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Biomedical subjects

B Zhang

Publications and source records attributed to B Zhang.

At least 289 records · Page 16Linked to original sources
PubMed1999

Functional domain analysis of the Saccharomyces MAL-activator.

MAL63 of the MAL6 locus and its homologues at the other MAL loci encode transcription activators required for the maltose-inducible expression of the MAL structural genes. We carried out a deletion analysis of LexA-MAL63 gene fusions to localize the functional domains of the Mal63 MAL-activator protein. Our results indicate that the sequence-specific DNA-binding domain of Mal63p is contained in residues 1-100; that residues 60-283 constitute a functional core region including the transactivation domain; that residues 251-299 are required to inhibit the activation function of Mal63p; and that the rest of the C-terminal region of the protein contains a maltose-responsive domain that acts to relieve the inhibitory effect on the activation function. Abundant overproduction of Mal63p does not overcome the negative regulation of MAL gene expression in the absence of maltose, suggesting that a titratable MAL-specific repressor similar to Gal80p is not involved in the negative regulation of the MAL-activator. A model for maltose-inducible autoregulation of the MAL-activator is presented.

Amino Acid Sequence↗
PubMed1999

Genetic variation at the matrix metalloproteinase-9 locus on chromosome 20q12.2-13.1.

Allelic association methods are better suited than linkage analysis for mapping of susceptibility genes that confer modest increases in risk in complex diseases. In both family- and population-based association studies, it is very useful to have prior knowledge of all sequence variants and the degree of linkage disequilibrium in a candidate gene region. In this study, we scanned sequence variants in a 2.2-kb promoter sequence and all 13 exons (totalling 3.3 kb) of the matrix metalloproteinase-9 gene, which is associated with coronary heart disease and a candidate for other diseases involving connective tissue remodelling, such as cancer metastasis. The sequences had a total of ten variable sites, four in the promoter, five in the coding region (three of which alter the amino acid encoded) and one in the 3' untranslated sequence. Sequence inspection suggests that some of the variants will have a functional impact on either level of expression or enzymatic activity. Tight linkage disequilibrium was detected between variants across the entire length of the gene (approximately 9 kb), and frequencies of different haplotypes were determined. The data provide an essential tool for studies of the possible contribution of genetic variation at the matrix metalloproteinase-9 locus to genetically determined susceptibility to a number of important diseases. The results also provide experimental data on the extent of linkage disequilibrium in the general population, which is yet to be resolved.

3' Untranslated Regions↗
PubMed1999

A kinetic molecular model of the reversible unfolding and refolding of titin under force extension.

Molecular elasticity is a physicomechanical property that is associated with a select number of polypeptides and proteins, such as the giant muscle protein, titin, and the extracellular matrix protein, tenascin. Both proteins have been the subject of atomic force microscopy (AFM), laser tweezer, and other in vitro methods for examining the effects of force extension on the globular (FNIII/Ig-like) domains that comprise each protein. In this report we present a time-dependent method for simulating AFM force extension and its effect on FNIII/Ig domain unfolding and refolding. This method treats the unfolding and refolding process as a standard three-state protein folding model (U right arrow over left arrow T right arrow over left arrow F, where U is the unfolded state, T is the transition or intermediate state, and F is the fully folded state), and integrates this approach within the wormlike chain (WLC) concept. We simulated the effect of AFM tip extension on a hypothetical titin molecule comprised of 30 globular domains (Ig or FNIII) and 25% Pro-Glu-Val-Lys (PEVK) content, and analyzed the unfolding and refolding processes as a function of AFM tip extension, extension rate, and variation in PEVK content. In general, we find that the use of a three-state protein-folding kinetic-based model and the implicit inclusion of PEVK domains can accurately reproduce the experimental force-extension curves observed for both titin and tenascin proteins. Furthermore, our simulation data indicate that PEVK domains exhibit extensibility behavior, assist in the unfolding and refolding of FNIII/Ig domains in the titin molecule, and act as a force "buffer" for the FNIII/Ig domains, particularly at low and moderate extension forces.

Amino Acid Sequence↗
PubMed1999

Quantity and function of high density lipoprotein as an indicator of coronary atherosclerosis.

OBJECTIVES: To examine the association between the fractional esterification rate of cholesterol (C) in low density lipoprotein- and very low density lipoprotein-depleted plasma (FER(HDL)) and coronary artery disease (CAD) and the influence of serum HDL-C levels. BACKGROUND: The function of HDL in reverse cholesterol transport is involved in the antiatherogenic action of HDL, and FER(HDL) is a newly established quantitative measure of HDL function in vivo. METHODS: Cases (n = 185, F/M: 43/142) and controls (n = 74, F/M:27/47) were defined as subjects with/without angiographically proven CAD, respectively. RESULTS: The cases had significantly (p < 0.05) higher FER(HDL) values (13.2+/-0.3 %/h vs. 12.1+/-0.5 %/h) and lower HDL-C levels (39.0+/-1.0 mg/dL vs. 46.8+/-1.4 mg/dL) than the controls. The associations of FER(HDL) and HDL-C with CAD were linear and significant (p < 0.05). Multiple logistic regression analysis indicated that the association of FER(HDL) with CAD varied with the HDL-C level: significant for the low HDL-C tertile (chi-square = 6.20, p < 0.05) but not significant for the middle and high HDL-C tertiles (chi-square = 0.08 and 0.03, n.s.). The risk of CAD, relative to that in patients with low FER(HDL) and high HDL-C, was higher in patients with low FER(HDL) and low HDL-C (odds ratio [95% confidence interval]: 2.37 [1.12-4.97], p < 0.05) and was highest in patients with high FER(HDL) and low HDL-C (3.85 [1.84-8.06], p < 0.01). CONCLUSIONS: The functional assay of HDL (FER(HDL)) is an independent risk factor for CAD. The combination of FER(HDL) and HDL-C could be a potent indicator for CAD, and may reflect a potential mechanism of atherosclerosis.

Biomarkers↗
PubMed1999

Angiotensin I converting enzyme gene polymorphism and insulin resistance in patients with angina pectoris.

The association between insertion/deletion polymorphism of the angiotensin I converting enzyme (ACE) gene and insulin resistance (IR) was investigated in 64 consecutive patients (F/M: 11/53) with angina pectoris without clinically manifest diabetes mellitus who underwent diagnostic coronary angiography. The observed frequency distribution of ACE genotypes did not deviate from that predicted from the Hardy-Weinberg equilibrium in this group. Patients with the ACE-ID genotype had significantly lower IR, as assessed by an oral glucose tolerance test (OGTT) and by homeostatic model assessment (HOMA), compared to those with the ACE-II genotype, as assessed by a multiple comparison analysis. Patients were divided into two groups with low and high HOMA-IR, and the I allele was seen more frequently in the high HOMA-IR group than in the low HOMA-IR group (0.62 v 0.47, respectively, by chi2 test, P < .05). Logistic regression analysis showed that the odds ratio for insulin resistance in patients with the II genotype, compared to those with the ID and DD-genotypes (assuming that the I allele has a recessive effect), was 4.0 (95% confidence interval, 1.2 to 16.5; P = .037), after adjusting for the presence of significant coronary atherosclerosis. In conclusion, the D allele was not associated with higher insulin resistance in patients with angina pectoris; that is, patients with the ID and DD genotypes were associated with a significantly lower risk of insulin resistance, compared to those with the II genotype.

Aged↗
PubMed1999

Age-dependent emergence and progression of a tauopathy in transgenic mice overexpressing the shortest human tau isoform.

Filamentous tau aggregates are hallmarks of tauopathies, e.g., frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17) and amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC). Since FTDP-17 tau gene mutations alter levels/functions of tau, we overexpressed the smallest human tau isoform in the CNS of transgenic (Tg) mice to model tauopathies. These mice acquired age-dependent CNS pathology similarto FTDP-17 and ALS/PDC, including insoluble, hyperphosphorylated tau and argyrophilic intraneuronal inclusions formed by tau-immunoreactive filaments. Inclusions were present in cortical and brainstem neurons but were most abundant in spinal cord neurons, where they were associated with axon degeneration, diminished microtubules (MTs), and reduced axonal transport in ventral roots, as well as spinal cord gliosis and motor weakness. These Tg mice recapitulate key features of tauopathies and provide models for elucidating mechanisms underlying diverse tauopathies, including Alzheimer's disease (AD).

Aging↗
PubMed1999

Regulation of vascular endothelial growth factor-dependent retinal neovascularization by insulin-like growth factor-1 receptor.

Although insulin-like growth factor 1 (IGF-1) has been associated with retinopathy, proof of a direct relationship has been lacking. Here we show that an IGF-1 receptor antagonist suppresses retinal neovascularization in vivo, and infer that interactions between IGF-1 and the IGF-1 receptor are necessary for induction of maximal neovascularization by vascular endothelial growth factor (VEGF). IGF-1 receptor regulation of VEGF action is mediated at least in part through control of VEGF activation of p44/42 mitogen-activated protein kinase, establishing a hierarchical relationship between IGF-1 and VEGF receptors. These findings establish an essential role for IGF-1 in angiogenesis and demonstrate a new target for control of retinopathy. They also explain why diabetic retinopathy initially increases with the onset of insulin treatment. IGF-1 levels, low in untreated diabetes, rise with insulin therapy, permitting VEGF-induced retinopathy.

Animals↗
PubMed1999

In vivo kinetics of human apolipoprotein A-I variants in rabbits.

BACKGROUND: Genetic variants of human apolipoprotein (apo) A-I, the major protein component of high-density lipoprotein (HDL), with a single amino acid substitution have been reported, and some of these result in very low plasma HDL-cholesterol (C) levels. Examining the kinetics of radiolabelled apolipoprotein is a straightforward technique for determining its metabolism in vivo. In this study, we investigated the in vivo kinetics of several human apo A-I variants, which we had identified previously, in rabbits. MATERIALS AND METHODS: Apo A-I variants from heterozygous carriers of Lys-107-->0, Lys-107-->Met, Pro-3-->Arg, Pro-4-->Arg, Pro-165-->Arg and Glu-198-->Lys and the corresponding normal apo A-I were purified and then radioiodinated with 131I and 125I. A kinetic study of apo A-I variants was performed in normolipidaemic rabbits after simultaneous injection of the two isotopes that had been incorporated into HDL. The fractional catabolic rate (FCR) was calculated from the radioactive decay curve. RESULTS: Acidic mature (negatively charged) apo A-I variants caused by a single amino acid substitution (Lys-107-->0, and Lys-107-->Met) were catabolized faster (FCR, 1.931 +/- 0.539 per day vs. 1.636 +/- 0.460 per day, P </= 0.01 using the Wilcoxon signed-rank test) and basic mature (positively charged) apo A-I variants (Pro-3-->Arg, Pro-4-->Arg, Pro-165-->Arg and Glu-198-->Lys) were catabolized more slowly (FCR 1.470 +/- 0.380 per day vs. 1.654 +/- 0.430 per day, P </= 0.01) than the corresponding normal mature apo A-I in vivo in rabbits. In addition, an inverse linear relationship was observed between the deviation in the FCR of variant human apo A-I from that of normal human apo A-I and the number of electric charges that the apo A-I variant carried (r = -0. 90, k = -0.188, P = 0.0003), as assessed by a linear regression analysis, suggesting that the electric charge of apo A-I variants may determine, at least in part, its in vivo kinetics in rabbits. CONCLUSIONS: Genetic variants of apo A-I with a single amino acid substitution show abnormal kinetics, and the electric charge of a apo A-I variant could contribute to determining its kinetics in vivo in this xenologous model.

Animals↗
PubMed1999

Muscle cells become necrotic rather than apoptotic during reperfusion of ischaemic skeletal muscle.

While necrosis is known as a major mechanism for the loss of viability of skeletal muscle following ischaemia and reperfusion, much less is known of the role of apoptosis. In this study rat hind limbs were subjected to 2 h of tourniquet ischaemia, then reperfused for either 0, 0.25, 0.5, 1, 3, 8, 16 or 24 h (n = 6 per group). Mean viability of muscle, assessed by tetrazolium dye reduction, after 2 h ischaemia and 24 h reperfusion was 17%. Histological examination revealed disrupted, necrotic muscle fibres from 30 min to 24 h reperfusion. Apoptotic nuclei were identified by haematoxylin staining and TUNEL, terminal deoxynucleotidyl transferase mediated dUTP nick end labelling. No TUNEL-positive cells were observed at the end of the ischaemic period, but a small number of TUNEL-positive endothelial and smooth muscle cells were found at 30 min reperfusion, with a progressive increase in their number up to 24 h reperfusion. Apoptotic neutrophils were detected after 8-24 h reperfusion. At no stage was apoptosis seen in the nuclei of skeletal muscle fibres. It appears that apoptosis plays no role in the death of muscle fibres after ischaemia-reperfusion injury to skeletal muscle.

Animals↗
PubMed1999

Control of sigma factor activity during Bacillus subtilis sporulation.

When starved, Bacillus subtilis undergoes asymmetric division to produce two cell types with different fates. The larger mother cell engulfs the smaller forespore, then nurtures it and, eventually, lyses to release a dormant, environmentally resistant spore. Driving these changes is a programme of transcriptional gene regulation. At the heart of the programme are sigma factors, which become active at different times, some only in one cell type or the other, and each directing RNA polymerase to transcribe a different set of genes. The activity of each sigma factor in the cascade is carefully regulated by multiple mechanisms. In some cases, novel proteins control both sigma factor activity and morphogenesis, co-ordinating the programme of gene expression with morphological change. These bifunctional proteins, as well as other proteins involved in sigma factor activation, and even precursors of sigma factors themselves, are targeted to critical locations, allowing the mother cell and forespore to communicate with each other and to co-ordinate their programmes of gene expression. This signalling can result in proteolytic sigma factor activation. Other mechanisms, such as an anti-sigma factor and, perhaps, proteolytic degradation, prevent sigma factors from becoming active in the wrong cell type. Accessory transcription factors modulate RNA polymerase activity at specific promoters. Negative feedback loops limit sigma factor production and facilitate the transition from one sigma factor to the next. Together, the mechanisms controlling sigma factor activity ensure that genes are expressed at the proper time and level in each cell type.

Adenosine Triphosphate↗
PubMed1999

Three-dimensional thoracic modeling for an anatomical compatibility study of the implantable total artificial heart.

Anatomical compatibility with the thoracic cavity is important in developing a completely implantable total artificial heart (TAH). The purpose of this study was to examine the optimal morphology of our TAH and to develop a computer implantation simulation environment for preoperational discussion. As the first stage, we constructed a prototype simulation system by creating a 3-D surface model of a thoracic cavity and one of a TAH. In this system, the thoracic surface model, composed of the aorta, pulmonary artery, ventricle resected heart, diaphragm, and thoracic wall, was created based on the organ contours extracted from electrocardiogram (ECG)-synchronized ultrafast computer tomographic images. The accuracy of the thoracic model was discussed using a phantom. The fitting study can be performed on the computer with the model of the thorax and that of the TAH. In the future, construction of a database for the thoracic cavities of heart failure patients is planned to improve the morphology of the TAH.

Computer Simulation↗
PubMed1999

The development of a control method for a total artificial heart using mixed venous oxygen saturation.

For physiological control of a total artificial heart (TAH), applying mixed venous oxygen saturation (SVO2) as a parameter for TAH control is a promising approach regarding sensitivity to the recipient's oxygen demand and the practical possibility of continuous monitoring using near infrared rays through transparent blood pump housings. To develop a control method for the TAH using SVO2, the relationship between SVO2 and cardiac output (CO) was investigated in a normal calf, and a control algorithm was developed based on this correlation. Then the feasibility of this method (SVO2 mode) was evaluated in a calf implanted with a pneumatic TAH and compared with the fixed drive control mode (fixed mode) in which the drive parameters were unchanged. The calf performed a graded exercise test in both modes. The CO was effectively increased from 7.3 to 13.0 L/min in the SVO2 mode, and the capacity for exercise was augmented compared to the fixed mode. We conclude that this SVO2 mode is feasible and may be effectively applied in TAH control.

Animals↗
PubMed1999

In vivo evaluation of the national cardiovascular center electrohydraulic total artificial heart.

We have been developing an electrohydraulic total artificial heart system. The system comprises an intrathoracic pumping unit composed of diaphragm type ellipsoidal blood pumps and an energy converter in addition to an electronics unit. The in vivo performance of the pumping unit was evaluated in a series of animal implantations with 3 calves weighing 62-85 kg. An interatrial shunt 4.5 mm in diameter was made in the atrial septum to compensate left-right imbalance. Two calves died early postoperatively, one of external controller power failure and the other of interatrial shunt stenosis due to thrombus formation. One calf, however, survived over 10 days under stable circulatory conditions. No abnormality was found in the oxygen metabolic condition or in major organ functions. The generation and dissipation of heat from the device was acceptable. This animal died of device malfunction caused by energy converter bearing breakdown. The device demonstrated a good anatomic fit without compromising the great vessels and adjacent tissues. It is concluded that the pumping unit has a sufficient in vivo basic performance although appropriate countermeasures are to be implemented against the detected problems concerning mechanical durability and interatrial shunt patency.

Animals↗
PubMed1999

An 18-mer peptide fragment of prosaposin ameliorates place navigation disability, cortical infarction, and retrograde thalamic degeneration in rats with focal cerebral ischemia.

It was previously reported that prosaposin possesses neurotrophic activity that is ascribed to an 18-mer peptide comprising the hydrophilic sequence of the rat saposin C domain. To evaluate the effect of the 18-mer peptide on ischemic neuronal damage, the peptide was infused in the left lateral ventricle immediately after occlusion of the left middle cerebral artery (MCA) in stroke-prone spontaneously hypertensive (SP-SH) rats. The treatment ameliorated the ischemia-induced space navigation disability and cortical infarction and prevented secondary thalamic degeneration in a dose-dependent manner. In culture experiments, treatment with the 18-mer peptide attenuated free radical-induced neuronal injury at low concentrations (0.002 to 2 pg/mL), and the peptide at higher concentrations (0.2 to 20 ng/mL) protected neurons against hypoxic insult. Furthermore, a saposin C fragment comprising the 18-mer peptide bound to synaptosomal fractions of the cerebral cortex, and this binding decreased at the 1st day after MCA occlusion and recovered to the preischemic level at the 7th day after ischemia. These findings suggest that the 18-mer peptide ameliorates neuronal damage in vivo and in vitro through binding to the functional receptor, although the cDNA encoding prosaposin receptor has not been determined yet.

Amino Acid Sequence↗
PubMed1999

Functional insights from structural predictions: analysis of the Escherichia coli genome.

Fold assignments for proteins from the Escherichia coli genome are carried out using BASIC, a profile-profile alignment algorithm, recently tested on fold recognition benchmarks and on the Mycoplasma genitalium genome and PSI BLAST, the newest generation of the de facto standard in homology search algorithms. The fold assignments are followed by automated modeling and the resulting three-dimensional models are analyzed for possible function prediction. Close to 30% of the proteins encoded in the E. coli genome can be recognized as homologous to a protein family with known structure. Most of these homologies (23% of the entire genome) can be recognized both by PSI BLAST and BASIC algorithms, but the latter recognizes an additional 260 homologies. Previous estimates suggested that only 10-15% of E. coli proteins can be characterized this way. This dramatic increase in the number of recognized homologies between E. coli proteins and structurally characterized protein families is partly due to the rapid increase of the database of known protein structures, but mostly it is due to the significant improvement in prediction algorithms. Knowing protein structure adds a new dimension to our understanding of its function and the predictions presented here can be used to predict function for uncharacterized proteins. Several examples, analyzed in more detail in this paper, include the DPS protein protecting DNA from oxidative damage (predicted to be homologous to ferritin with iron ion acting as a reducing agent) and the ahpC/tsa family of proteins, which provides resistance to various oxidating agents (predicted to be homologous to glutathione peroxidase).

Algorithms↗