Search PubMed⌕ Search

Biomedical subjects

Y Cao

Publications and source records attributed to Y Cao.

At least 469 records · Page 26Linked to original sources
PubMed1993

Genotypic and phenotypic characterization of HIV-1 patients with primary infection.

Better characterization of human immunodeficiency virus-type 1 (HIV-1) in patients with primary infection has important implications for the development of an acquired immunodeficiency syndrome (AIDS) vaccine because vaccine strategies should target viral isolates with the properties of transmitted viruses. In five HIV-1 seroconverters, the viral phenotype was found to be uniformly macrophage-tropic and non-syncytium-inducing. Furthermore, the viruses were genotypically homogeneous within each patient, but a common signature sequence was not discernible among transmitted viruses. In the two cases where the sexual partners were also studied, the sequences of the transmitted viruses matched best with minor variants in the blood of the transmitters. There was also a stronger pressure to conserve sequences in gp120 than in gp41, nef, and p17, suggesting that a selective mechanism is involved in transmission.

Amino Acid Sequence↗
PubMed1993

Pathway of proton uptake in the bacteriorhodopsin photocycle.

The time courses of chromophore reactions and proton uptake in the second half of the photocycle of the proton pump bacteriorhodopsin (BR) were examined. At pH > 8.5, the kinetics are simplified by the fact that only the M and N intermediates accumulate. The relaxation kinetics after perturbation of M with a second, blue flash confirm that M<==>N equilibration is the only significant cause of the biphasic M decay. With this feature, the analysis of time-resolved difference spectra yields a scheme which contains two sequential N states connected by a nearly unidirectional reaction. The proton uptake from the bulk, as measured with the pH-indicator dye pyranine, occurs during the decay of the first N rather than the recovery of BR. The results thus suggest the model M2(-1)<==>N(-1) + H+ (from the bulk)<==>N(0)-->BR, where the superscripts indicate the protonation state of the protein relative to BR. M2(-1)-->N(-1) is reprotonation of the Schiff base from D96, N(-1) + H+ (from the bulk)-->N(0) is uptake of proton from the cytoplasmic side, and N(0)-->BR represents 13-cis to all-trans reisomerization of the retinal and other relaxations which regenerate the initial state. R227, a residue near D96, affects the deprotonation of D96 more than the subsequent proton uptake. According to the changed [M2(-1)]/[N(-1)] equilibrium in the R227Q protein, interaction between R227 and D96 is responsible for about 1 pH unit of the decrease in the pKa of D96 during the reprotonation of the Schiff base. According to the pH dependencies of the rate constants in the N(-1)<==>N(0) equilibrium in wild-type and R227Q, interaction with R227 lowers the pKa for proton uptake from the bulk by 0.5 pH unit, to 11. We conclude from the proton uptake kinetics that at physiological pH free energy is converted to proton electrochemical potential in this pump not only as protons are released on the extracellular side [Zimányi, L., Váró. G., Chang, M., Ni, B., Needleman, R., & Lanyi, J. K. (1992) Biochemistry 31, 8535-8543] but also as protons are taken up on the cytoplasmic side.

Bacteriorhodopsins↗
PubMed1993

Characterization of rabbit skeletal muscle glycogenin. Tyrosine 194 is essential for function.

The biogenesis of glycogen involves a specific initiation event mediated by the initiator protein, glycogenin, which undergoes self-glucosylation to generate an oligosaccharide primer from which the glycogen molecule grows. Rabbit muscle glycogenin was expressed at high levels in Escherichia coli and purified close to homogeneity in a procedure that involved binding to a UDP-agarose affinity column. The resulting protein had subunit molecular weight of 38,000 as judged by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Analysis of peptide fragments by mass spectroscopy indicated that the recombinant glycogenin was already glucosylated at Tyr-194 and contained from 1 to 8 glucose residues attached. The enzyme was active as a glucosyl transferase and could incorporate a further approximately 5 mol of glucose/mol. The apparent Km for the glucosyl donor UDP-glucose was 4.5 microM, and the pH optimum was pH 8. Of a number of nucleotides and related compounds surveyed, UDP and UTP were the most effective inhibitors. There was also a correlation between inhibition and the presence of a pyrophosphate group. Of several oligosaccharides of glucose, only maltose caused significant inhibition. The glucosylation reaction was first order with respect to glycogenin suggesting that it was intramolecular. The efficacy of the purified glycogenin as a substrate for the elongation reaction catalyzed by glycogen synthase was significantly enhanced if glycogenin was first allowed to undergo self-glucosylation. The length of the priming oligosaccharide is thus important for glycogen synthase action. A mutant of glycogenin, in which Tyr-194 was changed to Phe, behaved identically to the wild-type through purification and in particular bound to the UDP-agarose affinity matrix. Despite these indications of the protein's overall structural integrity, it was unable to self-glucosylate. This result indicates that Tyr-194 is necessary for glycogenin function and is consistent with Tyr-194 being the sole site of glucosylation.

Amino Acid Sequence↗
PubMed1993

Glucose control of rabbit skeletal muscle glycogenin expressed in COS cells.

Glycogenin is a self-glucosylating protein involved in the initiation of glycogen synthesis. Rabbit skeletal muscle glycogenin, transiently expressed in COS cells, was found exclusively in the low speed supernatant fraction, with M(r) 37-38,000. The protein was capable of self-glucosylation and was, if suitably primed, an effective substrate for glycogen synthase. Rabbit muscle glycogen synthase was similarly expressed, to a level 7-10-fold over the endogenous activity. Most of the expressed protein was found in the low speed pellet fraction. However, when co-expressed with glycogenin, a significant increase in the proportion of glycogen synthase in the soluble fraction was observed. Therefore, glycogenin interacts with glycogen synthase in the cell and redistributes the synthase to the soluble fraction. Co-expression of an inactive form of glycogenin did not affect glycogen synthase localization. The expressed glycogenin could be detected as two distinguishable species, differing slightly in electrophoretic mobility, depending on the glucose concentration of the cell culture medium. At 25 mM glucose, a form of M(r) 38,000 was observed; however, upon transfer to 5 mM glucose, it converted to a species of slightly lower M(r). The M(r) of the 38,000-dalton species could be also be reduced by treatment of the cell extract with alpha-amylase. It was additionally found that the 38,000-dalton glycogenin was a much more effective glycogen synthase substrate than the lower M(r) species. These results, therefore, raise the possibility of a novel mechanism for the control of glycogen metabolism in which glucose levels would regulate the glucosylation state of glycogenin, which in turn would determine glycogenin's efficacy as a substrate for elongation by glycogen synthase.

Animals↗
PubMed1993

Pentylenetetrazol seizures increase pro-nerve growth factor-like immunoreactivity in the reticular thalamic nucleus and nerve growth factor mRNA in the dentate gyrus.

Neurotrophins may have a neuroprotective role and are probably involved in the control of axonal sprouting and synaptic plasticity. An antibody raised against a pro-sequence of nerve growth factor (NGF) was tested. In control undisturbed rats, a strong immunoreactivity was detected in scattered cells in and around the pyramidal and granule cell layer of the hippocampus and a moderate labeling was found in the reticular thalamic nucleus. In situ hybridization showed specific expression of NGF mRNA in a similar population of scattered cells in the hippocampal formation but not in the reticular thalamic nucleus. Acute epileptic seizures, induced by a convulsive dose of 50 mg/kg pentylenetetrazol (PTZ), strongly increased NGF mRNA in neurons of the granular layer of the dentate gyrus 3 hr but not 6 hr after the injection. No change in pro-NGF-like immunoreactivity was observed in the hippocampus or reticular thalamic nucleus after acute seizures. Chemical kindling was induced by daily injections of subconvulsive doses (30 mg/kg) of PTZ for 4 weeks. This treatment significantly increased pro-NGF-like immunoreactivity in the reticular thalamic nucleus but did not affect NGF mRNA. These data strengthen a role for the reticular thalamic nucleus and NGF in PTZ kindling.

Amino Acid Sequence↗
PubMed1993

Proton transfer from Asp-96 to the bacteriorhodopsin Schiff base is caused by a decrease of the pKa of Asp-96 which follows a protein backbone conformational change.

In the bacteriorhodopsin photocycle the transported proton crosses the major part of the hydrophobic barrier during the M to N reaction; in this step the Schiff base near the middle of the protein is reprotonated from D96 located near the cytoplasmic surface. In the recombinant D212N protein at pH > 6, the Schiff base remains protonated throughout the photocycle [Needleman, Chang, Ni, Váró, Fornés, White, & Lanyi (1991) J. Biol. Chem. 266, 11478-11484]. Time-resolved difference spectra in the visible and infrared are described by the kinetic scheme BR-->K<==>L<==>N (-->N')-->BR. As evidenced by the large negative 1742-cm-1 band of the COOH group of the carboxylic acid, deprotonation of D96 in the N state takes place in spite of the absence of the unprotonated Schiff base acceptor group of the M intermediate. Instead of internal proton transfer to the Schiff base, the proton is released to the bulk, and can be detected with the indicator dye pyranine during the accumulation of N'. The D212N/D96N protein has a similar photocycle, but no proton is released. As in wild-type, deprotonation of D96 in the N state is accompanied by a protein backbone conformational change indicated by characteristic amide I and II bands. In D212N the residue D96 can thus deprotonate independent of the Schiff base, but perhaps dependent on the detected protein conformational change. This could occur through increased charge interaction between D96 and R227 and/or increased hydration near D96. We suggest that the proton transfer from D96 to the Schiff base in the wild-type photocycle is driven also by such a decrease in the pKa of D96.

Amino Acid Sequence↗
PubMed1993

Idiopathic CD4+ T-lymphocytopenia--immunodeficiency without evidence of HIV infection.

BACKGROUND: The human immunodeficiency virus (HIV), the etiologic agent of the acquired immunodeficiency syndrome (AIDS), infects and depletes CD4+ T lymphocytes. Recently, patients have been described with profound CD4+ T-lymphocytopenia but without evident HIV infection, a condition now termed idiopathic CD4+ T-lymphocytopenia, and a national surveillance network has been set up to investigate such cases. METHODS: We studied 12 patients with CD4+ T-lymphocytopenia who were referred to us from three U.S. cities. Blood samples were tested for HIV with specific antibody assays, viral cultures, and polymerase-chain-reaction (PCR) techniques. RESULTS: The patients (10 men and 2 women) ranged in age from 30 to 69 years. Eight had risk factors for HIV infection. The clinical manifestations were heterogeneous: five patients had opportunistic infections, five had syndromes of unknown cause, and two had no symptoms. Two patients died from acute complications of their immunodeficiency. The patients' lowest CD4+ lymphocyte counts ranged from 3 to 308 per cubic millimeter (mean, 149). Three patients had complete or partial spontaneous reversal of the CD4+ T-lymphocytopenia. Concomitant CD8+ T-lymphocytopenia was noted in three patients, and abnormal immunoglobulin levels were found in five. Multiple virologic studies by serologic testing, culture, and PCR were completely negative for HIV in all patients. CONCLUSIONS: Our 12 patients with idiopathic CD4+ T-lymphocytopenia appear to be epidemiologically, clinically, and immunologically heterogeneous. It is unclear whether this syndrome is new, transmissible, or acquired. Many of the clinical and immunologic features are distinct from those found in AIDS, and our extensive virologic studies found no evidence of HIV infection. The cause of this condition remains unknown.

Adult↗
PubMed1993

Feature-recognizing MRI.

We describe a new theory of MR imaging that utilizes prior information in the form of a set of "training" images thought to be similar to the "unknown" objects to be scanned. First, the training images are processed to find an orthonormal series representation of these images that is more convergent than the usual Fourier series. The coefficients in this new series can be calculated from a subset of the phase-encoded signals needed to construct the Fourier image representation. The characteristics of the training images also determine exactly which phase-encoded signals should be measured in order to minimize error in the image reconstruction. The optimal phase-encodings are usually scattered nonuniformly in kappa-space. Good results were obtained when this theory was applied to imaging data from simulated objects and to experimental data from phantom scans. This theory provides the basis for developing efficient scanning and image reconstruction techniques that are "tailored" to each body part or to particular disease states.

Algorithms↗
PubMed1993

Tempo and mode of mitochondrial DNA evolution in vertebrates at the amino acid sequence level: rapid evolution in warm-blooded vertebrates.

By using complete sequence data of mitochondrial DNAs, three Markov models (Dayhoff, Proportional, and Poisson models) for amino acid substitutions during evolution were applied in maximum likelihood analyses of mitochondrially encoded proteins to estimate a phylogenetic tree depicting human, cow, whale, and murids (mouse and rat), with chicken, frog, and carp as outgroups. A cow/whale clade was confirmed with a more than 99.8% confidence level by any of the three models, but the branching order among human, murids, and the cow/whale clade remained uncertain. It turned out that the Dayhoff model is by far the most appropriate model among the alternatives in approximating the amino acid substitutions of mitochondrially encoded proteins, which is consistent with a previous analysis of a more limited data set. It was shown that the substitution rate of mitochondrially encoded proteins has increased in the order of fishes, amphibians, birds, and mammals and that the rate in mammals is at least six times, probably an order of magnitude, higher than that in fishes. The higher evolutionary rate in birds and mammals than in amphibians and fishes was attributed to relaxation of selective constraints operating on proteins in warm-blooded vertebrates and to high mutation rate of bird and mammalian mitochondrial DNAs.

Amino Acid Sequence↗
PubMed1993

Periodic crystallization effect in the surface layers of coatings during plasma spraying of hydroxyapatite.

A new effect of the amorphous component of periodic crystallization in the surface layers of coatings during hydroxyapatite (HA) plasma spraying is revealed. The effect is caused by significant temperature increases of surface layers due to plasma heating in the process of coating. Under prevalent spraying conditions, the crystallite sizes of the crystallite phase are considerably less than those in dense HA. These non-equilibrium phases crystallize consistently and, as a result, in the surface layers HA crystallites emerge and grow. This leads to oscillating type dependences of crystallite size and crystallinity on coating thickness.

Biocompatible Materials↗
PubMed1993

Integrated 3D display of brain surface anatomy and MR spectral data.

We describe a method of displaying the relationship between MR spectral data and an MRI-derived three-dimensional (3D) model of the same subject's brain surface. In this way, biochemical abnormalities in the MR spectra can be localized with respect to specific gyral convolutions (e.g., those associated with movement and sensation), which are best identified on 3D brain models. This was accomplished by retrospectively registering spectral data and MR images, acquired with different head coils. The highly resolved MR images were used to identify the brain surface in the poorly resolved spectral data and to produce a 3D rendition of brain surface metabolite distributions. This was then integrated with an MRI-derived 3D model of brain gyral anatomy. The method was tested on P31 spectral data from a phantom and from a human volunteer.

Adult↗
PubMed1993

Adaptation of two primary human immunodeficiency virus type 1 isolates to growth in transformed T cell lines correlates with alterations in the responses of their envelope glycoproteins to soluble CD4.

Two sCD4-resistant, primary viruses (P-08 and P-17) were compared with two sCD4-sensitive, T cell line-adapted variants (C-08 and C-17) for their biochemical responses to sCD4. At 37 degrees C, neither primary virus shed gp120 within 8 hr at sCD4 concentrations of up to 500 nM, whereas C-08 and C-17 lost gp120 within minutes of addition of 5-10 nM sCD4. At 4 degrees C, however, P-17 and C-17 shed gp120 at similar rates in response to the same sCD4 concentration. Irrespective of the temperature, gp120 dissociation from both P-17 and C-17 was inhibited by CD4 MAbs 6H10 and 5A8, the latter of which blocks events subsequent to sCD4 binding. Binding of sCD4 to P-17 was greater at 4 degrees C than at 37 degrees C, whereas the converse was found for C-17. Consistent with this, P-17 was neutralized much more potently by sCD4 at 4 degrees C than at 37 degrees C, whereas C-17 was slightly more sensitive to sCD4 at 37 degrees C than at 4 degrees C. Resistance to neutralization by sCD4 is probably determined by kinetic parameters. We suggest that the acquisition of sCD4 neutralization sensitivity and the above biochemical responses to sCD4 are coincidental to the process by which some primary viruses adapt to growth in transformed T cells. Sequence data indicate that there are a limited number of amino acid differences between the Env glycoproteins of the primary viruses and their T cell line-adapted counterparts; the significance of the individual changes is under investigation, but both pairs of viruses have amino acid substitutions in a region of gp41 thought to contact gp120.

Adaptation, Biological↗
PubMed1993

Biological cloning of functionally diverse quasispecies of HIV-1.

Twenty putative clones of HIV-1, derived by biological cloning from two different individuals, were characterized in vitro for functional activity and genotypic diversity. Many of the biological clones isolated by this method were genetically distinct, and could be further distinguished by differences in replication kinetics, host cell range, and/or cytopathicity. Our findings indicate that biological cloning by limiting dilution cultures is an effective method for isolating replication-competent, functionally diverse quasispecies of HIV-1.

Amino Acid Sequence↗
PubMed1993

Aberrations of p53 gene in human hepatocellular carcinoma from China.

Allele losses and mutations have been examined in 38 cases of primary hepatocellular carcinomas (HCC) from different geographic areas of China by Southern, single-strand conformational polymorphism (SSCP) and direct DNA sequencing analyses. Two of 12 samples from Qi-Dong and six of 18 HCCs from Shanghai showed loss of heterozygosity (LOH) at the loci on chromosome 17p13.3. All of the nine mutations in the p53 gene detected in HCC from Qi-Dong were clustered at the third base of codon 249, i.e. G:C to T:A, leading to an arginine to serine change. In contrast, 18 HCC samples from Shanghai contained three mutations at codons 249, 255 and 279. These results suggested a relationship between the spectrum of p53 aberration and environmental risk factors in these two geographic areas. Since no correlation between the state of HBV DNA and p53 aberration was observed, other factors such as dietary exposure to aflatoxin B1 (AFB1) might be responsible for the mutational hotspot at codon 249 in HCCs from Qi-Dong area.

Aflatoxin B1↗