PubMed Health⌕ Search

Biomedical subjects

W S Lewis

Publications and source records attributed to W S Lewis.

At least 19 recordsLinked to original sources
PubMed2002

A pulsating auroral X-ray hot spot on Jupiter.

Jupiter's X-ray aurora has been thought to be excited by energetic sulphur and oxygen ions precipitating from the inner magnetosphere into the planet's polar regions. Here we report high-spatial-resolution observations that demonstrate that most of Jupiter's northern auroral X-rays come from a 'hot spot' located significantly poleward of the latitudes connected to the inner magnetosphere. The hot spot seems to be fixed in magnetic latitude and longitude and occurs in a region where anomalous infrared and ultraviolet emissions have also been observed. We infer from the data that the particles that excite the aurora originate in the outer magnetosphere. The hot spot X-rays pulsate with an approximately 45-min period, a period similar to that reported for high-latitude radio and energetic electron bursts observed by near-Jupiter spacecraft. These results invalidate the idea that jovian auroral X-ray emissions are mainly excited by steady precipitation of energetic heavy ions from the inner magnetosphere. Instead, the X-rays seem to result from currently unexplained processes in the outer magnetosphere that produce highly localized and highly variable emissions over an extremely wide range of wavelengths.

Journal Article↗
PubMed2001

Defining the molecular basis of Arf and Hdm2 interactions.

Understanding the interaction of Arf and Hdm2 has recently become a central issue in cancer biology. In response to hyperproliferative signals, p14(Arf) stabilizes p53 by binding to Hdm2 and inhibits the ubiquitination and subsequent proteosome-dependent degradation of p53. The medical importance of the Arf-Hdm2-p53 regulatory system is highlighted by the finding that either p53 or p14(Arf) are lost or modified in virtually all human cancers. Isolated Arf and Hdm2 domains are dynamically disordered in solution, yet they retain the ability to interact in vitro and in cellular assays. Upon binding, domains of both Arf and Hdm2 undergo a dramatic transition from disordered conformations to extended structures comprised of beta-strands. The presence of domains from both proteins are necessary and sufficient for the formation of the highly stable extended beta structures. We have mapped sites within Arf and Hdm2 that interact at a resolution of five amino acid residues using surface plasmon resonance. Surface plasmon resonance and circular dichroism spectropolarimetry confirm the presence of multiple interaction domains within each protein. Both p14(Arf) (human) and p19(Arf) (mouse) interact with Hdm2 through two short motifs present in their N termini. The Arf interacting region of Hdm2 is also composed of two short sequences located in the central acidic domain, between residues 235-264 and 270-289. The binding-induced structural transition is also induced by short peptides, 15 amino acids in length, that contain the binding motifs. Micro-injection and live cell imaging of proteins tagged with fluorescent labels was used to confirm the in vivo function of the interaction domains. Arf and Hdm2 thus appear to interact through a novel mechanism that exerts control over the cell division cycle. The novel molecular mechanism of interaction and the limited size of the protein domains involved provide opportunities for the development of anticancer therapeutics.

3T3 Cells↗
PubMed2001

An auroral flare at Jupiter.

Jupiter's aurora is the most powerful in the Solar System. It is powered largely by energy extracted from planetary rotation, although there seems also to be a contribution from the solar wind. This contrasts with Earth's aurora, which is generated through the interaction of the solar wind with the magnetosphere. The major features of Jupiter's aurora (based on far-ultraviolet, near-infrared and visible-wavelength observations) include a main oval that generally corotates with the planet and a region of patchy, diffuse emission inside the oval on Jupiter's dusk side. Here we report the discovery of a rapidly evolving, very bright and localized emission poleward of the northern main oval, in a region connected magnetically to Jupiter's outer magnetosphere. The intensity of the emission increased by a factor of 30 within 70 s, and then decreased on a similar timescale, all captured during a single four-minute exposure. This type of flaring emission has not previously been reported for Jupiter (similar, but smaller, transient events have been observed at Earth), and it may be related directly to changes in the solar wind.

Journal Article↗
PubMed1997

Comparison of the protection of cells from antifolates by transduced human dihydrofolate reductase mutants.

Retroviral transduction of antifolate-resistant variants of human dihydrofolate reductase (hDHFR) into cells can increase their resistance to the cytotoxic effects of these drugs. We evaluated the ability of wild-type hDHFR and 20 mutant enzymes (13 with single-amino acid substitutions, 7 with two substitutions) to prevent growth inhibition in antifolate-treated CCRF-CEM cells. The wild-type enzyme and all of the variants significantly protected transduced cells from trimetrexate (TMTX)-induced growth inhibition. However, only half of the variants conferred more protection than does the wild-type enzyme. For the variants tested, the observed protective effect was higher for TMTX than for methotrexate (< or =7.5-fold increased resistance), piritrexim (< or =16-fold), and edatrexate (negligible). Transduction of the variants L22Y-F31S and L22Y-F31R led to the greatest protection against TMTX (approximately 200-fold). Protection from loss of cell viability was similar to protection from growth inhibition. The protection associated with a particular mutant hDHFR did not result from the level of expression: Efficient protection resulted from low affinity of the variant for antifolates, reasonable catalytic activity, and good thermal stability. Clones isolated from a polyclonal population of transduced cells varied by as much as 30-fold in their resistance to TMTX, the resistance differences depending on hDHFR expression levels.

Aminopterin↗
PubMed1995

Methotrexate-resistant variants of human dihydrofolate reductase with substitutions of leucine 22. Kinetics, crystallography, and potential as selectable markers.

Although substitution of tyrosine, phenylalanine, tryptophan, or arginine for leucine 22 in human dihydrofolate reductase greatly slows hydride transfer, there is little loss in overall activity (kcat) at pH 7.65 (except for the arginine 22 variant), but Km for dihydrofolate and NADPH are increased significantly. The greatest effect, decreased binding of methotrexate to the enzyme-NADPH complex by 740- to 28,000-fold due to a large increase in the rate of methotrexate dissociation, makes these variants suitable to act as selectable markers. Affinities for four other inhibitors are also greatly decreased. Binding of methotrexate to apoenzyme is decreased much less (decreases as much as 120-fold), binding of tetrahydrofolate is decreased as much as 23-fold, and binding of dihydrofolate is decreased little or increased. Crystal structures of ternary complexes of three of the variants show that the mutations cause little perturbation of the protein backbone, of side chains of other active site residues, or of bound inhibitor. The largest structural deviations occur in the ternary complex of the arginine variant at residues 21-27 and in the orientation of the methotrexate. Tyrosine 22 and arginine 22 relieve short contacts to methotrexate and NADPH by occupying low probability conformations, but this is unnecessary for phenylalanine 22 in the piritrexim complex.

Amino Acid Sequence↗
PubMed1994

Management of traumatic facial nerve paralysis with carotid artery cavernous sinus fistula.

Massive skull base injuries require detailed preoperative neurological and neurovascular assessment prior to undertaking surgical repair of isolated cranial nerve deficits. We present the management of a patient with traumatic facial paralysis, cerebrospinal fluid leak, and carotid artery cavernous sinus fistula as the result of a gunshot wound to the skull base. The carotid artery cavernous sinus fistula was ultimately controlled with super-selective embolization via the vertebral artery. The facial nerve injury was then safely treated with mobilization of the labyrinthine and vertical segments to allow a primary anastomosis.

Adult↗
PubMed1993

Hearing preservation in cerebellopontine angle tumor surgery: the NYU experience 1974-1991.

Between 1974 and 1991, hearing preservation surgery was attempted on 161 of 476 patients with a variety of cerebellopontine (CPA) tumors, at New York University School of Medicine. This included 146 unilateral acoustic neuromas, seven meningiomas, and six cases of neurofibromatosis. The suboccipital/retrosigmoid approach was used almost exclusively. The cochlear nerve was anatomically preserved in 131 cases, 32 percent of whom had successful hearing preservation. In the most successful group, hearing was preserved in 9 of 12 patients (75%). Success was defined as a postoperative pure-tone average (PTA) or speech reception threshold (SRT) of no more than 50 dB, and a speech discrimination score (SDS) of at least 50 percent. In those patients whose preoperative hearing was worse that this, success was based on a loss of no more than 10 dB in PTA or SRT, and 10 percent in SDS. Success was dependent mostly on extracanalicular (EC) tumor size, with the smallest tumors yielding the best results. When controlled for EC size, intracanalicular size and preoperative hearing were statistically significant variables. Origin from the superior vestibular nerve was also a favorable prognostic indicator. The character and duration of hearing loss, the patient's age, and the histology of the tumor did not have prognostic value. Auditory monitoring with either auditory brainstem response (ABR) or direct eighth nerve electrodes did not have a significant impact on success. Complications were somewhat increased by attempted hearing preservation. Facial nerve function was type I or II in 93 percent of patients. Cerebrospinal fluid leaks occurred in 15 percent of cases, but only 4 percent required surgical repair. There was one death, a patient with a 2.5-cm tumor. Early in the series, when a classic long vertical nuchal incision was used, headache and neck pain were common.

Adolescent↗
PubMed1991

Carboxypeptidase Y stability.

The stability of carboxypeptidase Y under different reaction conditions and in the presence various cosolvents was investigated. Loss of both hydrolysis and transpeptidation activities was monitored. Incubation of the enzyme at high temperatures or high pH resulted in the loss of both activities at the same rate. Addition of ammonium sulfate resulted in loss of transpeptidation activity but not hydrolysis activity. Addition of some organic solvents or Triton X-100 to the incubation mixture resulted in loss of both activities with transpeptidation being lost more rapidly than hydrolysis activity, while other organic solvents were observed to eliminate both activities entirely. Incubation of the enzyme in the presence of sodium dodecyl sulfate resulted in a decrease in both activities but hydrolysis was lost more rapidly than the transpeptidase activity. Implications of the observed preferential loss of activities to the labeling of peptides and proteins is discussed.

Ammonium Sulfate↗
PubMed1991

Structural requirements for nucleophilic substrates of carboxypeptidase Y.

The composition and structural aspects of the amino and carboxylic acid groups required for incorporation into peptides by transpeptidation and inhibition of hydrolysis in carboxypeptidase Y-catalyzed reactions were studied. Separation of these two groups by even one carbon prevents incorporation by transpeptidation and does not inhibit incorporation of other amino acids into model peptides. Substitution of phosphonic or sulfonic acids for the carboxylic acid group also results in loss of incorporation by transpeptidation. Only the sulfonic acid analog of glycine causes inhibition of hydrolysis and this inhibition is lost when serine is included in the reaction. d-Serine is not incorporated by carboxypeptidase Y, and its presence in the reaction mixture does not inhibit the incorporation of the L-isomer.

Carboxypeptidases↗
PubMed1991

Bilateral vocal cord teflon injection. An ineffective treatment for recurrent aspiration pneumonia.

Recurrent aspiration pneumonia is a potentially lethal problem, and its treatment is controversial. A variety of procedures have been advocated to prevent aspiration. These are reviewed briefly. We have been dissatisfied with established procedures because they usually require external approaches with considerable complexity and potential complications. Therefore, we attempted to obstruct the glottic airway by injecting both vocal cords with Teflon in a series of patients with recurrent aspiration pneumonia secondary to severe neurologic impairments. Since Teflon injection of the vocal cords bilaterally did not reliably prevent aspiration, we cannot recommend it for routine use in the treatment of chronic aspiration.

Humans↗
PubMed1991

Does intralaryngeal motor nerve sprouting occur following unilateral recurrent laryngeal nerve paralysis?

Reinnervation of paralyzed intralaryngeal muscles by axonal sprouting from adjacent intact muscles (the phenomenon of muscular neurotization) has been observed, but the source is uncertain. The potential for laryngeal reinnervation of the posterior cricoarytenoid muscle (PCA) from contralateral PCA motor nerve sprouting in a rabbit model was investigated. Unilateral PCA denervation was produced by vagotomy. The rabbits were examined for signs of PCA recovery for up to 6 months, using fiberoptic endoscopy, electromyography (EMG), and histology. No return of vocal cord abduction, EMG activity, or any nerve sprouting across the midline from the intact PCA was found. We conclude that there is no significant spontaneous intralaryngeal muscular neurotization to the paralyzed PCA. The clinical ramifications of our data will be discussed.

Animals↗
PubMed1990

Nucleotide sequence of Escherichia coli asnB and deduced amino acid sequence of asparagine synthetase B.

The Escherichia coli asparagine synthetase B gene (asnB) has been cloned into a temperature-sensitive, low copy plasmid, pOU71, as shown by the complementation of an E. coli asparagine auxotroph, E. coli JE6279. The nucleotide sequence of asnB and the flanking sequences were determined. The proposed coding region for the gene is 1662 nucleotides in length, and the deduced amino acid sequence of the coding region results in a protein that has a molecular weight of 62,666 and contains 554 amino acids. A promoter region is identified based on the transcription start site that was determined by primer extension experiments. Homology studies of the asnB protein sequence with the human asparagine synthetase and E. coli asparagine synthetase A protein show that there is a high degree of homology with only the human asparagine synthetase. A purF type glutamine amide transfer domain was identified upon inspection of the amino-terminal amino acid sequence of the asparagine synthetase B protein.

Amino Acid Sequence↗
PubMed1984

Asymmetric mass distribution of (Na+ + K+)-ATPase in membranes studied by freeze-fracture-etch electron microscopy.

SDS-purified porcine kidney (Na+ + K+)-ATPase was studied by thin-section and freeze-etch electron microscopy. Freeze-fracturing of resealed membrane fragments shows no difference in the distribution of intramembranous particles of approx. 9.0 nm in diameter between convex and concave fracture faces. However, two types of convex face are found: FA, which shows a rather smooth background with many intramembranous particles, and FB, which shows a textured background with very few or no intramembranous particles. Etching the fractured samples further reveals that FA faces are covered with many intramembranous particles, while the etched external faces (EA) are either irregularly granulated or reveal many particles half the size of intramembranous particles. FB faces are covered with distinct pits of 9 nm or larger. The etched external surfaces (EB) are covered with many particles of intramembranous particle size. These results suggest that there are two vesicle orientations in our resealed purified membrane preparation: right-side-out, as in vivo, and inside-out. The majority of the protein mass is distributed only on one side of the membranes. Right-side-out resealed membrane vesicles after fracturing and etching show particulated FA convex fracture faces and irregularly granulated or smooth etched EA surfaces, indicating that the FA face is the protoplasmic fracture face and that the majority of the protein mass of the (Na+ + K+)-ATPase is located on the cytoplasmic half of the membrane.

Animals↗
PubMedDate not supplied

Quantitation of immobilized proteins.

A method for the quantitative determination of immobilized proteins based on the binding and subsequent elution of Coomassie Blue R is presented. Also presented is a method for the immobilization of proteins in solution by entrapment in polyacrylamide. These entrapped proteins are then available for use in the assay method presented. Other analytical procedures can also be performed on the entrapped proteins, either alone or in combination with the protein quantitation. The dye binding and elution method presented provides a sensitive and, in most applications, rapid method for the quantitative detection of immobilized proteins. Rather than immobilization being an obstacle to the assay method, this approach utilizes the advantages of immobilization for the removal of excess reagents. Application of this approach to several types of immobilized protein are presented.

Acrylic Resins↗