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5,10-Methylenetetraydrofolate reductase (MTHFR) is a key enzyme in folate metabolism. MSMEG_6649, a non-canonical MTHFR from Mycobacterium smegmatis, was previously reported as a monomeric protein lacking the flavin coenzyme. However, the structural basis for its unique flavin-independent catalytic mechanism remains poorly understood. Here, we determined the crystal structures of apo MTHFR MSMEG_6649 and its complex with NADH from M. smegmatis. Structural analysis revealed that the groove formed by the loops 4 and 5 of non-canonical MSMEG_6649 interacting with FAD was significantly larger than that of canonical MTHFR. Meanwhile, the NADH-binding site in MSMEG_6649 is highly similar to the FAD binding site in canonical MTHFR, suggesting that NADH plays the same role (immediate hydride donor for methylenetetraydrofolate) as FAD in the catalytic reaction. Using biochemical analysis, molecular modeling, and sitedirected mutagenesis, the critical residues participating in the binding of NADH and the substrate 5,10-methylenetetrahydrofolate as well as the product 5-methyltetrahydrofolate were identified and validated. Taken together, this work not only provides a good starting point for understanding the potential catalytic mechanism for MSMEG_6649, but also identifies an exploitable target for the development of anti-mycobacterial drugs. [ABSTRACT FROM AUTHOR]

Background: China is a multi-ethnic country. It is of great significance for the skull identification to realize the skull ethnic classification through computers, which can promote the development of forensic anthropology and accelerate the exploration of national development. Methods: In this paper, the 3D skull model is transformed into 2D auxiliary image including curvature, depth and elevation information, and then the deep learning method of the 2D auxiliary image is used for ethnic classification. We construct a convolution neural network structure inspired by VGGNet16 which has achieved excellent performance on image classification. In order to optimize the network, Adam algorithm is adopted to avoid falling into local minimum, and to ensure the stability of the algorithm with regularization terms. Results: Experiments on 400 skull models have been conducted for ethnic classification by our method. We set different learning rates to compare the performance of the model, the highest accuracy of ethnic classification is 98.75%, which have better performance than other five classical neural network structures. Conclusions: Deep learning based on skull auxiliary image for skull ethnic classification is an automatic and effective method with great application significance. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) transverse vibration was reported based on the molecular structural mechanics model for microtubules (MTs), where the bending axis of the cross section rotates in an anticlockwise direction and the adjacent half-waves oscillate in different planes. Herein, efforts were invested to capturing the physics behind the observed phenomenon and identifying the important factors that influence the rotation angle between two adjacent half waves. A close correlation was confirmed between the rotation of the oscillation planes and the helical structures of the MTs, showing that the 3D mode is a result of the helicity found in the MTs. Subsequently, the wave length-dependence and the boundary condition effects were also investigated for the 3D transverse vibration of the MTs. In addition, the vibration frequency was found to remain the same in the presence or absence of the bending axis rotation. This infers that the unique vibration mode is merely due to the bending axis rotation of the cross section, but no significant torsion occurs for the MTs. [ABSTRACT FROM AUTHOR]

The size scale effect on the pyroelectric properties is studied for gallium nitride (GaN) nanowires (NWs) based on molecular dynamics simulations and the theoretical analysis. Due to the significant influence of the surface thermoelasticity and piezoelectricity at the nanoscale, the pyroelectric coefficient of GaN NWs is found to depend on the cross-sectional size. This size-dependent pyroelectric coefficient of GaN NWs together with the size-dependent dielectric constant reported in our previous study is employed to study the pyroelectric potential of GaN NWs subjected to heating. The results show that the size scale effect is significant for thin NWs (cross-sectional size in nanometers) and may raise the pyroelectric potential of GaN NWs by over 10 times. Such a size scale effect on the pyroelectric properties of NWs originates from the influence of thermoelasticity, piezoelectricity, and dielectricity at the nanoscale and decreases with increasing cross-section of GaN NWs. It is expected that the present study may have strong implication in the field of energy harvesting at the nanoscale, as pyroelectricity offers a new avenue to the design of novel nanogenerators. [ABSTRACT FROM AUTHOR]

A great deal of research attention has been devoted to studying the effects of customer concentration on firm strategic acts. Scholars have also investigated the relationship between customer concentration and firm innovation, but concluded inconsistent findings of such relationship. Furthermore, the underlying mechanism remains unclear. To address these concerns, this study decouples exploratory innovation from firm innovation and introduce performance-reducing threats perceived by the executives as the mediator. Based on the observations of China high-tech listed firms from 2011 to 2018, empirical results show that customer concentration has a U-shaped relationship with exploratory innovation, via the mediating effect of performance-reducing threats perceived by the executives. [ABSTRACT FROM AUTHOR]

We carried out a systematic investigation of packing structures of a series of dimethoxyanthracenes, i.e., 1,4- (1), 1,8- (2), 1,5- (3), 2,6- (4), and 2,7-derivatives (5). The packing structures of the dimethoxyanthracenes are classified into two types, a rubrene-like pitched π-stack (1–3) and a typical herringbone packing (4 and 5), which evidently show that the position of methoxy groups is crucial to determine the packing structure of dimethoxyanthracenes. Effects of the substitution position on intermolecular interactions are analyzed by the noncovalent intermolecular interaction (NCI) method, Hirshfeld surface analysis, and symmetry-adapted perturbation theory (SAPT) method, thus clarifying active roles of the methoxy groups in the formation of rubrene-like pitched π-stack. The present results shed light on a molecular design strategy to realize the rubrene-like pitched π-stack in the solid state, which had been regarded as a packing structure limited for rubrene and its closely related derivatives. [ABSTRACT FROM AUTHOR]

D-xylose, the main building block of plant biomass, is a pentose sugar that can be used by bacteria as a carbon source for bio-based fuel and chemical production through fermentation. In bacteria, the first step for D-xylose metabolism is signal perception at the membrane. We previously identified a three-component system in Firmicutes bacteria comprising a membrane-associated sensor protein (XylFII), a transmembrane histidine kinase (LytS) for periplasmic D-xylose sensing, and a cytoplasmic response regulator (YesN) that activates the transcription of the target ABC transporter xylFGH genes to promote the uptake of D-xylose. The molecular mechanism underlying signal perception and integration of these processes remains elusive, however. Here we purified the N-terminal periplasmic domain of LytS (LytSN) in a complex with XylFII and determined the conformational structures of the complex in its D-xylose--free and D-xylose--bound forms. LytSN contains a four-helix bundle, and XylFII contains two Rossmann fold-like globular domains with a xylose-binding cleft between them. In the absence of D-xylose, LytSN and XylFII formed a heterodimer. Specific binding of D-xylose to the cleft of XylFII induced a large conformational change that closed the cleft and brought the globular domains closer together. This conformational change led to the formation of an active XylFII-LytSN heterotetramer. Mutations at the D-xylose binding site and the heterotetramer interface diminished heterotetramer formation and impaired the D-xylose--sensing function of XylFII-LytS. Based on these data, we propose a working model of XylFII-LytS that provides a molecular basis for D-xylose utilization and metabolic modification in bacteria. [ABSTRACT FROM AUTHOR]

Furongian (upper Cambrian) conodonts from the Shenjiawan Formation, Wa'ergang section, Taoyuan County, Hunan Province, South China are described. The Wa'ergang section has been proposed as a potential GSSP for the base of the uppermost stage of the Cambrian System, at the first appearance of the agnostoid trilobite Lotagnostus americanus. The Shenjiawan Formation consists of limestone with intercalations of marlstone and shale. The conodont yielding is low and the preservation is moderate. The conodont fauna includes proto-, para- and euconodonts. Conodont taxa characteristic of North China, South China and Korea occur together with cosmopolitan taxa. The biostratigraphic distribution of conodonts is directly correlated with the agnostoid trilobite biozones, with the base of the Proconodontus posterocostatus Zone very close to the base of the Lotagnostus americanus trilobite Zone. [ABSTRACT FROM AUTHOR]

A hybrid nanowire (HNW) was constructed by coating a single-wall carbon nanotube (SWCNT) with piezoelectric zinc oxide (ZnO). The two components of the HNW interact with each other via the van derWaals (vdW) force. This paper aims to study the effect of the piezoelectricity in the ZnO layer and the inter-phase vdW interaction on the fundamental vibration of the HNWs. In doing this, a new model was developed where the two components of the HNWs were modeled as Euler beams coupled via the interphase vdW interaction. Based on the model, the dependence of the frequency on an applied electrical voltage was calculated for HNWs of different geometric sizes to reveal the voltage effect. The results were then compared with those calculated without considering the inter-phase vdW interaction. It was found that the interphase vdW interaction can substantially decrease the structural stiffness, leading to a greatly enhanced piezoelectric effect but a lower frequency for the vibration of the HNWs. [ABSTRACT FROM AUTHOR]

Rifampin (RIF) is a first-line drug used for the treatment of tuberculosis and other bacterial infections. Various RIF resistance mechanisms have been reported, and recently an RIF-inactivation enzyme, RIF phosphotransferase (RPH), was reported to phosphorylate RIF at its C21 hydroxyl at the cost of ATP. However, the underlying molecular mechanism remained unknown. Here, we solve the structures of RPH from Listeria monocytogenes (LmRPH) in different conformations. LmRPH comprises three domains: an ATP-binding domain (AD), an RIF-binding domain (RD), and a catalytic His-containing domain (HD). Structural analyses reveal that the C-terminal HD can swing between the AD and RD, like a toggle switch, to transfer phosphate. In addition to its catalytic role, the HD can bind to the AD and induce conformational changes that stabilize ATP binding, and the binding of the HD to the RD is required for the formation of the RIF-binding pocket. A line of hydrophobic residues forms the RIF-binding pocket and interacts with the 1-amino, 2-naphthol, 4-sulfonic acid and naphthol moieties of RIF. The R group of RIF points toward the outside of the pocket, explaining the low substrate selectivity of RPH. Four residues near the C21 hydroxyl of RIF, His825, Arg666, Lys670, and Gln337, were found to play essential roles in the phosphorylation of RIF; among these the His825 residue may function as the phosphate acceptor and donor. Our study reveals the molecular mechanism of RIF phosphorylation catalyzed by RPH and will guide the development of a new generation of rifamycins. [ABSTRACT FROM AUTHOR]

The article offers information on the advantages of nanostructured conjugated polymers for stable and fast lithium storage anodes. Topics discussed include its applications in portable consumer electronics and electric vehicles, development of new inorganic electrodes and construction of organic polymers with a stable skeleton.

Based on a molecular mechanics approach pre-buckling and buckling deformations are studied for boron nitride nanotubes (BNNTs) and nanosheets (BNNSs) subject to an electrical field. Due to the reverse piezoelectric effect a compressive or shear force is generated for those of zigzag and armchair structures, respectively. As a result, axial deformation and buckling occur for zigzag BNNTs and BNNSs, while a torsional or shear deformation occurs for their armchair counterparts, followed by the corresponding buckling. The critical buckling electrical field is also studied and found to decrease as the aspect ratio of BNNTs and BNNSs increases. Such an effect of the aspect ratio turns out to be more pronounced for the buckling of armchair BNNTs and BNNSs. [ABSTRACT FROM AUTHOR]

The value of combined application of both ECG-gated cine MRA and 3D-CEMRA in the detection of large intracranial aneurysms was evaluated and the findings were compared with those of conventional MRA and DSA. Twenty-four patients with 26 large intracranial aneurysms underwent MRI and DSA. All these aneurysms, diameter from 15 to 39 mm, were located at internal cerebral artery ( n=12), vertebral artery ( n=3), basilar artery ( n=4), anterior cerebral artery ( n=2), middle cerebral artery ( n=2), anterior communicate artery ( n=2) and posterior communicate artery ( n=1). Thirteen cases of hematoma or cavernoma were studied as control group. All patients were examined on GE 1. 5T MR system. ECG-gated cine MRA was performed with 2D multi-phase fast gradient-recalled echo sequence in a single section. All the images were analyzed with signal intensity VS time curve for differentiating intraaneurysmal blood flow from static tissue. The results were analzsed by statistic “ t” test. 3D-CEMRA was performed with spoiled gradient-recalled echo and one dose of Gd-DTPA. All data was processed with multi-plannar reformat (MPR) and tomography for the demonstration of aneurysms in detail. All 26 aneurysms were demonstrated successfully by combined application of both cine MRA and 3D-CEMRA. Compared to DSA and conventional 3D-MOTSA, its sensitivity and specificity figures were both 100%. Cine MRA could differentiate the blood flow from the static tissue. The intensity VS time curves of intraaneurysmal blood flow offered fluctuating form and average signal change between systole and diastole period was about 89.8±37.4; However, under the control group, intraaneurysmal thrombus or cerebral hemorrhage or cavernomas had no significant signal change and the curves offered steady form with the average signal change being about 8.2±6.3. There was statistically significant difference between the intraaneurysmal blood flow and static tissue ( P=0.025, <0.05). 3D-CEMRA was very useful in demonstrating the aneurysmal size, intraaneurysmal thrombus formation, neck and the detailed relationship of the aneurysm to the surrounding structures. It was concluded that the combined application of both cine MRA and 3D-CEMRA might be a valuable clinical tool for the detection of large intracranial aneurysms. [ABSTRACT FROM AUTHOR]

The utility of three-dimensional spoiled gradient recalled acquisition in steady state (3D-SPGR) imaging in the cerebral diseases was evaluated and 3D-SPGR after enhancement in depicting contrast enhancement of all lesions and 2D-SE T1WI comparatively analyzed. 117 patients were subjected to MRI by a GE 1. 5T MR system. After performance of axial T1WI and T2WI in all patients, MRA (3D-MOTSA) images were acquired in 6 cases (8 lesions) of aneurysms. After enhancement, 3D-SPGR images were obtained in all the remaining patients. Quality parameters (SNR, C and CNR) were calculated on enhanced 2D-SE T1WI and 3D-SPGR images. And a four-point scale was used to measure the signal intensity of the main lesions on both sequences, then statistical analysis of the average score was performed with “ t” test. Except for aneurysms, 2D-SE T1WI detected 134 lesions and 3D-SPGR disclosed 147 lesions. It was found that there was no statistically significant difference between the two average scores as determined by the “ t” test ( t=1.894, P>0.05). The enhancement degree of the main lesion was equivalent on 3D-SPGR and 2D-SE T1WI. Quality parameters (SNR, C and CNR) on 2D-SE T1WI were much larger than that of 3D-SPGR, increasing by an average of 57%, 20% and 97% respectively. 3D-SPGR imaging with MPR could clearly depict vascularity related to neoplasms in 20 cases and demonstrate shifted, deformed and blocked vessels involved by tumors. Six cases of large aneurysms (8 lesions) were visualized more clearly on 3D-SPGR than MRA (3D-MOTSA): 3D-SPGR could display aneurysm necks and differentiate thrombosed portion from the patent lumen, and disclose relationship of aneurysm to surrounding structures. It was concluded that enhanced 3D-SPGR played an important role in the depiction of the cerebral lesions and was superior to 2D-SE T1WI in many aspects. [ABSTRACT FROM AUTHOR]

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A novel scheme for the enhancement of phase sensitivity based on a Mach–Zehnder interferometer (MZI) and intensity detection is proposed. With the input of bright entangled twin beams from four wave mixing (FWM), the phase sensitivity can beat shot noise limit (SNL) and approach Heisenberg limit. This scheme is special due to that only one of bright entangled twin beams enters into the MZI and the other one is employed for measurement. In addition, by altering the parametric strength of FWM and the implementation of maximum quantum squeezing, the optimal phase sensitivity can reach sub-SNL. Optical intensity depletion of photon detectors and internal intensity depletion of the MZI are also discussed. The scheme displays that by employing external resources, while one input of the MZI is an vacuum beam, the phase sensitivity still can beat SNL. [ABSTRACT FROM AUTHOR]

In order to explore the MRI volume of the amygdala and hippocampus in patients with major depression, quantititive MRI of the amygdala and hippocampus were studied in 22 patients with major depression and compared with 13 age-matched controls. The results showed that both groups exhibited similar significant hippocampal asymmetry (left smaller than right). The volume of the bilateral hippocampus was significantly smaller in the major depression group than that in control group. The patients had significant asymmetry of the amygdalar volumes (right smaller than left). No correlation was found between hippocampal volume abnormalities and ill duration. It was concluded that the hippocampus and amygdala within limbic-cortical networks may play a crucial role in the pathogenesis of major depression. [ABSTRACT FROM AUTHOR]

The cricoarytenoid relationship presented with spiral computed tomography was demonstrated and the reconstruction of arytenoid dislocation was presented by using multiplanar reconstruction algorithms. Fifteen patients with arytenoid dislocation documented by fiberoptic laryngoscopy and strobovideolaryngoscopy and 10 normal persons were displayed by spiral computed tomography (CT). A making design of our own had been used to diagnose arytenoid dislocation on axial CT image. Results showed that dislocation of cricoarytenoid joint was consistently demonstrated on several of the overlapping thin axial reconstructions in each of the 15 patients, in whom asymmetry of the bilateral cricoarytenoid joints was noted on axial images. It was found that on the glottic-fissure level the basal angle on abnormal side was larger in 8 patients than that on the normal side and smaller in 7 patients in patient group, whereas right basal angle was equal to the left in 8 subjects, except 2 in control group. There was statistically significant difference in the number of the equal to two basal angles of glottic fissure between control group and patient group ( P<0.025). High-quality sagittal and coronal reconstructive images often were helpful in confirming or clarifying the complex arytenoid orientations. The findings that two-side basal angle was not equal in triangle of glottic fissure can be used as an objective parameter to diagnose arytenoid dislocation. Spiral CT is a useful adjunct in the diagnosis and treatment of dislocation of cricoarytenoid joint. [ABSTRACT FROM AUTHOR]

Hybrid boron nitride–carbon nanotubes (BN-CNTs) have attracted considerable attention in recent research. In this effort, molecular dynamics simulations were performed to study the fundamentals of BN-CNTs in tensile tests, i.e. Young’s modulus and fracture strength (strain). Particular attention was paid to the influence of the atomic structure, hybrid style, and BN concentration on the tensile properties. The morphological changes were also investigated for the BN-CNTs at the onset of fracture. It is noted that the Young’s modulus of BN-CNTs decreases almost linearly with increasing the BN concentration with a rate of change independent of the hybrid style. In contrast, the sensitivity of the fracture strength and fracture strain to the variation of BN concentration depends strongly on the hybrid style of BN-CNTs. These results are expected to significantly expand the knowledge of the elastic and fracture properties of novel nanostructures and facilitate their applications in bandgap-engineering. [ABSTRACT FROM AUTHOR]

A large scattering of effective atomic charge distribution was found in the literature for hexagonal boron nitride nanostructures (BNNSs). In our paper (Zhang J, Wang C Y and Sondipon A 2013 J. Phys. D: Appl. Phys. 46 235303) ‘±3e’ was chosen as a rough approximation for the effective atomic charge in BNNSs as it gave the piezoelectric coefficient of BNNSs close to the values in the literature. [ABSTRACT FROM AUTHOR]

Original article: EPL, 105 (2014) 28004. [ABSTRACT FROM AUTHOR]