Biomedical subjects

Xiaogang Wang

Publications and source records attributed to Xiaogang Wang.

7 recordsLinked to original sources

PubMed2006

The armadillo repeats of the Ufd4 ubiquitin ligase recognize ubiquitin-fusion proteins.

Armadillo (ARM) repeats have been identified in proteins regulating cell junction assembly, nuclear transport and transcription activation. Recent studies showed that a large number of ubiquitin (Ub) ligases (or E3s) also contain ARM repeats. The function of the ARM repeats in these E3s, however, remains unknown. Here we report that the ARM repeats of Ufd4, the E3 component of the UFD (Ub fusion degradation) pathway, recognize the Ub degradation signal of the UFD substrates. Disruption of the ARM repeats abolishes the ubiquitylating activity of Ufd4. This study uncovers a new role of the ARM repeats in protein ubiquitylation.

Amino Acid Sequence↗

PubMed2006

A nested molecule-independent neural network approach for high-quality potential fits.

It is shown that neural networks (NNs) are efficient and effective tools for fitting potential energy surfaces. For H2O, a simple NN approach works very well. To fit surfaces for HOOH and H2CO, we develop a nested neural network technique in which we first fit an approximate NN potential and then use another NN to fit the difference of the true potential and the approximate potential. The root-mean-square error (RMSE) of the H2O surface is 1 cm(-1). For the 6-D HOOH and H2CO surfaces, the nested approach does almost as well attaining a RMSE of 2 cm(-1). The quality of the NN surfaces is verified by calculating vibrational spectra. For all three molecules, most of the low-lying levels are within 1 cm(-1) of the exact results. On the basis of these results, we propose that the nested NN approach be considered a method of choice for both simple potentials, for which it is relatively easy to guess a good fitting function, and complicated (e.g., double well) potentials for which it is much harder to deduce an appropriate fitting function. The number of fitting parameters is only moderately larger for the 6-D than for the 3-D potentials, and for all three molecules, decreasing the desired RMSE increases only slightly the number of required fitting parameters (nodes). NN methods, and in particular the nested approach we propose, should be good universal potential fitting tools.

Journal Article↗

PubMed2006

[Pathological changes in neuromuscular junction during ischemia-reperfusion in rat skeletal muscle].

OBJECTIVE: To investigate the pathological changes in the neuromuscular junction during ischemia-reperfusion (IR) in the skeletal muscle. METHODS: Forty-eight healthy adult Wistar rats (24 male, 24 female) were equally randomised into the following 6 groups: Group A (control group): no ischemia-reperfusion; Group B: ischemia by clamping the blood vessels of the right hindlimb for 3 hours; Group C: ischemia by clamping for 4.5 hours; Group D: ischemia by the clamping for 4.5 hours followed by reperfusion for 1.5 hours; Group E: ischemia for 4.5 hours followed by reperfusion for 24 hours; and Group F: ischemia for 4. 5 hours followed by reperfusion for 2 weeks. Then, the medial head of the gastrocnemius muscle flap model was applied to the right hindlimb of each rat. The medial head of the gastrocnemius muscle was isolated completely,leaving only the major vascular pedicle, nerve and tendons intact. The proximal and distal ends (tendons) were ligated while the vessel pedicle was clamped. And then, Parameters of the muscle (performance, contraction index, colour, edema, bleeding) were observed. The muscle harvested was stained with gold chloride (AuCl3) and the enzyme histochemistry assay (succinate dehydrogenase combined with acetylcholine esterase) was performed. Morphology and configuration of the neuromuscular junction were observed during the ischemia-reperfusion injury by means of the AuCl3 staining. The result of the enzymehistochemical reactions was quantitatively analyzed with the computer image-analysis system. And then, additional 5 rats were prepared for 3 different models identical with those in Groups A, C and E separately. The specimens were harvested from each rat and were stained with HE and AuCl3, and they were examined under the light microscope. RESULTS: During the period of ischemia, the skeletal muscle of Group B showed the colour of purple and edema. The colour and edema became worse in Group C,while dysfunction of elasticity and contraction appeared obviously with plenty of dark red hemorrhagic effusion at the same time. After reperfusion,the color and edema of muscle in Group D became improved while the elasticity and function of contraction was not improved. Hemorrhagic effusion of Group D turned clearer and less than Group C. Group E was similar to Group D in these aspects of muscle except for much less hemorrhagic effusion. Skeletal muscle in Group F showed colour of red alternating with white, adhesion, contracture of muscle, exposure of necrotic yellow tissue and almost lost all its functions. The AuCl3 staining showed that during IR, necrosis of the myocytes was followed by degeneration of their neuromuscular junctions, and finally the nerve fibers attached to these neuromuscular junctions were disrupted like the withering of leaves. The enzyme histochemistry assay showed that there was no significant difference in the level of acetylcholine esterase between the ischemic group (Groups B and C) and the control group (Group A) (P>0.05). However, the level of acetylcholine esterase in all the reperfused groups (Groups D, E and F) decreased significantly when compared with the control group (Group A) and the ischemic groups (Groups B and C) (P<0.01). CONCLUSION: The distribution of the nerve fibers and the neuromuscular junctions in the mass of the muscles is almost like the shape of a tree. The neuromuscular junction seems to be more tolerant for ischemia than the myocyte. Survival of the neuromuscular junction depends on its myocytes alive. Therefore, an ischemia-reperfusion injury will not be controlled unless an extensive debridement of the necrotic muscle is performed.

Animals↗

PubMed2005

Effect of microbial fermentation on caffeine content of tea leaves.

Caffeine is widely used in the food and pharmaceutical industries. For safety concerns, natural caffeine is preferred over synthetic products despite of its high cost. To explore more economical methods of acquiring natural caffeine, we adopted a microbial fermentation technique to increase the caffeine content of tea leaves. Our studies showed that the caffeine content in tea leaves increased reasonably after treating leaves with microorganisms for a period of time (i.e. orthodox pile-fermentation), and the amount of caffeine content increase varied significantly between black and green teas (27.57% and 86.41%). These results suggested that the change of caffeine content in tea leaves during the pile-fermentation depended not only on the growth and reproduction of microorganisms, but also on the tea composition.

Caffeine↗

PubMed2004

A unified framework for subspace face recognition.

PCA, LDA, and Bayesian analysis are the three most representative subspace face recognition approaches. In this paper, we show that they can be unified under the same framework. We first model face difference with three components: intrinsic difference, transformation difference, and noise. A unified framework is then constructed by using this face difference model and a detailed subspace analysis on the three components. We explain the inherent relationship among different subspace methods and their unique contributions to the extraction of discriminating information from the face difference. Based on the framework, a unified subspace analysis method is developed using PCA, Bayes, and LDA as three steps. A 3D parameter space is constructed using the three subspace dimensions as axes. Searching through this parameter space, we achieve better recognition performance than standard subspace methods.

Algorithms↗

PubMed2003

Wave dispersion relations in two-dimensional Yukawa systems.

Collective modes in a two-dimensional Yukawa system are investigated by molecular dynamics simulation in a wide range of coupling parameter Gamma and screening strength kappa. The dispersion relations and sound speeds of the transverse and longitudinal waves obtained for hexagonal lattice are in agreement with the theoretical results. The negative dispersion of the longitudinal wave is demonstrated. Frequency gaps are found on the dispersion curves of the transverse wave due to scattering of the waves on lattice defects for proper values of Gamma. The common frequency of transverse and longitudinal waves drops dramatically with the increasing screening strength kappa.

Journal Article↗

PubMed2002

Self-consistent nonlinear resonance and hysteresis of a charged microparticle in a RF sheath.

A self-consistent model is proposed to study nonlinear phenomena, such as secondary resonance and hysteresis in the vertical oscillations of a charged microparticle in a radio-frequency sheath. The motion of a single microparticle in the sheath is simulated by solving Newton's equation in which various forces acting on the particle are taken into account. The particle charging and the sheath electric field are described by a self-consistent model of the collisional radio-frequency sheath dynamics. It is found that the nonlinearity is related to the particle's charge, the sheath electric field, and the external excitation force, as well as the ion drag force and neutral-gas friction on the particle.

Journal Article↗