly higher in the treatment group than in the control group (p<0.05).

CONCLUSIONS

The SGLT-2 inhibitor had a good therapeutic effect on renal function in patients with diabetic nephropathy, without having effects on fasting blood glucose. Additionally, it significantly delayed the progression of nephropathy. It is therefore worth clinical promotion.

Nonisothermal crystallization kinetics of polyphenylene sulfide composites based on organic clay modified by benzimidazolium salt

Polyphenylene sulfide (PPS)/organic clay nanocomposites were prepared by simple melt blending. A synthesized benzimidazolium salt was used to modify the sodium montmorillonite in order to improve the compatibility with the PPS. The nonisothermal crystallization kinetics of PPS/organic clay composites were investigated by differerntial scanning calorimetry(DSC). It was observed that the crystallization peak temperature of PPS/organic clay composites was higher than pure PPS at various cooling rates. Several models such as the Ozawa and Mo equation were used to characterize the nonisothermal cooling crystallization kinetics of the PPS/organic clay composites. The results indicated that the Ozawa equation was not successful, while the Mo equation was successful to describe the nanoisothermal ctystallization kinetics of PPS/organic clay nanocomposites. The results also indicated that organic clay not only served as heterogeneous nucleating agents for PPS crystallization at lower content but also restricted the mobility and diffusion of PPS chains at higher content. These results were further supported by the crystallization activation energy of the samples determined by the Kissinger method.

[Distribution characteristics of soil carbon and nitrogen in different land use types changed from urban wetlands.]

Five land use types of Longzihu wetland in Bengbu City, Anhui Province of China, including woodland, greenbelt, aquaculture land, cultivated land, shelter forest, were chosen as the research object. Through analyzing the content and allocation proportion of total organic carbon (TOC), total nitrogen (TN), particulate organic carbon (POC), particulate organic nitrogen (PON), as well as soil carbon nitrogen ratio (C/N) and soil particles component carbon nitrogen ratio (POC/TOC), soil carbon and nitrogen distribution characteristics were discussed under dif-ferent human disturbance intensities and modes. Results showed that TOC showed surface accumulation in woodland, aquaculture land and cultivated land, while it did not show significant variation in each soil layer of greenbelt and shelter forest. POC, TN and PON showed surface accumulation in all land utilization types. Greenbelt and shelter forest, being disturbed strongly by human activities, had higher POC allocation proportions, while aquaculture land and cultivated land, heavily interfered by human activities, had relatively lower POC allocation proportions which were commensurate with that of woodland. Woodland received less interference by human activities, so in addition to disturbance intensity, disturbance mode might be another important factor affecting POC allocation proportion. C/N decreased with the increase of soil depth in woodland, but C/N of greenbelt, cultivated land and shelter forest had no obvious changes along the soil profile. Soil depth had no significant impact on POC/TOC in the land use types except woodland and cultivated land.

Modification of montmorillonite by different surfactants and its use for the preparation of polyphenylene sulfide nanocomposites

Polyphenylene sulfide (PPS)/clay composites were prepared by simple melt blending. Three different kinds of surfactants such as cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl benzene sulfonate (SDBS), and synthetic 1,3-dihexadecyl-3H-benzimidazolium bromide (Bz) were used as organic modifiers for the organic modification process. The benzimidazolium-modified montmorillonite (Bz-MMT) and CTAB-modified MMT (CTAB-MMT) exhibited larger interlayer spacing than SDBS-modified MMT (SDBS-MMT), while SDBS-MMT and Bz-MMT exhibited higher thermal stability compared with the CTAB-MMT. The morphology of the PPS/organic MMT nanocomposites was evaluated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The nanocomposites based on SDBS-MMT and Bz-MMT exhibited good overall dispersion of organic MMT with a mixed dispersion of intercalated and exfoliated structures. Differential scanning calorimetry and thermogravimetric analysis (TGA) were used to evaluate the thermal properties of PPS/organic MMT nanocomposites. The crystallization process of PPS in all nanocomposites was accelerated, and the crystallinity also increased, when compared with the pure PPS from the DSC analysis. The TGA analysis indicated that nanocomposites based on SDBS-MMT and Bz-MMT exhibited higher thermal stability than composites based on CTAB-MMT due to the well-dispersed nanoplatelets.

High resolution polarimeter-interferometer system for fast equilibrium dynamics and MHD instability studies on Joint-TEXT tokamak (invited)

A high-performance Faraday-effect polarimeter-interferometer system has been developed for the J-TEXT tokamak. This system has time response up to 1 μs, phase resolution < 0.1° and minimum spatial resolution ∼15 mm. High resolution permits investigation of fast equilibrium dynamics as well as magnetic and density perturbations associated with intrinsic Magneto-Hydro-Dynamic (MHD) instabilities and external coil-induced Resonant Magnetic Perturbations (RMP). The 3-wave technique, in which the line-integrated Faraday angle and electron density are measured simultaneously by three laser beams with specific polarizations and frequency offsets, is used. In order to achieve optimum resolution, three frequency-stabilized HCOOH lasers (694 GHz, >35 mW per cavity) and sensitive Planar Schottky Diode mixers are used, providing stable intermediate-frequency signals (0.5-3 MHz) with S/N > 50. The collinear R- and L-wave probe beams, which propagate through the plasma poloidal cross section (a = 0.25-0.27 m) vertically, are expanded using parabolic mirrors to cover the entire plasma column. Sources of systematic errors, e.g., stemming from mechanical vibration, beam non-collinearity, and beam polarization distortion are individually examined and minimized to ensure measurement accuracy. Simultaneous density and Faraday measurements have been successfully achieved for 14 chords. Based on measurements, temporal evolution of safety factor profile, current density profile, and electron density profile are resolved. Core magnetic and density perturbations associated with MHD tearing instabilities are clearly detected. Effects of non-axisymmetric 3D RMP in ohmically heated plasmas are directly observed by polarimetry for the first time.

Equilibrium reconstruction based on core magnetic measurement and its applications on equilibrium transition in Joint-TEXT tokamak

Evaluation and reconstruction of plasma equilibrium, especially to resolve the safety factor profile, is imperative for advanced tokamak operation and physics study. Based on core magnetic measurement by the high resolution laser polarimeter-interferometer system (POLARIS), the equilibrium of Joint-TEXT (J-TEXT) plasma is reconstructed and profiles of safety factor, current density, and electron density are, therefore, obtained with high accuracy and temporal resolution. The equilibrium reconstruction procedure determines the equilibrium flux surfaces essentially from the data of POLARIS. Refraction of laser probe beam, a major error source of the reconstruction, has been considered and corrected, which leads to improvement of accuracy more than 10%. The error of reconstruction has been systematically assessed with consideration of realistic diagnostic performance and scrape-off layer region of plasma, and its accuracy has been verified. Fast equilibrium transitions both within a single sawtooth cycle and during the penetration of resonant magnetic perturbation have been investigated.

Targeting MgrA-mediated virulence regulation in Staphylococcus aureus

Increasing antibiotic resistance in human pathogens necessitates the development of new approaches against infections. Targeting virulence regulation at the transcriptional level represents a promising strategy yet to be explored. A global transcriptional regulator, MgrA in Staphylococcus aureus, was identified previously as a key virulence determinant. We have performed a fluorescence anisotropy (FA)-based high-throughput screen that identified 5, 5-methylenedisalicylic acid (MDSA), which blocks the DNA binding of MgrA. MDSA represses the expression of α-toxin that is up-regulated by MgrA and activates the transcription of protein A, a gene down-regulated by MgrA. MDSA alters bacterial antibiotic susceptibilities via an MgrA-dependent pathway. A mouse model of infection indicated that MDSA could attenuate S. aureus virulence. This work is a rare demonstration of utilizing small molecules to block protein-DNA interaction, thus tuning important biological regulation at the transcriptional level.

Iron-catalysed oxidation intermediates captured in a DNA repair dioxygenase

Mononuclear iron-containing oxygenases conduct a diverse variety of oxidation functions in biology1,2, including the oxidative demethylation of methylated nucleic acids and histones3,4. E. coli AlkB is the first such enzyme that was discovered to repair methylated nucleic acids (Fig. 1)5,6, which are otherwise cytotoxic and/or mutagenic. AlkB human homologues are known to play pivotal roles in various processes7–11. Presented here is the first structural characterization of oxidation intermediates for these demethylases. Employing a chemical cross-linking strategy12,13, complexes of AlkB-dsDNA containing 1,N⁶-etheno adenine (εA), N³-methyl thymine (3-meT), and N³-methyl cytosine (3-meC) were stabilized and crystallized, respectively. Exposing these crystals, grown under anaerobic conditions containing iron(II) and α-ketoglutarate (αKG), to dioxygen initiates oxidation in crystallo (Supplementary Fig. 1). A glycol (from εA) and a hemiaminal (from 3-meT) intermediates are captured; a zwitterionic intermediate (from 3-2 meC) is also proposed, based on crystallographic observations and computational analysis. The observation of these unprecedented intermediates provides direct support for the oxidative demethylation mechanism for these demethylases. This study also depicts a general mechanistic view of how a methyl group is oxidatively removed from different biological substrates.

Structure determination of DNA methylation lesions N1-meA and N3-meC in duplex DNA using a cross-linked protein-DNA system

N(1)-meA and N(3)-meC are cytotoxic DNA base methylation lesions that can accumulate in the genomes of various organisms in the presence of S(N)2 type methylating agents. We report here the structural characterization of these base lesions in duplex DNA using a cross-linked protein-DNA crystallization system. The crystal structure of N(1)-meA:T pair shows an unambiguous Hoogsteen base pair with a syn conformation adopted by N(1)-meA, which exhibits significant changes in the opening, roll and twist angles as compared to the normal A:T base pair. Unlike N(1)-meA, N(3)-meC does not establish any interaction with the opposite G, but remains partially intrahelical. Also, structurally characterized is the N(6)-meA base modification that forms a normal base pair with the opposite T in duplex DNA. Structural characterization of these base methylation modifications provides molecular level information on how they affect the overall structure of duplex DNA. In addition, the base pairs containing N(1)-meA or N(3)-meC do not share any specific characteristic properties except that both lesions create thermodynamically unstable regions in a duplex DNA, a property that may be explored by the repair proteins to locate these lesions.

Highly sensitive and selective gold(I) recognition by a metalloregulator in Ralstonia metallidurans

A MerR family metalloregulatory protein CupR selectively responds to gold stress in Ralstonia metallidurans. A distorted trigonal geometry appears to be used by CupR to achieve the highly sensitive (K(d) approximately 10(-35) M) and selective recognition of gold(I).

Using the bias from flow to elucidate single DNA repair protein sliding and interactions with DNA

We perform single-molecule spatial tracking measurements of a DNA repair protein, the C-terminal domain of Ada (C-Ada) from Escherichia coli, moving on DNA extended by flow. The trajectories of single proteins labeled with a fluorophore are constructed. We analyze single-protein dwell times on DNA for different flow rates and conclude that sliding (with essentially no hopping) is the mechanism of C-Ada motion along stretched DNA. We also analyze the trajectory results with a drift-diffusion Langevin equation approach to elucidate the influence of flow on the protein motion; systematic variation of the flow enables one to estimate the microscopic friction. We integrate the step-size probability distribution to obtain a version of the fluctuation theorem that articulates the relation between the entropy production and consumption under the adjustable drag (i.e., bias) from the flow. This expression allows validation of the Langevin equation description of the motion. Comparison of the rate of sliding with recent computer simulations of DNA repair suggests that C-Ada could conduct its repair function while moving at near the one-dimensional diffusion limit.

Raman scattering spectroscopic study of n-tetradecane under high pressure and ambient temperature

The Raman spectroscopy of n-tetradecane was investigated in a Moissanite anvil cell at pressure from 0.1 MPa to 1.4 GPa and ambient temperature. The result shows that the liquid-solid phase transition of n-tetradecane takes place at around 302.8 MPa and the corresponding DeltaV(m) obtained is about -9.6 cm(-3)/mol. Above 302.8 MPa, the frequencies of CH(2) and CH(3) symmetric stretching and asymmetric stretching vibration shift to higher wave numbers in a linear manner with increasing pressure, which can be expressed as: nu(s)(CH(3))=0.013P+2882.0; nu(as)(CH(3))=0.014P+2961.6; nu(s)(CH(2))=0.013P+2850.8; nu(as)(CH(2))=0.009P+2923.2. This relationship indicates that n-tetradecane can be a reliable pressure gauge for the experimental study within the pressure range of 0.3-1.4 GPa.

A diazirine-based nucleoside analogue for efficient DNA interstrand photocross-linking

A diazirine-based nucleoside analogue (DBN) efficiently forms DNA interstand cross-linking under near-UV irradiation. This new base analogue may find broad applications in biotechnology and phototherapy.

Oxidative demethylation of 3-methylthymine and 3-methyluracil in single-stranded DNA and RNA by mouse and human FTO

The human obesity susceptibility gene, FTO, encodes a protein that is homologous to the DNA repair AlkB protein. The AlkB family proteins utilize iron(II), alpha-ketoglutarate (alpha-KG) and dioxygen to perform oxidative repair of alkylated nucleobases in DNA and RNA. We demonstrate here the oxidative demethylation of 3-methylthymine (3-meT) in single-stranded DNA (ssDNA) and 3-methyluracil (3-meU) in single-stranded RNA (ssRNA) by recombinant human FTO protein in vitro. Both human and mouse FTO proteins preferentially repair 3-meT in ssDNA over other base lesions tested. They showed negligible activities against 3-meT in double-stranded DNA (dsDNA). In addition, these two proteins can catalyze the demethylation of 3-meU in ssRNA with a slightly higher efficiency over that of 3-meT in ssDNA, suggesting that methylated RNAs are the preferred substrates for FTO.

Multiple logistic regression analysis of risk factors for carcinogenesis of oral submucous fibrosis in mainland China

Oral submucous fibrosis (OSF), a chronic progressive disorder, is regarded as the premalignant lesion of oral squamous cell carcinoma (OSCC). Its distribution is associated with chewing betel quid (BQ). The objective of the present study was to investigate risk factors for the carcinogenesis of OSF in mainland China. A case-control study was performed in 42 patients with OSCC that originated from OSF and 40 OSF controls. Epidemiological data and information related to risk factors were collected using a short structured questionnaire. Odd ratios (OR) and 95% confidence intervals (CI) were derived from logistic regression analysis. In multivariate analysis, only age, duration of BQ chewing, duration of cigarette smoking, and OSF accompanied by oral leukoplakia or oral lichen planus were associated with significantly increased risk for the malignant transformation of OSF. These findings contribute to current knowledge on the prevention of carcinogenesis of OSF in mainland China.

Crystal structures of DNA/RNA repair enzymes AlkB and ABH2 bound to dsDNA

Escherichia coli AlkB and its human homologues ABH2 and ABH3 repair DNA/RNA base lesions by using a direct oxidative dealkylation mechanism. ABH2 has the primary role of guarding mammalian genomes against 1-meA damage by repairing this lesion in double-stranded DNA (dsDNA), whereas AlkB and ABH3 preferentially repair single-stranded DNA (ssDNA) lesions and can repair damaged bases in RNA. Here we show the first crystal structures of AlkB-dsDNA and ABH2-dsDNA complexes, stabilized by a chemical cross-linking strategy. This study reveals that AlkB uses an unprecedented base-flipping mechanism to access the damaged base: it squeezes together the two bases flanking the flipped-out one to maintain the base stack, explaining the preference of AlkB for repairing ssDNA lesions over dsDNA ones. In addition, the first crystal structure of ABH2, presented here, provides a structural basis for designing inhibitors of this human DNA repair protein.

FDTD Simulation of Nonlinear Ultrasonic Pulse Propagation in ESWL

The extracorporeal shock wave lithotripsy (ESWL) has come into wide use due to its non-invasive advantage. However, as for the shock wave propagation in human body in relation to practical lithotripsy, there are a few studies on numerical simulation based on models conforming to practical situations. In this paper we report a numerical method of finite difference time domain (FDTD) for analyzing ultrasonic pulse nonlinear propagation in human body tissues and demonstrated it through an experiment of Reichenberger's ESWL in water.

Pulsed Rayleigh wave scattered at a surface crack

This paper investigates Rayleigh wave interaction with machined slots on flat aluminium blocks to simulate surface breaking cracks. Using a finite element method, Rayleigh wave scattering by narrow slots of varied depth ranging from 0.5 mm to 20 mm is calculated. Pulsed wideband Rayleigh waves with a centre frequency of 590 kHz and -6 dB bandwidth of 520 kHz is considered. Reflection and transmission coefficients are calculated and compare well with the published literature. We and other workers have reported enhancement of the measured amplitude or particle velocity of an apparent Rayleigh wave close to a surface defect. In this paper, it is found that the predicted enhancement of in-plane components of particle velocities close to a crack is significantly higher than that of the out-of-plane components of particle velocities which appears to be mainly due to the mode-converted surface skimming longitudinal wave from the crack that has mainly in-plane components near the sample surface. The enhancement of the in-plane particle velocity will be observed regardless of the type of in-plane sensitive ultrasonic detector used. The explanation of the discrepancy of the reflection and transmission coefficients obtained by pulsed and narrow band or pseudo continuous Rayleigh waves is discussed. The later-arriving Rayleigh waves from reverberation along the inside of the crack surface are observed, as has been previously reported by other workers, and this may also be used to gauge slot depth.

Depth gauging of defects using low frequency wideband Rayleigh waves

In non-destructive testing for cracks it is not sufficient to simply detect the presence of a defect, but it is essential to have an accurate measure of the depth. Accurate calibration of the techniques used to gauge defect size is therefore necessary. Recent progress in the field of non-contact ultrasonic testing has led to the development of a practically viable system for generating and detecting wideband Rayleigh waves on electrically conducting or magnetic samples using electro-magnetic acoustic transducers (EMATs). This system has been used to gauge the depth and position of surface breaking defects, and has many applications including metal billet testing and detecting and sizing gauge corner cracking in rails. In this paper we report experiments calibrating the response of EMATs when a defect is present between the generator and receiver, using a calibration sample with slots machined perpendicular to the surface to simulate surface breaking cracks. The depth of the defect can be gauged in the time domain and frequency domain, with an accurate 'fingerprint' of the position given by an enhancement of the signal when the receiver is close to the defect. The best choice of EMAT design for different applications is discussed, as is the best position for the receive EMAT to avoid areas of interference between the Rayleigh wave and bulk waves diffracted from the crack tip.

Gbetagamma affinity for bovine rhodopsin is determined by the carboxyl-terminal sequences of the gamma subunit

Two native betagamma dimers, beta(1)gamma(1) and beta(1)gamma(2), display very different affinities for receptors. Since these gamma subunits differ in both primary structure and isoprenoid modification, we examined the relative contributions of each to Gbetagamma interaction with receptors. We constructed baculoviruses encoding gamma(1) and gamma(2) subunits with altered CAAX (where A is an aliphatic amino acid) motifs to direct alternate or no prenylation of the gamma chains and a set of gamma(1) and gamma(2) chimeras with the gamma(2) CAAX motif at the carboxyl terminus. All the gamma constructs coexpressed with beta(1) in Sf9 cells yielded beta(1)gamma dimers, which were purified to near homogeneity, and their affinities for receptors and Galpha were quantitatively determined. Whereas alteration of the isoprenoid of gamma(1) from farnesyl to geranylgeranyl and of gamma(2) from geranylgeranyl to farnesyl had no impact on the affinities of beta(1)gamma dimers for Galpha(t), the non-prenylated beta(1)gamma(2) dimer had significantly diminished affinity. Altered prenylation resulted in a <2-fold decrease in affinity of the beta(1)gamma(2) dimer for rhodopsin and a <3-fold change for the beta(1)gamma(1) dimer. In each case with identical isoprenylation, the beta(1)gamma(2) dimer displayed significantly greater affinity for rhodopsin compared with the beta(1)gamma(1) dimer. Furthermore, dimers containing chimeric Ggamma chains with identical geranylgeranyl modification displayed rhodopsin affinities largely determined by the carboxyl-terminal one-third of the protein. These results indicate that isoprenoid modification of the Ggamma subunit is essential for binding to both Galpha and receptors. The isoprenoid type influences the binding affinity for receptors, but not for Galpha. Finally, the primary structure of the Ggamma subunit provides a major contribution to receptor binding of Gbetagamma, with the carboxyl-terminal sequence conferring receptor selectivity.

Independent and synergistic interaction of retinal G-protein subunits with bovine rhodopsin measured by surface plasmon resonance

We have used surface plasmon resonance (SPR) measurements for the kinetic analysis of G-protein-receptor interaction monitored in real time. Functionally active rhodopsin was immobilized on an SPR surface, with full retention of biochemical specific activity for catalysis of nucleotide exchange on the retinal G-protein alpha subunit, via binding to immobilized concanavalin A. The binding interactions of bovine retinal alpha(t) and beta(1)gamma(1) subunits with rhodopsin measured by SPR were profoundly synergistic. Synergistic binding of the retinal G-protein subunits to rhodopsin was not observed for guanosine 5'-[gamma-thio]triphosphate-bound Galpha(t), nor was binding observed with squid retinal Galpha(q), which is not activated by bovine rhodopsin. The binding affinity (336+/-171 nM; mean value+/-S.D.) of retinal betagamma for rhodopsin in the presence of retinal alpha subunit measured by SPR confirmed the apparent affinity of 254 nM determined previously by nucleotide exchange assays. Binding of beta(1)gamma(1), beta(1)gamma(2), and beta(1)gamma(8-olf) dimers to rhodopsin, independently of the alpha subunit, was readily observable by SPR. Further, these dimers, differing only in their gamma subunit compositions, displayed markedly distinct binding affinities and kinetics. The beta(1)gamma(2) dimer bound with a kinetically determined K(d) of 13+/-3 nM, a value nearly identical with the biochemically determined K(1/2) of 10 nM. The physiologically appropriate beta(1)gamma(1) displayed rapid association and dissociation kinetics, whereas the other beta(1)gamma dimers dissociated at a rate less than 1/100 as fast. Thus rhodopsin interaction with its native signalling partners is both rapid and transient, whereas the interaction of rhodopsin with heterologous Gbetagamma dimers is markedly prolonged. These results suggest that the duration of a G-protein-coupled receptor signalling event is an intrinsic property of the G-protein coupling partners; in particular, the betagamma dimer.

Two amino acids in the sixth transmembrane segment of the mouse gastrin-releasing peptide receptor are important for receptor activation

The gastrin-releasing peptide receptor (GRP-R) is a G protein-coupled receptor that mediates a variety of cellular responses, including cell growth and modulation of neuronal activity by activation of heterotrimeric GTP-binding proteins in the Gq family. To understand the regulation of GRP-R signaling we have substituted alanine for each of 10 amino acid residues within the transmembrane (TM) helices of the GRP-R predicted to project into the binding pocket of the receptor and analyzed the importance of each of these residues for receptor function. Two mutations showed selective loss of either agonist (Y285A) or antagonist (F313A) affinity for the GRP-R. In addition, we identified two amino acid residues, Phe(270) and Asn(281), in the sixth TM segment, which are important for receptor-G protein interaction. In a competition-binding assay with an antagonist radioligand, bombesin showed a 20- to 100-fold decreased affinity for the N281A and F270A mutant GRP-R compared with wild-type GRP-R. The saturation-binding isotherms are best fit by a two-state model, indicating that the receptors are in either a low-affinity (K(D2)) or a high-affinity (K(D1)) state. The ratio of the two affinities (K(D2)/K(D1)) was significantly increased for both mutants compared with wild-type GRP-R, whereas the fraction of mutant receptors in the high-affinity state (R(1)) was decreased. GDP/guanosine-5'-O-(3-thio)triphosphate exchange catalyzed by the N281A mutant was lower than that observed for the wild-type GRP-R. However, for both mutants, bombesin was still able to stimulate 1,4,5-inositol triphosphate in transfected cells albeit with reduced activity. We conclude that these two TM residues are important for receptor-G protein coupling, and postulate that each mutation may affect GRP-R conformational change to the high-affinity, G protein-coupled state.