Atomic-force-microscope-compatible near-field scanning microwave microscope with separated excitation and sensing probes

We present the design and experimental results of a near-field scanning microwave microscope working at a frequency of 1 GHz. Our microscope is unique in that the sensing probe is separated from the excitation electrode to significantly suppress the common-mode signal. Coplanar waveguides were patterned onto a silicon nitride cantilever interchangeable with atomic force microscope tips, which are robust for high speed scanning. In the contact mode that we are currently using, the numerical analysis shows that contrast comes from both the variation in local dielectric properties and the sample topography. Our microscope demonstrates the ability to achieve high resolution microwave images on buried structures, as well as nanoparticles, nanowires, and biological samples.

Wavelength-independent all-fiber mode converters

We have used two different photonic crystal fiber (PCF) techniques to make all-fiber mode converters. An LP(01) to LP(11) mode converter was made by the ferrule technique on a drawing tower, and an LP(01) to LP(02) mode converter was made by controlled hole inflation of an existing PCF on a tapering rig. Both devices rely on adiabatic propagation rather than resonant coupling; so high extinction was achieved across a wide wavelength range.

All-fiber anamorphic core-shape transitions

We demonstrate low-loss anamorphic transitions between circular and rectangular fiber cores with aspect ratios up to 5:1, and hence improved coupling from a diode laser by using only a spherical lens. Differential hole pressurization and localized heating of a stock photonic crystal fiber inflates the holes at different rates. Some holes are plugged in the fiber end face where pressure is applied, so they remain at ambient pressure. Alternatively, holes of different sizes expand at different rates because the effective pressure due to surface tension differs.

Intervalley gap anomaly of two-dimensional electrons in silicon

We report here a systematic study of the energy gaps at the odd-integer quantum Hall states nu = 3 and 5 under tilted magnetic (B) fields in a high quality Si two-dimensional electron system. Out of the coincidence region, the valley splitting is independent of the in-plane fields. However, the nu = 3 valley gap differs by about a factor of 3 (Deltav approximately 0.4 vs 1.2 K) on different sides of the coincidence. More surprisingly, instead of reducing to zero, the energy gaps at nu = 3 and 5 rise rapidly when approaching the coincidence angles. We believe that such an anomaly is related to strong couplings of the nearly degenerate Landau levels.

Two-flux composite fermion series of the fractional quantum Hall states in strained Si

Magnetotransport properties are investigated in a high-mobility two-dimensional electron system in the strained Si quantum well of a (100) Si(0.75)Ge(0.25)/Si/Si(0.75)Ge0.25 heterostructure, at temperatures down to 30 mK and in magnetic fields up to 45 T. We observe around nu=1/2 the two-flux composite fermion (CF) series of the fractional quantum Hall effect (FQHE) at nu=2/3, 3/5, 4/7, and at nu=4/9, 2/5, 1/3. Among these FQHE states, the nu=1/3, 4/7, and 4/9 states are seen for the first time in the Si/SiGe system. Interestingly, of the CF series, the 3/5 state is weaker than the nearby 4/7 state and the 3/7 state is conspicuously missing, resembling the observation in the IQHE regime that the nu=3 is weaker than the nearby nu=4 state. Our results can be quantitatively understood in the picture of CF's with the valley degree of freedom.

Human uveal melanoma expresses NG2 immunoreactivity

BACKGROUND/AIMS

NG2 is the rat homologue of the human melanoma proteoglycan (HMP), also known as the high molecular weight melanoma associated antigen. Most cutaneous melanomas, as well as glioblastomas, chondrosarcomas, and some leukaemias express NG2 immunoreactivity, recognised using monoclonal antibody (mAb) 9.2.27. This antibody has also been used for molecular targeting in targeted alpha therapy for melanoma. The purpose of this study was to evaluate the expression of NG2 immunoreactivity in human uveal melanoma and normal ocular tissue using mAb 9.2.27.

METHODS

Enucleated eyes from 26 patients with choroidal or ciliary body melanoma (n=26) were available as paraffin sections, and stained with haematoxylin and eosin to assess for tumour cell type and histopathology. Additional slides were investigated for NG2 immunoreactivity using mAb 9.2.27 and alkaline phosphatase anti-alkaline phosphatase (APAAP) immunostaining. Two independent observers graded immunostaining using a semiquantitative scale from 0 (negative) to 3 (strong).

RESULTS

Immunostaining for mAb 9.2.27 could not be graded in 7/26 cases with dense pigmentation of the tumour. For the remaining cases, grade 2 (moderate) or more immunostaining was seen in 18/19 tumours (95%). The retina, retinal pigment epithelium (RPE), and choroid displayed weak immunostaining (grade 0.5-1.5) in the majority of melanoma affected eyes. Normal retina and choroid (n=5) appeared negative for mAb 9.2.27. Optic nerve axon bundles in both control and melanoma affected eyes displayed moderate immunostaining.

CONCLUSION

In the present study, the majority of human uveal melanomas expressed NG2 immunoreactivity, as detected using mAb 9.2.27. This antibody may be a suitable candidate for radioimmunotherapy to target ocular melanoma.

GALT deficiency causes UDP-hexose deficit in human galactosemic cells

Previously we reported that stable transfection of human UDP-glucose pyrophosphorylase (hUGP2) rescued galactose-1-phosphate uridyltransferase (GALT)-deficient yeast from "galactose toxicity." Here we test in human cell lines the hypothesis that galactose toxicity was caused by excess accumulation of galactose-1-phosphate (Gal-1-P), inhibition of hUGP2, and UDP-hexose deficiency. We found that SV40-transformed fibroblasts derived from a galactosemic patient accumulated Gal-1-P from 1.2+/-0.4 to 5.2+/-0.5 mM and stopped growing when transferred from 0.1% glucose to 0.1% galactose. Control fibroblasts accumulated little Gal-1-P and continued to grow. The GALT-deficient cells had 157+/-10 micromoles UDP-glucose/100 g protein and 25+/-5 micromoles UDP-galactose/100 g protein when grown in 0.1% glucose. The control cells had 236+/-25 micromoles UDP- glucose/100 g protein and 82+/-10 micromoles UDP-galactose/100 g protein when grown in identical medium. When we transfected the GALT-deficient cells with either the hUGP2 or GALT gene, their UDP-glucose content increased to 305+/-28 micromoles/100 g protein (hUGP2-transfected) and 210+/-13 micromoles/100 g protein (GALT-transfected), respectively. Similarly, UDP-galactose content increased to 75+/-12 micromoles/100 g protein (hUGP2-transfected) and 55+/-9 micromoles/100 g protein (GALT-transfected), respectively. Though the GALT-transfected cells grew in 0.1% galactose with little accumulation of Gal-1-P (0.2+/-0.02 mM), the hUGP2-transfected cells grew but accumulated some Gal-1-P (3.1+/-0.4 mM). We found that 2.5 mM Gal-1-P increased the apparent KM of purified hUGP2 for glucose-1-phosphate from 19.7 microM to 169 microM, without changes in apparent Vmax. The Ki of the reaction was 0.47 mM. Gal-1-P also inhibited UDP-N-acetylglucosamine pyrophosphorylase, which catalyzes the formation of UDP-N-acetylglucosamine. We conclude that intracellular concentrations of Gal-1-P found in classic galactosemia inhibit UDP-hexose pyrophosphorylases and reduce the intracellular concentrations of UDP-hexoses. Reduced Sambucus nigra agglutinin binding to glycoproteins isolated from cells with increased Gal-1-P is consistent with the resultant inhibition of glycoprotein glycosylation.

Reciprocal antagonism between estrogen receptor and NF-kappaB activity in vivo

The functional interaction, or "cross-talk," between estrogen receptor (ER) and the proinflammatory transcription factor nuclear factor (NF)-kappaB demonstrated in vitro has been suggested to play a role in estrogen prevention of cardiovascular disease. Here, we demonstrate that this reciprocal cross-talk occurs in vivo. Ovariectomized C57BL/6 mice fed an atherogenic diet had increased hepatic levels of active NF-kappaB and numerous inflammatory genes, including MHC invariant chain (Ii), vascular cell adhesion molecule-1, tumor necrosis factor-alpha, and RANTES. Treatment with 17alpha-ethinylestradiol (EE) strongly blocked induction of these genes but had no effect on their basal expression levels. ER was required for this activity, because the antagonist ICI 182,780 completely blocked the inhibitory activity of EE. Gene activation by EE was not required for inhibition of inflammatory gene expression, because both the phytoestrogen genistein and low doses of EE were effective in blocking inflammatory gene induction without inducing marker genes such as intestinal trefoil factor (ITF) or myo-inositol-1-phosphate synthase (IPS). The in vivo transcriptional interference was reciprocal, with EE induction of ITF and IPS greatly reduced in animals fed the atherogenic diet versus chow-fed controls. This interference was specific to the liver, because diet had no effect on uterine weight increases produced by EE. Transfection experiments confirmed that the extent of inhibition of ER-mediated transcription by inflammatory stimuli correlated with the extent of NF-kappaB activation. These results suggest that the cross-talk between ER and NF-kappaB does occur in vivo and may indeed contribute significantly to the cardioprotective effects of estrogen.

Preservation of light signaling to the suprachiasmatic nucleus in vitamin A-deficient mice

To investigate the role of retinal-based pigments (opsins) in circadian photoreception in mice, animals mutated in plasma retinol binding protein were placed on a vitamin A-free diet and tested for photic induction of gene expression in the suprachiasmatic nucleus. After 10 months on the vitamin A-free diet, the majority of mice contained no detectable retinal in their eyes. These mice demonstrated fully intact photic signaling to the suprachiasmatic nucleus as measured by acute mPer mRNA induction in the suprachiasmatic nucleus in response to bright or dim light. The data suggest that a non-opsin pigment is the primary circadian photoreceptor in the mouse.

Structure-function analyses of a common mutation in blacks with transferase-deficiency galactosemia

We previously identified a missense mutation at amino acid 135 of human galactose 1-phosphate uridyltransferase (hGALT) in which a leucine (TTG) was substituted for a serine (TCG), S135L. This mutation was common in black patients with galactosemia and homozygotes (S135L/S135L) had no GALT activity or protein in their erythrocytes or lymphoblasts. However, there was residual GALT activity and protein in their leukocytes, and they had near normal total body [13C]galactose oxidation to 13CO2 in breath. To evaluate the biochemical mechanism(s) producing these effects, we overexpressed hGALT proteins with site-directed mutations in this nonconserved amino acid in a GALT-minus Escherichia coli. Enzyme activities detected in bacterial lysates overexpressing either S135 (wild type), A135, C135, H135, L135, S132-H135, T135, or Y135 were 100, 4.7, 3.0, 4.0, 2.7, 0.7, 35.4, and 1.4%, respectively. Only the threonine substitution (S135T) had significant enzyme activity in these lysates. There was also decreased abundance of all mutant proteins in the lysates exposed to bacterial proteolysis during preparation and analysis. This added the variable of bio-instability to analysis of enzyme activities in lysates. To further characterize the catalytic role of serine at amino acid 135 and to differentiate bio-instability from impaired catalysis by the leucine substitution, we purified wild-type and L135-hGALT proteins to homogeneity and analyzed identical amounts of enzyme protein. We found that the apparent Vmax of the purified L135-hGALT protein was significantly reduced from 80 +/- 5.9 to 5.8 +/- 1.8 micromol glucose 1-phosphate released/min/mg hGALT protein with no increase in KM for galactose 1-phosphate for the second displacement. The first displacement reaction, although three orders of magnitude slower, was similar between the wild type and L135-hGALT. We conclude that a hydroxyl group on amino acid 135 is required for the catalysis of uridyl transfer from UDP-glucose to UDP-galactose in the presence of galactose 1-phosphate, and plays a role in the bio-stability of hGALT.

Expression and characterization of a murine enzyme able to cleave beta-carotene. The formation of retinoids

Because animals are not able to synthesize retinoids de novo, ultimately they must derive them from dietary provitamin A carotenoids through a process known as carotene cleavage. The enzyme responsible for catalyzing carotene cleavage (beta-carotene 15,15'-dioxygenase) has been characterized primarily in rat intestinal scrapings. Using a recently reported cDNA sequence for a carotene cleavage enzyme from Drosophila, we identified a cDNA encoding a mouse homolog of this enzyme. When the cDNA was expressed in either Escherichia coli or Chinese hamster ovary cells, expression conferred upon bacterial and Chinese hamster ovary cell homogenates the ability to cleave beta-carotene to retinal. Several lines of evidence obtained upon kinetic analyses of the recombinant enzyme suggested that carotene cleavage enzyme interacts with other proteins present within cell or tissue homogenates. This was confirmed by pull-down experiments upon incubation of recombinant enzyme with tissue 12,000 x g supernatants. Matrix-assisted laser desorption ionization-mass spectrometry analysis of pulled-down proteins indicates that an atypical testis-specific isoform of lactate dehydrogenase associates with recombinant carotene cleavage enzyme. mRNA transcripts for the carotene cleavage enzyme were detected by reverse transcription-polymerase chain reaction in mouse testes, liver, kidney, and intestine. In situ hybridization studies demonstrated that carotene cleavage enzyme is expressed prominently in maternal tissue surrounding the embryo but not in embryonic tissues at 7.5 and 8.5 days postcoitus. This work offers new insights for understanding the biochemistry of carotene cleavage to retinoids.

Functional analysis of the human galactose-1-phosphate uridyltransferase promoter in Duarte and LA variant galactosemia

Human galactose-1-phosphate uridyltransferase (hGALT) is an evolutionarily conserved enzyme central to D-galactose metabolism. The impairment of hGALT causes galactosemia. One missense mutation, an aspartate to asparagine substitution at amino acid 314 (N314D), impairs 50% activity in the homozygous state in some patients but gives near normal activity in others. The former condition is called Duarte (D) and the latter, Los Angeles (LA). The D allele is linked to hGALT polymorphisms including a deletion 5'to the translation start site (-119 to -116delGTCA), g1391G --> A and g1105G --> C. The LA allele is linked to a g1721C --> T transition. To investigate possible mechanisms for differences in hGALT activity between the D and LA alleles, we sequenced 3951 nucleotides of genomic DNA 5' to the hGALT translation start site. Using a dual-luciferase reporter system to express deletion constructs of the hGALT promoter, we noted both positive and negative regulatory regions. Two putative positive regulatory domains overlap with the naturally occurring -119 to -116delGTCA linked to Duarte. One is an E-box motif (CACGTG) at -117 to -112 bp. The second is an AP-1 motif (TCAGTCAG) at -124 to -119 bp. The delGTCA mutation confers reduced luciferase activity to transfected cell lines derived from human ovarian and liver neoplasms. Additionally, human lymphoblasts derived from patients with the Duarte allele have reduced GALT mRNA. We conclude that the human GALT gene is regulated in the first -165 bp of its promoter region by positive regulators of GALT gene expression. The -119 to -116delGTCA reduces hGALT transcription resulting in reduced GALT activity in the Duarte allele.

[The engulfment effects of macrophage on apoptotic eosinophils treated by anti-Fas monoclonal antibody in vitro]

OBJECTIVE

Expression of the Fas antigen and induction of apoptosis in eosinophils (EOS) by anti-Fas antibody in vitro were investigated.

METHODS

The purified EOS from healthy donors were cultured for 72 h in the presence of human IL-5 and with or without anti-Fas monoclonal antibody (MPhiAb) at various concentrations (1 approximately 1 000 ng/ml). The changes of eosinophil viability, percentage of apoptosis, and fragmented DNA electrophoresis were observed. The eosinophils treated by Fas MPhiAb for 24 h, 48 h, 72 h were cultured with monocyte-derived macrophages, the positive percentage of macrophages which engulfed EOS was calculated.

RESULTS

The anti-Fas MoAb suppressed IL-5-mediated EOS survival in dose- and time-dependant manner. High concentration of IL-5 (10(6)U/L) could not inhibit anti-Fas MoAb-mediated apoptosis. The percentage of apoptosis was (35 +/- 6)% after 24 h treated with Fas MoAb (P < 0.01), and increased to (96 +/- 3)% after 72 h (P < 0.01). The percentage of macrophages which engulfed eosinophils was significantly higher than control (P < 0.01).

CONCLUSION

The anti-Fas MoAb can efficiently induced eosinophils apoptosis, apoptotic EOS induced by anti-Fas MoAb could be engulfed by macrophages.

Enhancement of seed oil content by expression of glycerol-3-phosphate acyltransferase genes

Arabidopsis thaliana was transformed with a plastidial safflower glycerol-3-phosphate acyltransferase (GPAT) and an Escherichia coli GPAT. The genes were used directly and in modified forms with, as applicable, the plastidial targeting sequence removed, and with an endoplasmic reticulum targeting sequence added. Seeds of plants transformed using only the vector were indistinguishable in oil content from wild-type control plants. All other gene constructs increased seed oil content. The unmodified safflower gene (spgpat) produced oil increases ranging from 10 to 21%. On average, the greatest increase (+22%) was observed in seeds of transformants carrying the spgpat with the targeting peptide removed. The E. coli plsB gene increased seed oil content by an average of 15%.

Chitin synthase in the filarial parasite, Brugia malayi

Fragments of putative chitin synthase (chs) genes from two filarial species (Brugia malayi and Dirofilaria immitis) were amplified by PCR using degenerate primers. The full genomic and cDNA sequences were obtained for the B. malayi chs gene (Bm-chs-1); the predicted amino acid sequence is highly similar, over a large region, to two CHS sequences of the nematode Caenorhabditis elegans and also to two insect CHS sequences. Bm-chs-1 is abundantly transcribed in B. malayi adult females, independent of their fertilization status, but is also expressed in males and microfilariae. Oocytes and early embryos contain large amounts of Bm-chs-1 transcript by in situ hybridization, but later stage embryos within the maternal uterus show little or no Bm-chs-1 transcript. No specific hybridization could be demonstrated in maternal somatic tissues. Polyclonal antibodies were raised against a peptide expressed from a recombinant cDNA fragment of Bm-chs-1; immunostaining detected CHS protein in oocytes and early to midstage embryos. These studies characterize a gene that is likely to be essential to oogenesis and embryonic development in a parasitic nematode. Because chitin synthesis and eggshell formation begin after fertilization, the presence of CHS protein in early oocytes suggests that the enzyme must be activated as a result of fertilization. These studies also demonstrate that chitin synthesis may not be restricted to eggshell formation in nematodes, as the Bm-chs-1 gene is transcribed in life cycle stages other than adult females.

Duarte allele impairs biostability of galactose-1-phosphate uridyltransferase in human lymphoblasts

The Duarte allele (D) is a missense mutation (N314D) that produces a characteristic isoform and partial impairment of galactose-1-phosphate uridyltransferase (GALT) in human erythrocytes, fibroblasts, and transformed lymphoblasts. The position of this amino acid is distant, however, from presumptive catalytic site(s) as deduced from a three-dimensional model of crystallized Escherichia coli galT protein. To evaluate the mechanism(s) involved in the partial impairment of enzymatic activity, we compared the activity, abundance, biological stability, and mRNA of GALT in human lymphoblastoid cell lines cultured from individuals homozygous for wild-type (WT/WT) and Duarte alleles (N314D/N314D). No other nucleotide differences were present in their GALT genes. The apparent Vmax was reduced in N314D/N314D cells to 31 +/- 3.6 compared to WT/WT of 54 +/- 6.5 nmole UDP-galactose formed/g cell protein/hour. Both genotypes had similar apparent KMs for UDP-glucose of 0.142 +/- 0.057 mM and 0.133 +/- 0.056 mM. This reduced Vmax was associated with a reduced abundance of the 86kD GALT dimer as determined by Western blots and densitometry. Using RNase protection assays, this reduced GALT protein in the N314D/N314D cell lines was not associated with reduced abundance of GALT mRNA. Using cycloheximide (3-[2-(3,5-Dimethyl-2-oxocyclohexyl)-2-hydroxyethyl]glutarimide) inhibition of de novo protein synthesis, GALT enzyme activity, and its dimeric protein had a biological T1/2 of approximately 24 hours in N314D/N314D cell lines as compared to 50 hours for WT/WT lymphoblasts. Upon exposure to 50 degrees C for 15 minutes, N314D/ N314D lymphoblasts retained 45% of GALT activity, whereas controls retained 77% activity. Reduced activity and thermal sensitivity caused by the N314D mutation reverted to control values when a lysine was substituted for a glutamic acid at amino acid 203 in cis (E203K). In summary, N314D/N314D lymphoblasts have reduced GALT enzyme capacity, dimeric protein abundance, biological, and thermal stability. We conclude that the substitution of aspartate for asparagine at amino acid 314 in the human GALT protein reduces the biostability of the active enzyme in human lymphoblasts.

Overexpression of human UDP-glucose pyrophosphorylase rescues galactose-1-phosphate uridyltransferase-deficient yeast

To better understand the pathophysiology of galactose-1-phosphate uridyltransferase (GALT) deficiency in humans, we studied the mechanisms by which a GALT-deficient yeast survived on galactose medium. Under normal conditions, GALT-deficient yeast cannot grow in medium that contains 0.2% galactose as the sole carbohydrate, a phenotype of Gal(-). We isolated revertants from a GALT-deficient yeast by direct selection for growth in galactose, a phenotype of Gal(+). Comparison of gene expression profiles among wild-type and revertant strains on galactose medium revealed that the revertant down-regulated genes encoding enzymes including galactokinase, galactose permease, and UDP-galactose-4-epimerase (the GAL regulon). By contrast, the revertant strain up-regulated the gene for UDP-glucose pyrophosphorylase, UGP1. There was reduced accumulation of galactose-1-phosphate in the galactose-grown revertant cells when compared to the GALT-deficient parent cells. In vitro biochemical analysis showed that UDP-glucose pyrophosphorylase had bifunctional properties and could catalyze the conversion of galactose-1-phosphate to UDP-galactose in the presence of UTP. To test if augmented expression of this gene could produce a Gal(+) phenotype in the GALT-deficient parent cells, we overexpressed the yeast UGP1 and the human homolog, hUGP2 in the mutant strain. The Gal(-) yeast transformed with either UGP1 or hUGP2 regained their ability to grow on galactose. We conclude that revertant can grow on galactose medium by reducing the accumulation of toxic precursors through down-regulation of the GAL regulon and up-regulation of the UGP1 gene. We speculate that increased expression of hUGP2 in humans could alleviate poor outcomes in humans with classic galactosemia.

Chromosomal differentiation of the Schistosoma japonicum complex

The C-banding pattern, location of telomere sequence and chiasma frequency of four species of the Schistosoma japonicum complex were compared with those of two African species, Schistosoma mansoni and Schistosoma haematobium. In the six species, C-banding patterns of seven autosomes and the two sex chromosomes (Z and W) showed relatively species-specific and geographical (Asian and African) differences. Particularly, a plausible pathway of alteration of chromosome 2 revealed a direction from the A-chromosome to the M- chromosome in terms of rearrangements of pericentric inversion and elimination of constitutive heterochromatin (AM inversion). This chromosome change suggested hypothetically that the S. japonicum complex is the original type, and the African species represents the derived type. Moreover, the mosaic construct of the Asian and African types in Schistosoma sinensium chromosomes prompted us to propose that the species might have been formed by hybrid speciation of the genomes of Asian and African species. Localisation of telomeric repeats enabled Asian and African schistosomes to be distinguished clearly by simple terminal location and by terminal and interstitial locations, respectively. Change of chiasma frequency in the S. japonicum complex might be caused by the reduction of interstitial chiasmate (Xi) in the larger chromosomes, 1 and Z (or W), and the change seems to have progressed to Japan from South East Asia. These data enabled us to predict a tentative evolutionary pathway of schistosomes at the cytogenetic level.

An evaluation of whole blood testing for Helicobacter pylori infection in the Chinese population

BACKGROUND

Near patient tests for Helicobacter pylori were developed to assist in the management of dyspepsia patients in general practice. Most studies were performed in western populations.

AIM

To evaluate the rapid whole blood test (Flexpack HP) for H. pylori in the Chinese population.

METHODS

Consecutive dyspeptic patients referred for upper endoscopy were recruited. During upper endoscopy, biopsies were taken from the antrum and corpus for rapid urease test (CLO test) and histological examination. After endoscopy, the whole blood test (FlexPack HP) was performed according to the manufacturer's instruction. Patients then received a 13C-urea breath test. Results of the whole blood test were compared with the gold standard (CLO test, histology and 13C-urea breath test).

RESULTS

A total of 294 consecutive patients gave a valid Flexpack HP result for interpretation. The mean age of patients was 47.7 (range 15-85) years. Analysis showed a sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 58%, 92%, 91%, 63% and 73% respectively.

CONCLUSION

The FlexPack HP whole blood test showed good specificity but lacked sensitivity. It is not sensitive enough to be used in a general practice setting for the test-and-treat approach in the Chinese population.

Rational design of organophosphorus hydrolase for altered substrate specificities

Organophosphorus hydrolase (OPH) is a bacterial enzyme that hydrolyzes a broad variety of OP neurotoxins, including chemical warfare agents and many widely used pesticides. OPH has extremely high hydrolytic efficiency with different phosphotriester and phophothiolester pesticides (k(cat) = 50-15,000 s(-1)) as well as phosphorofluorates such as DFP and the chemical warfare agents sarin and soman (k(cat) = 50-11,000 s(-1)). In contrast, the enzyme has much lower catalytic capabilities for phosphonothioate neurotoxins such as acephate or the chemical warfare agent VX [O-ethyl S-(2-diisopropyl aminoethyl) methylphosphonothioate] (k(cat) = 0.3-20 s(-1)). Different metal-associated forms of the enzyme have demonstrated varying hydrolytic capabilities for each of the OP neurotoxins, and the activity of OPH (Co2+) is consistently higher than that of OPH (Zn2+) by five- to 20-fold. Protein engineering strategies have exploited these metal-induced catalytic differences, and other slight modifications to the opd gene have resulted in significant enhancement of the rates of detoxification of the thioate pesticides and chemical warfare agents. In order to develop practical applications of OPH, other experiments have focused on improvement of enzyme production, localization, stability, and shelf-life, as well as efficient catalysis of substrates of interest.

Wedge factor dependence with depth, field size, and nominal distance--a general computational rule

We have investigated the dependence of the wedge factors with field size, depth, nominal, and extended distances for 4, 6, 18, and 24 MV photon beams. Analysis of the experimental data suggests a general linear dependence of the wedge factors with field size and depth. The study shows that changes in wedge factors are insignificant (< or = +/-1.0%) with respect to measurements at nominal SSD, SAD, or extended SSD. This independence of the wedge factors on source-to-surface distance was studied for different photon energies (4-24 MV) and for different attenuating wedges (external and internal wedges). For clinical applications, an algorithm is presented to calculate the wedge factor dependence with field size and depth. The new algorithm has been successfully implemented to replace wedge look-up tables for dose and MU calculations in PRISM 1.2 treatment planning system used in our department.

Modification of near active site residues in organophosphorus hydrolase reduces metal stoichiometry and alters substrate specificity

Organophosphorus hydrolase (OPH, EC 8.1.3.1) is a dimeric, bacterial enzyme that detoxifies many organophosphorus neurotoxins by hydrolyzing a variety of phosphonate bonds. The histidinyl residues at amino acid positions 254 and 257 are located near the bimetallic active site present in each monomer. It has been proposed that these residues influence catalysis by interacting with active site residues and the substrate in the binding pocket. We replaced the histidine at position 254 with arginine (H254R) and the one at position 257 with leucine (H257L) independently to form the single-site-modified enzymes. The double modification was also constructed to incorporate both changes (H254R/H257L). Although native OPH has two metals at each active site (four per dimer), all three of these altered enzymes possessed only two metals per dimer while retaining considerable enzymatic activity for the preferred phosphotriester (P-O bond) substrate, paraoxon (5-100% kcat). The three altered enzymes achieved a 2-30-fold increase in substrate specificity (kcat/Km) for demeton S (P-S bond), an analogue for the chemical warfare agent VX. In contrast, the substrate specificity for diisopropyl fluorophosphonate (P-F bond) was substantially decreased for each of these enzymes. In addition, H257L and H254R/H257L showed an 11- and 18-fold increase, respectively, in specificity for NPPMP, the analogue for the chemical warfare agent soman. These results demonstrate the ability to significantly enhance the specificity of OPH for various substrates by site-specific modifications, and it is suggested that changes in metal requirements may affect these improved catalytic characteristics by enhancing structural flexibility and improving access of larger substrates to the active site, while simultaneously decreasing the catalytic efficiency for smaller substrates.

The biochemical role of glutamine 188 in human galactose-1-phosphate uridyltransferase

The substitution of arginine for glutamine at amino acid 188 (Q188R) ablates the function of human galactose-1-phosphate uridyltransferase (GALT) and is the most common mutation causing galactosemia in the white population. GALT catalyzes two consecutive reactions. The first reaction binds UDP-glucose (UDP-Glu), displaces glucose-1-phosphate (glu-1-P), and forms the UMP-GALT intermediate. In the second reaction, galactose-1-phosphate (gal-1-P) is bound, UDP-galactose (UDP-Gal) is released, and the free enzyme is recycled. In this study, we modeled glutamine, asparagine, and a common mutation arginine at amino acid 188 on the three-dimensional model of the Escherichia coli GALT-UMP protein crystal. We found that the amide group of the glutamine side chain could provide two hydrogen bonds to the phosphoryl oxygens of UMP with lengths of 2.52 and 2.82 A. Arginine and asparagine could provide only one hydrogen bond of 2. 52 and 3.02 A, respectively. To test this model, we purified recombinant human Gln188-, Arg188-, and Asn188-GALT and analyzed the first reaction in the absence of gal-1-P by quantitating glu-1-P released using enzyme-linked methods. Gln188-GALT displaced 80 +/- 7. 0 nmol glu-1-P/mg GALT/min in the first reaction. By contrast, both Arg188- and Asn188-GALT released more glu-1-P (170 +/- 8.0 and 129 +/- 28.4 nmol/mg GALT/min, respectively). The overall, double displacement reaction was quantitated in the presence of gal-1-P. Gln188-GALT produced 80,030 +/- 5,910 nmol glu-1-P/mg GALT/min, whereas the mutant Arg188- and Asn188-GALT released only 600 +/- 71. 2 and 2960 +/- 283.6 nmole glu-1-P/mg GALT/min, respectively. We conclude from these data that glutamine at position 188 stabilizes the UMP-GALT intermediate through hydrogen bonding and enables the double displacement of both glu-1-P and UDP-Gal. The substitution of arginine or asparagine at position 188 reduces hydrogen bonding and destabilizes UMP-GALT. The unstable UMP-GALT allows single displacement of glu-1-P with release of free GALT but impairs the subsequent binding of gal-1-P and displacement of UDP-Gal.