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B Lorber

Publications and source records attributed to B Lorber.

At least 19 recordsLinked to original sources
PubMed2001

Crystallization and preliminary X-ray diffraction data of the second and archaebacterial-type aspartyl-tRNA synthetase from Thermus thermophilus.

The archaebacterial-type aspartyl-tRNA synthetase (AspRS2) from the thermophilic eubacterium Thermus thermophilus was crystallized using the hanging-drop vapour-diffusion method. Crystals grew at pH 9.5 in the presence of PEG 8000 and NaCl. A native diffraction data set has been collected at 2.5 A resolution using synchrotron radiation and cryocooling. Crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 57.3, b = 121.9, c = 166.9 A and V(M) = 3.03 A(3) Da(-1). There is one dimer of M(r) 96 000 per asymmetric unit. A molecular-replacement analysis gave solutions for the rotation and translation functions.

Archaea↗
PubMed2001

Growth kinetics, diffraction properties and effect of agarose on the stability of a novel crystal form of Thermus thermophilus aspartyl-tRNA synthetase-1.

Growth kinetics and diffraction properties of monoclinic crystals of eubacterial Thermus thermophilus aspartyl-tRNA synthetase-1 (AspRS-1) prepared in the presence of polyethylene glycol and agarose are studied. Their solubility and two-dimensional phase diagram are compared with those of orthorhombic crystals which grow in the presence of sodium formate or ammonium sulfate. The growth mechanism of the novel crystals was monitored by atomic force microscopy. The gel stabilizes the crystal lattice under the cryogenic conditions used for structure determination at high resolution.

Aspartate-tRNA Ligase↗
PubMed2000

The free yeast aspartyl-tRNA synthetase differs from the tRNA(Asp)-complexed enzyme by structural changes in the catalytic site, hinge region, and anticodon-binding domain.

Aminoacyl-tRNA synthetases catalyze the specific charging of amino acid residues on tRNAs. Accurate recognition of a tRNA by its synthetase is achieved through sequence and structural signalling. It has been shown that tRNAs undergo large conformational changes upon binding to enzymes, but little is known about the conformational rearrangements in tRNA-bound synthetases. To address this issue the crystal structure of the dimeric class II aspartyl-tRNA synthetase (AspRS) from yeast was solved in its free form and compared to that of the protein associated to the cognate tRNA(Asp). The use of an enzyme truncated in N terminus improved the crystal quality and allowed us to solve and refine the structure of free AspRS at 2.3 A resolution. For the first time, snapshots are available for the different macromolecular states belonging to the same tRNA aminoacylation system, comprising the free forms for tRNA and enzyme, and their complex. Overall, the synthetase is less affected by the association than the tRNA, although significant local changes occur. They concern a rotation of the anticodon binding domain and a movement in the hinge region which connects the anticodon binding and active-site domains in the AspRS subunit. The most dramatic differences are observed in two evolutionary conserved loops. Both are in the neighborhood of the catalytic site and are of importance for ligand binding. The combination of this structural analysis with mutagenesis and enzymology data points to a tRNA binding process that starts by a recognition event between the tRNA anticodon loop and the synthetase anticodon binding module.

Anticodon↗
PubMed2000

The 2.0 A crystal structure of Thermus thermophilus methionyl-tRNA synthetase reveals two RNA-binding modules.

BACKGROUND: The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. The 10 class I synthetases are considered to have in common the catalytic domain structure based on the Rossmann fold, which is totally different from the class II catalytic domain structure. The class I synthetases are further divided into three subclasses, a, b and c, according to sequence homology. No conserved structural features for tRNA recognition by class I synthetases have been established. RESULTS: We determined the crystal structure of the class Ia methionyl-tRNA synthetase (MetRS) at 2.0 A resolution, using MetRS from an extreme thermophile, Thermus thermophilus HB8. The T. thermophilus MetRS structure is in full agreement with the biochemical and genetic data from Escherichia coli MetRS. The conserved 'anticodon-binding' residues are spatially clustered on an alpha-helix-bundle domain. The Rossmann-fold and anticodon-binding domains are connected by a beta-alpha-alpha-beta-alpha topology ('SC fold') domain that contains the class I specific KMSKS motif. CONCLUSIONS: The alpha-helix-bundle domain identified in the MetRS structure is the signature of the class Ia enzymes, as it was also identified in the class Ia structures of the isoleucyl- and arginyl-tRNA synthetases. The beta-alpha-alpha-beta-alpha topology domain, which can now be identified in all known structures of the class Ia and Ib synthetases, is likely to dock with the inner side of the L-shaped tRNA, thereby positioning the anticodon stem.

Anticodon↗
PubMed2000

Revisiting the oral glucose tolerance test criterion for the diagnosis of diabetes.

OBJECTIVE: The Expert Committee on the Diagnosis and Classification of Diabetes retained the 2-hour glucose concentration on an oral glucose tolerance test of >/=11.1 mmol/L (200 mg/dL) as a criterion to diagnose diabetes. Since glycated hemoglobin levels have emerged as the best measure of long-term glycemia and an important predictor of microvascular and neuropathic complications, we evaluated the distribution of hemoglobin A1C (Hb A1C) levels in individuals who had undergone an oral glucose tolerance test to determine how well 2-hour values could identify those with normal versus increased Hb A1C levels. DESIGN: A cross-sectional analysis of 2 large data sets was performed. We cross-tabulated 2-hour glucose concentrations on an oral glucose tolerance test separated into 4 intervals (<7.8 mmol/L [140 mg/dL], 7.8-11.0 mmol/L [140-199 mg/dL], 11.1-13.3 mmol/L [200-239 mg/dL], and >/=13.3 mmol/L [240 mg/dL]) with Hb A1C levels separated into 3 intervals (normal; <1% above the upper limit of normal; and greater than or equal to the upper limit of normal + 1%). RESULTS: Approximately two thirds of patients in both data sets with 2-hour glucose concentrations of 11.1 to 13.3 mmol/L (200-239 mg/dL) had normal Hb A1C levels. In contrast, 60% to 80% of patients in both data sets with 2-hour glucose concentrations >/=13.3 mmol/L (240 mg/dL) had elevated Hb A1C levels. CONCLUSION: Since Hb A1C levels are the best measures presently available that reflect long-term glycemia, we conclude that the 2-hour glucose concentration criterion on an oral glucose tolerance test for the diagnosis of diabetes should be raised from >/= 11.1 mmol/L (200 mg/dL) to >/= 13.3 mmol/L (240 mg/dL) to remain faithful to the concept that diagnostic concentrations of glucose should predict the subsequent development of specific diabetic complications (e.g., retinopathy).

Blood Glucose↗
PubMed1999

Relationship between fasting plasma glucose and glycosylated hemoglobin: potential for false-positive diagnoses of type 2 diabetes using new diagnostic criteria.

CONTEXT: New criteria for the diagnosis of type 2 diabetes mellitus have recently been introduced that lowered the diagnostic fasting plasma glucose (FPG) concentration from 7.8 to 7.0 mmol/L (140 to 126 mg/dL). OBJECTIVE: To determine if individuals with diabetes diagnosed by the new FPG concentration criterion would have excessive glycosylation (elevated hemoglobin [HbA1c] levels). DEFINITIONS: We determined the distribution of HbA1c levels in individuals using 4 classifications: (1) normal by the new criterion (FPG concentration <6.1 mmol/L [110 mg/dL]); (2) impaired fasting glucose by the new criterion (FPG concentration of 6.1-6.9 mmol/L [110-125 mg/dL]); (3) diabetes diagnosed solely by the new FPG concentration criterion of 7.0 through 7.7 mmol/L (126-139 mg/dL); and (4) diabetes diagnosed by the previous FPG concentration criterion of 7.8 mmol/L (140 mg/dL) or higher. DESIGN: Cross-sectional analysis of 2 large data sets (NHANES III and Meta-Analysis Research Group [MRG] on the Diagnosis of Diabetes Using Glycated Hemoglobin) that contained individuals in whom FPG concentrations, 2-hour glucose concentrations using an oral glucose tolerance test, and an HbA1c level were simultaneously measured. We cross-tabulated FPG concentrations (<6.1 mmol/L [110 mg/dL], 6.1-6.9 mmol/L [110-125 mg/dL], 7.0-7.7 mmol/L [126-139 mg/dL], and > or =7.8 mmol/L [140 mg/dL]) and HbA1c levels separated into 3 intervals: normal, less than the upper limit of normal (ULN); slightly elevated, ULN to ULN plus 1%; and high, higher than ULN plus 1%. RESULTS: Among subjects with normal FPG concentrations, HbA1c levels in the NHANES III (and the MRG) data sets were normal in 97.3% (96.2%), slightly elevated in 2.7% (3.6%), and high in 0.1% (0.2%). Among individuals with impaired fasting glucose, HbA1c concentrations were normal in 86.7% (81.4%), slightly elevated in 13.1% (16.4%), and high in 0.2% (2.2%). Among diabetic patients diagnosed by the new FPG criterion only, HbA1c levels were normal in 60.9% (59.6%), slightly elevated in 35.8% (32.8%), and high in 3.4% (7.6%). In diabetic patients diagnosed by the former FPG criterion, HbA1c levels were normal in 18.6% (16.7%), slightly elevated in 32.5% (21.0%), and high in 48.9% (62.3%). CONCLUSIONS: About 60% of the new cohort of diabetic patients in both data sets have normal HbA1c levels. We believe that diabetes should not be diagnosed in those with FPG concentrations less than 7.8 mmol/L (140 mg/dL) unless excessive glycosylation is evident. Individuals without excessive glycosylation but with moderate elevations of FPG concentrations (6.1-7.7 mmol/L [110-139 mg/dL]) should be diagnosed as having impaired fasting glucose and treated with an appropriate diet and exercise. This diagnostic labeling achieves the goal of early intervention without subjecting these persons to the potentially negative insurance, employment, social, and psychological consequences of a diagnosis of diabetes mellitus.

Adult↗
PubMed1999

Crystallogenesis studies on yeast aspartyl-tRNA synthetase: use of phase diagram to improve crystal quality.

Aspartyl-tRNA synthetase (AspRS) extracted from yeast is heterogeneous owing to proteolysis of its positively charged N-terminus; its crystals are of poor quality. To overcome this drawback, a rational strategy was developed to grow crystals of sufficient quality for structure determination. The strategy is based on improvement of the protein homogeneity and optimization of crystallization, taking advantage of predictions from crystal-growth theories. An active mutant lacking the first 70 residues was produced and initial crystallization conditions searched. The shape and habit of initial crystals were improved by establishing a phase diagram of protein versus crystallizing-agent concentrations. Growth of large well faceted crystals takes place at low supersaturations near the isochronic supersolubility curve. Further refinement led to reproducible growth of two crystalline forms of bipyramidal (I) or prismatic (II) habit. Both diffract X-rays better than crystals previously obtained with native AspRS. Complete data sets were collected at 3 A resolution for form I (space group P41212) and form II (space group P3221) and molecular-replacement solutions were found in both space groups.

Aspartate-tRNA Ligase↗
PubMed1999

Polymorphism of turnip yellow mosaic virus empty shells and evidence for conformational changes occurring after release of the viral RNA. A differential scanning calorimetric study.

Turnip yellow mosaic virus (TYMV) is a small isometric plant virus which decapsidates by releasing its RNA through a hole in the capsid, leaving behind an empty shell [R. E. F. Matthews and J. Witz, (1985) Virology 144, 318-327]. Similar empty shells (artificial top component, ATC) can be obtained by submitting the virions to various treatments in vitro. We have used differential scanning calorimetry, analytical sedimentation, and electron microscopy to investigate the thermodenaturation of natural empty shells (NTC, natural top component) present in purified virus suspensions, and of several types of ATCs. ATCs divided in two major classes. Those obtained by alkaline titration, by the action of urea or butanol behaved as NTC: their thermograms contained only one peak corresponding to the irreversible dissociation of the shells and the denaturation of the coat protein. The temperature of this unique transition varied significantly with pH, from 71 degrees C at pH 4.5 to 84 degrees C at pH 8.5. The thermograms of ATCs obtained by freezing and thawing, or by the action of high pressure, contained two peaks: shells dissociated first into smaller protein aggregates at 57 degrees C (at pH 5.0) to 61 degrees C (at pH 8.5), which denatured at the temperature of the unique transition of NTC. Shells obtained by heating virions to 55 degrees C at pH 7.6, changed conformation after the release of the viral RNA, as upon continuous heating to 95 degrees C, their thermograms were similar to those of the shells obtained by freezing and thawing, whereas after purification they behaved like NTC. Structural implications of these observations are discussed.

Calorimetry, Differential Scanning↗
PubMed1999

Crystallization within agarose gel in microgravity improves the quality of thaumatin crystals.

To prevent crystals from moving in orbit and sedimenting upon their return to earth, the model protein thaumatin was crystallized in agarose gel in the Advanced Protein Crystallization Facility during the eight-day Space Shuttle mission STS-95 (November 1998). The quality of tetragonal crystals grown in microgravity was compared with that of controls prepared in parallel in the laboratory. On the basis of their diffraction properties, microgravity crystals were more ordered than crystals grown in gel on earth (the latter being, on average, better than reference crystals obtained in solution on earth). It is concluded that protein crystallization within a gel in microgravity may yield crystals of superior quality by combining the advantages of both environments. A possible explanation for the positive effect of microgravity on protein crystallization in gels involving the better quality of the nucleus is discussed.

Crystallization↗
PubMed1997

Comparative analysis of thaumatin crystals grown on earth and in microgravity.

The protein thaumatin was studied as a model macro-molecule for crystallization in microgravity-environment experiments conducted on two US Space Shuttle missions (USML-2 and LMS). In this investigation, we have evaluated and compared the quality of space- and earth-grown thaumatin crystals using X-ray diffraction analyses, and characterized them according to crystal size, diffraction resolution limit and mosaicity. Two different approaches for growing thaumatin crystals in the microgravity environment, dialysis and liquid-liquid diffusion, were employed as a joint experiment by our two investigative teams. Thaumatin crystals grown in a microgravity environment were generally larger in volume and the total number of crystals was less, relative to crystals grown on earth. They diffracted to significantly higher resolution and with improved diffraction properties, as judged by relative plots of I/sigma versus resolution. The mosaicity of space-grown crystals was significantly less than that of crystals grown on earth. Increased concentrations of protein in the crystallization chambers in microgravity led to larger crystals. The data presented here lend further support to the idea that protein crystals of improved quality can be obtained in a microgravity environment.

Crystallization↗
PubMed1997

Over-the-counter and alternative medicines in the treatment of chronic vaginal symptoms.

OBJECTIVE: To investigate the use of over-the-counter and alternative medicines in women with chronic vaginal symptoms. METHODS: One hundred five patients, referred by their gynecologists for evaluation of chronic vaginal symptoms, were interviewed about their use of over-the-counter and alternative medicines during the preceding year, the amount of money spent on each, and whether or not their physicians had been informed of these treatments. RESULTS: The mean age was 36 years, and one-half had finished college. The median symptom duration was 2 years. Seventy-seven (73.3%) patients had self-treated with over-the-counter medications such as miconazole (74% of over-the-counter users), clotrimazole (38.2%), or povidone-iodine (13.2%). The median expenditure for over-the-counter use was %0 (range $2-1000). Forty-four (41.9%) had used alternative medicines, most frequently acidophilus pills orally (50%) vaginally (11.4%), yogurt orally (20.5%) or vaginally (18.2%), vinegar douches (13.6%), and boric acid (13.6%). The median expenditure for alternative medicines was $35 (range $0-1200). Fewer physicians were aware of the use of alternative (70.5%) that of over-the-counter medicines (88.3%). Although most patients thought that vulvovaginal candidiasis was the cause of their symptoms, the most common diagnoses at initial presentation were candidiasis in 29 (27.6%), vulvar vestibulitis in 18 (17.1%), irritant dermatitis in 16 (15.2%), and bacterial vaginosis in 11 (10.5%). Women who actually had candidiasis were more likely to have used alternative medicines (odds ration 2.31, 95% confidence interval 1.00, 5.42) than other patients. CONCLUSION: Women with chronic vaginal symptoms often use over-the-counter and alternative medicines that add to health care costs and are unlikely to be of benefit.

Adult↗
PubMed1997

Use and effectiveness of hypothermia blankets for febrile patients in the intensive care unit.

We performed a prospective observational (noninterventional) study of hypothermia blanket use in a population of adult intensive care unit patients with body temperatures of > or = 102.5 degrees F. Thirty-nine of ninety-four febrile episodes (in 83 patients) were treated with hypothermia blankets. Logistic regression revealed that the strongest independent predictors of hypothermia blanket use were a temperature of > or = 103.5 degrees F (odds ratio [OR] = 17), mechanical ventilation (OR = 25), and acute central nervous system illness (OR = 7.5). Hospitalization in the medical intensive care unit was strongly associated with avoidance of this therapy (OR = 0.023). Treatment with a hypothermia blanket was ordered by a physician in only 15% of cases. The mean cooling rate was the same (0.028 degree F/h) for blanket-treated and control patients. Multivariate Cox regression and factorial and repeated measures of analysis of variance revealed that blanket treatment was not more effective than other cooling methods. However, this treatment was associated with more "zigzag" temperature fluctuations of > or = 3 degrees F (56% of blanket-treated patients vs. 18% of control patients; P < .001) and rebound hypothermia (18% vs. 0; P = .001). Hypothermia blanket therapy is primarily a nursing decision. We conclude that in addition to being no more effective than other cooling measures, hypothermia blanket therapy was associated with more temperature fluctuations and with more episodes of rebound hypothermia.

Adult↗
PubMed1997

Listeriosis.

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Acquired Immunodeficiency Syndrome↗
PubMed1996

Are all diseases infectious?

The complex interactions between microorganisms and human hosts include the well-known, traditional infectious diseases and the symbiotic relation we have with our normal flora. The media have brought to the public's attention many newly described infectious diseases, such as Ebola virus hemorrhagic fever, that were not part of common medical parlance a decade ago. While flooding us with interesting and often dramatic reports of so-called emerging infectious diseases, the media have largely ignored a more fundamental change in our appreciation of human-microorganism interactions: the discovery that transmissible agents may play important roles in diseases not suspected of being infectious in origin. A well-known example is ulcer disease; other examples include neurodegenerative disease, inflammatory disease, and cancer. These fascinating instances of host-pathogen interaction open new prospects for the prevention of disease through immunization.

Disease↗