[Interaction between the metal ion in the active site of cytochrome C and copper sulfate by ultraviolet spectroscopy]

The direct interaction between the metal ion in the active center of cytochrome C (Fecyt-C) and inorganic copper sulfate in pH 7.1 phosphate has been studied by UV spectrometry. As a result, part of the metal ion Fe(II) in Fecyt-C was replaced by Cu(II) and the corresponding cytochrome C derivatives Cucyt-C were produced, in addition, the interaction was increased with amount of copper sulfate added. The direct interaction between the CuSO4 and metal ion of cytochrome C was verified for the first time.

Mechanistic studies on class I polyhydroxybutyrate (PHB) synthase from Ralstonia eutropha: class I and III synthases share a similar catalytic mechanism

The Class I and III polyhydroxybutyrate (PHB) synthases from Ralstonia eutropha and Chromatium vinosum, respectively, catalyze the polymerization of beta-hydroxybutyryl-coenzyme A (HBCoA) to generate PHB. These synthases have different molecular weights, subunit composition, and kinetic properties. Recent studies with the C. vinosum synthase suggested that it is structurally homologous to bacterial lipases and allowed identification of active site residues important for catalysis [Jia, Y., Kappock, T. J., Frick, T., Sinskey, A. J., and Stubbe, J. (2000) Biochemistry 39, 3927-3936]. Sequence alignments between the Class I and III synthases revealed similar residues in the R. eutropha synthase. Site-directed mutants of these residues were prepared and examined using HBCoA and a terminally saturated trimer of HBCoA (sT-CoA) as probes. These studies reveal that the R. eutropha synthase possesses an essential catalytic dyad (C319-H508) in which the C319 is involved in covalent catalysis. A conserved Asp, D480, was shown not to be required for acylation of C319 by sT-CoA and is proposed to function as a general base catalyst to activate the hydroxyl of HBCoA for ester formation. Studies of the [(3)H]sT-CoA with wild-type and mutant synthases reveal that 0.5 equiv of radiolabel is covalently bound per monomer of synthase, suggesting that a dimeric form of the enzyme is involved in elongation. These studies, in conjunction with search algorithms for secondary structure, suggest that the Class I and III synthases are mechanistically similar and structurally homologous, despite their physical and kinetic differences.

Crystal structure of the complex of concanavalin A and tripeptide

The X-ray structure analysis of a cross-linked crystal of concanavalin A soaked with the tripeptide molecule as the probe molecule showed electron density corresponding to full occupation in the binding pocket. The site lies on the surface of concanavalin A and is surrounded by three symmetry-related molecules. The crystal structure of the tripeptide complex was refined at 2.4-A resolution to an R-factor of 17.5%, (Rfree factor of 23.7%), with an RMS deviation in bond distances of 0.01 A. The model includes all 237 residue of concanavalin A, 1 manganese ion, 1 calcium ion, 161 water molecules, 1 glutaraldehyde molecule, and 1 tripeptide molecule. This X-ray structure analysis also provides an approach to mapping the binding surface of crystalline protein with a probe molecule that is dissolved in a mixture of organic solvent with water or in neat organic solvent but is hardly dissolved in aqueous solution.

[Clinical study of preoperative orthodontic treatment for patients with cleft lip and palate]

OBJECTIVE

To discuss the indication and time of preoperative orthodontic treatment for the patients with cleft lip and palate.

METHODS

16 cleft lip and palate patients (BCLP 6, UCLP 10) with severe cross-bite were selected. Edgewise appliance was used for the alignment and upper arch was expanded with quadhelix.

RESULTS

After the orthodontic treatment, upper and lower arches were well aligned and the arch form was normal. Decompensation was achieved. Model surgery revealed that the upper and lower arches were harmonious.

CONCLUSION

Preoperative orthodontic treatment is the key point to ensure the success of the surgery and to prevent relapse. Orthodontic/surgical approach can improve the patients' profile and function.

Dynamics and folding of single two-stranded coiled-coil peptides studied by fluorescent energy transfer confocal microscopy

We report single-molecule measurements on the folding and unfolding conformational equilibrium distributions and dynamics of a disulfide crosslinked version of the two-stranded coiled coil from GCN4. The peptide has a fluorescent donor and acceptor at the N termini of its two chains and a Cys disulfide near its C terminus. Thus, folding brings the two N termini of the two chains close together, resulting in an enhancement of fluorescent resonant energy transfer. End-to-end distance distributions have thus been characterized under conditions where the peptide is nearly fully folded (0 M urea), unfolded (7.4 M urea), and in dynamic exchange between folded and unfolded states (3.0 M urea). The distributions have been compared for the peptide freely diffusing in solution and deposited onto aminopropyl silanized glass. As the urea concentration is increased, the mean end-to-end distance shifts to longer distances both in free solution and on the modified surface. The widths of these distributions indicate that the molecules are undergoing millisecond conformational fluctuations. Under all three conditions, these fluctuations gave nonexponential correlations on 1- to 100-ms time scale. A component of the correlation decay that was sensitive to the concentration of urea corresponded to that measured by bulk relaxation kinetics. The trajectories provided effective intramolecular diffusion coefficients as a function of the end-to-end distances for the folded and unfolded states. Single-molecule folding studies provide information concerning the distributions of conformational states in the folded, unfolded, and dynamically interconverting states.

tA single amino acid difference distinguishes resistant and susceptible alleles of the rice blast resistance gene Pi-ta

The rice blast resistance (R) gene Pi-ta mediates gene-for-gene resistance against strains of the fungus Magnaporthe grisea that express avirulent alleles of AVR-Pita. Using a map-based cloning strategy, we cloned Pi-ta, which is linked to the centromere of chromosome 12. Pi-ta encodes a predicted 928-amino acid cytoplasmic receptor with a centrally localized nucleotide binding site. A single-copy gene, Pi-ta shows low constitutive expression in both resistant and susceptible rice. Susceptible rice varieties contain pi-ta(-) alleles encoding predicted proteins that share a single amino acid difference relative to the Pi-ta resistance protein: serine instead of alanine at position 918. Transient expression in rice cells of a Pi-ta(+) R gene together with AVR-Pita(+) induces a resistance response. No resistance response is induced in transient assays that use a naturally occurring pi-ta(-) allele differing only by the serine at position 918. Rice varieties reported to have the linked Pi-ta(2) gene contain Pi-ta plus at least one other R gene, potentially explaining the broadened resistance spectrum of Pi-ta(2) relative to Pi-ta. Molecular cloning of the AVR-Pita and Pi-ta genes will aid in deployment of R genes for effective genetic control of rice blast disease.

tA single amino acid difference distinguishes resistant and susceptible alleles of the rice blast resistance gene Pi-ta

The rice blast resistance (R) gene Pi-ta mediates gene-for-gene resistance against strains of the fungus Magnaporthe grisea that express avirulent alleles of AVR-Pita. Using a map-based cloning strategy, we cloned Pi-ta, which is linked to the centromere of chromosome 12. Pi-ta encodes a predicted 928-amino acid cytoplasmic receptor with a centrally localized nucleotide binding site. A single-copy gene, Pi-ta shows low constitutive expression in both resistant and susceptible rice. Susceptible rice varieties contain pi-ta(-) alleles encoding predicted proteins that share a single amino acid difference relative to the Pi-ta resistance protein: serine instead of alanine at position 918. Transient expression in rice cells of a Pi-ta(+) R gene together with AVR-Pita(+) induces a resistance response. No resistance response is induced in transient assays that use a naturally occurring pi-ta(-) allele differing only by the serine at position 918. Rice varieties reported to have the linked Pi-ta(2) gene contain Pi-ta plus at least one other R gene, potentially explaining the broadened resistance spectrum of Pi-ta(2) relative to Pi-ta. Molecular cloning of the AVR-Pita and Pi-ta genes will aid in deployment of R genes for effective genetic control of rice blast disease.

[Long-term evaluation of bilateral alveolar bone grafting]

OBJECTIVE

To evaluate the long-term result of the bilateral alveolar bone grafting.

METHODS

Fifty-five consecutive complete bilateral cleft lip and palate patients (36 males and 19 females) who had alveolar bone grafting were included in this study. The total number of cleft sites was 110. Cancellous bone from the iliac crest was grafted into the alveolar cleft areas. The cleft sites were studied in two groups according to whether the cleft canine had erupted prior to bone grafting or not. Anterior occlusal radiographs were taken before and after bone grafting. The minimum period of observation after alveolar bone grafting was one year. Criteria described by Bergland et al. (1986) were utilised to assess the height of the interdental septum.

RESULTS

The results showed that bone grafting before canine eruption has a higher clinical success rate (95%) compared with that carried out after canine eruption (67%).

CONCLUSION

The critical variable affecting the quality of bilateral alveolar bone grafting is the timing of the surgery.

Stochastic resonance in a bistable system subject to multiplicative and additive noise

The stochastic resonance (SR) phenomenon in a bistable system under the simultaneous action of multiplicative and additive noise and periodic signal is studied by using the theory of signal-to-noise ratio (SNR) in the adiabatic limit. Two cases have been considered: the case of no correlations between multiplicative and additive noise and the case of correlations between two noises. The expressions of the SNR for both cases are obtained. The effects of intensity of multiplicative and additive noise and the intensity of the correlations between noises on the SNR are discussed for both cases, respectively. It is found that the existence of a maximum in the SNR is the identifying characteristic of the SR phenomenon. In the case of no correlations between multiplicative and additive noise, the SNR is independent of the initial condition of the system. However, the SNR is not only dependent on the intensity of correlations between noises, but also on the initial condition of the system in the presence of correlations between two noises.

[Determination of trace elements in pure metal by optical emission spectrometry]

The important factor for trace concentration element analysis by optical emission spectrometry is detection limit, RSD, stability. Through study on analytical parameters of trace element in pure metal, it is found that the detection limit of element mainly depends on the choose analytical line and discharge type but bears no relation to reference. RSD and stability of analysis depend on analytical line pair(analytical line/reference line) and discharge type. The best analytical parameter will be selected to make quick and accurate analysis with this principle.

Direct interaction of resistance gene and avirulence gene products confers rice blast resistance

Rice expressing the Pi-ta gene is resistant to strains of the rice blast fungus, Magnaporthe grisea, expressing AVR-Pita in a gene-for-gene relationship. Pi-ta encodes a putative cytoplasmic receptor with a centrally localized nucleotide-binding site and leucine-rich domain (LRD) at the C-terminus. AVR-Pita is predicted to encode a metalloprotease with an N-terminal secretory signal and pro-protein sequences. AVR-Pita(176) lacks the secretory and pro-protein sequences. We report here that transient expression of AVR-Pita(176) inside plant cells results in a Pi-ta-dependent resistance response. AVR-Pita(176) protein is shown to bind specifically to the LRD of the Pi-ta protein, both in the yeast two-hybrid system and in an in vitro binding assay. Single amino acid substitutions in the Pi-ta LRD or in the AVR-Pita(176) protease motif that result in loss of resistance in the plant also disrupt the physical interaction, both in yeast and in vitro. These data suggest that the AVR-Pita(176) protein binds directly to the Pi-ta LRD region inside the plant cell to initiate a Pi-ta-mediated defense response.

[Clinical study on Zhuyu Xiaozhong mixture combined with stereotaxic drainage in treating hypertensive cerebral hemorrhage]

OBJECTIVE

To explore the effective method of integrated traditional Chinese and western medicine (TCM-WM) therapy in treating hypertensive cerebral hemorrhage (HCH).

METHODS

Sixty-one HCH patients were randomly divided into two groups: the treated group (group A, 31 cases) and the control group (group B, 30 cases), the former group was treated with stereotaxic drainage and orally taken Zhuyu Xiaozhong mixture (ZYXZM), and the latter group with stereotaxic drainage alone.

RESULTS

The total effective rate of group A was 83.9%, significantly higher than that of group B (60.0%, P < 0.05). In comparing the two groups, the neurological function recovery, the quality of life and the hematoma absorption in group A were significantly better than those of group B (P < 0.05).

CONCLUSION

ZYXZM combined with stereotaxic drainage is effective in treating HCH. It could promote the neurological function recovery and improve the quality of life as well.

[Terminal differentiation of human acute promyelocytic leukemia (APL) cells induced by Tanshinone II A in primary culture]

The aim of this study was to investigate whether Tanshinone II A (Tan II A) can induce human acute promyelocytic leukemia (APL) cells to differentiate or not in primary culture. The APL cells from 5 cases were cultured respectively with Tan II A at the concentration of 0.5 microgram/ml for 7 days in vitro. The differentiations of these leukemia cells were observed cytomorphologically and examined by nitroblue tetrazolium (NBT) test. The cell DNA cycle and membrane cluster differentiation (CD) antigens (CD33, CD11b) were analyzed by flow cytometry. The results showed that 82.5% +/- 4.8% of APL cells were induced into morphologically and functionally differentiated cells. The cell growth curve showed that the growth of APL cells was inhibited. The degree of differentiation and growth inhibition induced by Tan II A was not different from that by ATRA (P > 0.05). Flow cytometry analysis showed that Tan II A arrested APL cells in G0/G1 phase and inhibited cellular DNA synthesis. This study demonstrates that Tan II A can induce differentiation of APL cells in vitro, and hence it is worthy of further studies for clinical use.

Deletion of PBP/PPARBP, the gene for nuclear receptor coactivator peroxisome proliferator-activated receptor-binding protein, results in embryonic lethality

We previously isolated and identified peroxisome proliferator-activated receptor (PPAR)-binding Protein (PBP) as a coactivator for PPARgamma. PBP has recently been identified as a component of the multiprotein complexes such as TRAP, DRIP, and ARC that appear to play an important role in the transcriptional activation by several transcriptional factors including nuclear receptors. To assess the biological significance of PBP, we disrupted the PBP gene (PBP/PPARBP) in mice by homologous recombination. PBP(+/-) mice are healthy, fertile, and do not differ significantly from PBP(+/+) control littermates. PBP null mutation (PBP(-/-)) is embryonically lethal at embryonic day 11.5, suggesting that PBP is an essential gene for mouse embryogenesis. The embryonic lethality is attributed, in part, to defects in the development of placental vasculature similar to those encountered in PPARgamma mutants. Transient transfection assays using fibroblasts isolated from PBP mutant embryos revealed a decreased capacity for ligand-dependent transcriptional activation of PPARgamma as compared with fibroblasts derived form the wild type embryos. These observations suggest that there is no functional redundancy between PBP and other coactivators such as steroid receptor coactivator-1 and that PBP plays a critical role in the signaling of PPARgamma and other nuclear receptors.

Nicotine reverses GABAergic inhibition of long-term potentiation induction in the hippocampal CA1 region

Nicotine is known to enhance cognitive function but the mechanism is unknown. The present study examined the modulatory effect of nicotine on the induction of long-term potentiation (LTP), a synaptic model of learning and memory. A weak tetanic stimulation consisting of 20 pulses at 100 Hz induced stable LTP in the hippocampal CA1. The induction of LTP was completely blocked if the tetanus was delivered in the presence of muscimol (2.5 microM), a gamma-aminobutyric acid (GABA) receptor agonist. This inhibition was sensitive to, and reversed by, not only nicotinic acetylcholine receptor (nAChR) agonists (nicotine and epibatidine), but also the alpha7 nAChR-selective antagonist methyllycaconitine (MLA). Furthermore, ACh-puff activation of alpha7 nAChRs on feedforward interneurons induced inhibitory postsynaptic currents in pyramidal cells that were blocked by nicotine or MLA. In addition, nicotine reduced field monosynaptic inhibitory postsynaptic potentials in the presence of MLA. These results suggest not only two pathways of nicotine-induced disinhibition of pyramidal cells, one involving desensitization of alpha7 nAChRs and the other involving non-alpha7 nAChRs, but also two potential mechanisms underlying the modulatory effect of nicotine on LTP induction, both reducing GABAergic inhibition, thereby indirectly increasing the excitability of pyramidal cells.

Lipases provide a new mechanistic model for polyhydroxybutyrate (PHB) synthases: characterization of the functional residues in Chromatium vinosum PHB synthase

Polyhydroxybutyrate (PHB) synthases catalyze the conversion of beta-hydroxybutyryl coenzyme A (HBCoA) to PHB. These enzymes require an active site cysteine nucleophile for covalent catalysis. A protein BLASTp search using the Class III Chromatium vinosum synthase sequence reveals high homology to prokaryotic lipases whose crystal structures are known. The homology is very convincing in the alpha-beta-elbow (with the active site nucleophile)-alpha-beta structure, residues 131-175 of the synthase. A conserved histidine of the Class III PHB synthases aligns with the active site histidine of the lipases using the ClustalW algorithm. This is intriguing as this histidine is approximately 200 amino acids removed in sequence space from the catalytic nucleophile. Different threading algorithms suggest that the Class III synthases belong to the alpha/beta hydrolase superfamily which includes prokaryotic lipases. Mutagenesis studies were carried out on C. vinosum synthase C149, H331, H303, D302, and C130 residues. These studies reveal that H331 is the general base catalyst that activates the nucleophile, C149, for covalent catalysis. The model indicates that C130 is not involved in catalysis as previously proposed [Müh, U., Sinskey, A. J., Kirby, D. P., Lane, W. S., and Stubbe, J. (1999) Biochemistry 38, 826-837]. Studies with D302 mutants suggest D302 functions as a general base catalyst in activation of the 3-hydroxyl of HBCoA (or a hydroxybutyrate acyl enzyme) for nucleophilic attack on the covalently linked thiol ester intermediate. The relationship of the lipase model to previous models based on fatty acid synthases is discussed.

Triterpenoids from Tripterygium wilfordii

The extract (T(II)) of Tripterygium wilfordii Hook f. afforded four triterpenoids: wilforic acid D (3beta,24-epoxy-2alpha-hydroxy-24R*-ethoxy-29-friedelanoic acid); (E) 3beta,24-epoxy-2-oxo-3alpha-hydroxy-29-friedelanoic acid; (F) 2beta-hydroxy-3-oxo-friedelan-29-oic acid; 29-hydroxy-3-oxo-olean-12-en-28-oic acid and 17 known triterpenoids. Their structures were established on the basis of spectroscopic studies. In a bioactivity analysis, only the known dulcioic acid compound showed a significant inhibitory effect on cytokine production.

Sesquiterpene alkaloids from Tripterygium hypoglaucum and Tripterygium wilfordii: a new class of potent anti-HIV agents

Five new sesquiterpene pyridine alkaloids [triptonines A (1) and B (2), and wilfordinines A (3), B (4), and C (5)] and two known compounds (peritassine A and hypoglaunine C) were isolated from Tripterygium hypoglaucum and a clinically used extract of Tripterygium wilfordii. The structures of 1-5 were elucidated by spectroscopic methods. The anti-HIV activity of 1, 2, and several related compounds was evaluated. Triptonine B (2) demonstrated potent anti-HIV activity with an EC(50) value of <0.10 microg/mL and an in vitro therapeutic index value of >1000.

[Acute promyelocytic leukemia cell differentiation induced by tanshinone II A and its molecular mechanism]

OBJECTIVE

To investigate APL cell differentiation induced by tanshinone II (Tan II A) and its molecular mechanism.

METHODS

In vitro incubation of NB4 cells with Tan II A at the concentration of 0.5 microg/ml for 5 days, the cell differentiation was observed by cytomorphology, and nitroblue tetrazolium (NBT) test. Cell cycle, membrane CD(33), CD(11b) antigens and gene expressions (c-myc, c-fos, p53 and bcl-2) were analysed by flow cytometry.

RESULTS

(91.3 +/- 2.1)% of NB4 cells were induced into morphologically and functionally more differentiated cells including 0.26 of myelocytes and metamyelocytes, and 0.68 of band form and neutrophils. Cell growth curve showed that growth of NB4 cells were inhibited. NBT reduction was significantly increased. Expression of CD(33) decreased and CD(11b) increased. The degrees of cell differentiation and growth inhibition induced by Tan II A or ATRA were no difference. Flow cytometry analysis showed that Tan II A arrested NB4 cell in G(0)/G(1) phase, inhibited cellular DNA synthesis, down-regulated c-myc and bcl-2 genes expression, and up-regulated c-fos and p53 genes expression.

CONCLUSION

Tan II A can induce differentiation and growth inhibition of NB4 cells. Its possible molecular mechanism might relate to modulation of gene expressions associated proliferation and differentiation, and to inhibition of DNA synthesis.

[Effects of protocol HX-97 on mobilization, collection and hematopoietic reconstitution of peripheral blood stem cells transplantation]

In order to enhance the effects of peripheral blood stem cell mobilization, collection and hematopoietic reconstitution, we observed and evaluated the effects of Protocol HX-97 on 22 patients who received allogeneic or autologous peripheral blood stem cell transplants from April 1997 to June 1999. rhG-CSF was used for mobilization at a dose of 300 micrograms/day for 6 days; the sixth dose was given an hour and a half before leukapheresis. High dose chemotherapy and rhG-CSF were given for autologous peripheral blood stem cell mobilization; the chemotherapy should be intensive enough to reduce the patients' peripheral WBC to less than 1.0 x 10(9)/L, and the beginning of using rhG-CSF should be just at the time of WBC's rising from the nadir. rhGM-CSF and rhG-CSF were given sequentially for hematopoietic reconstitution after transplantation. The results showed that leukaphereses were successfully performed for peripheral blood stem cell collection. Sixteen cases needed apheresis only once, and 6 cases needed it twice. The harvests were 2.5-10.7 x 10(8)/kg MNC, 2.5-20.0 x 10(6)/kg CD34+ cells (including 1.8-7.5 x 10(6)/kg CD34+CD33-, 0.7-12.5 x 10(6)/kg CD34+CD33+), and 3.5-6.3 x 10(5)/kg CFU-GM. Hematopoietic function recovered to > 0.5 x 10(9)/L of neutrophil count in allo-PBSCT at 14-20 days and in auto-PBSCT at 12-20 days, and to > 20 x 10(9)/L of platelet count in allo-PBSCT and in auto-PBSCT at 16-34 days and 16-28 days, respectively. At day +30 post-transplantation, chromosome analysis and DNA finger print assessment of bone marrow cells indicated that the patients' hematopoietic function had been reconstituted. This study suggests that Protocol HX-97 is an effective approach to mobilization of peripheral blood stem cell transplantation, and it is relatively cost-effective.

[Effect of dingxin recipe on arrhythmia and injury induced by ischemia and reperfusion in rabbits]

OBJECTIVE

To investigate the protective effect of Dingxin Recipe (DXR) on arrhythmia and injury induced by ischemia and reperfusion.

METHODS

Rabbits were randomly divided into four groups and administered orally with DXR of high dose, low dose, propanolol and distilled water. Two-step coronary artery ligature was used to form ischemia and reperfusion model. Superoxide dismutase (SOD), cyclic adenosine monophosphate (cAMP), norepinephrine (NE), dopamine (DA), 5-hydroxytryptamine (5-HT), myocyte ultrastructural injury and occurrence of arrhythmia were investigated.

RESULTS

DXR could obviously antagonize arrhythmia induced by myocardial infarction or ischemia and reperfusion in rabbits. Compared with the control group, DXR of high and low doses could improve the changes in ST-T. In rabbits treated with DXR, the levels of SOD were elevated while cAMP, NE, DA, 5-HT and the whole blood viscosity were lowered.

CONCLUSIONS

DXR could obviously antagonize arrhythmia and injury induced by ischemia and reperfusion, DXR may clear oxygen free radical, regulate the second messenger, inhibit sympathetic nerve system, improve local circulation, protect mitochondria and prevent the activation of lysosome and safeguard the cardiac myocyte to be free from injury.

Changes in serum cardiac troponin I levels after percutaneous transluminal coronary angioplasty

OBJECTIVE

To evaluate the possible effect of percutaneous transluminal coronary (PTCA) on myocardium.

METHODS

Serum cTnl and CK-MB were measured in 60 patients with coronary artery disease (CAD) who underwent PTCA before and at the 6th, 12th, 24th, 48th and 72nd hour after the interventional procedure respectively.

RESULTS

The serum cTnl levels began to increase at 6 hours (9.65 +/- 6.27 micrograms/L) in 18 patients, reached the peak levels during 12-24 hours (20.43 +/- 11.28 micrograms/L, 18.52 +/- 9.52 micrograms/L), and returned to normal range till 48-72 hours (7.35 +/- 7.62 micrograms/L, 5.51 +/- 3.13 micrograms/L) after PTCA. The serum cTnl and CK-MB levels were kept normal range pre- and post-PTCA in 30 cases. The levels of cTnl in 12 cases were over baseline either before or after the procedure, while for CK-MB, only in 3 cases were over normal range after PTCA. Compared with normal cTnl group, elevated cTnl levels were related to total inflation times and dilated times (P < 0.05).

CONCLUSIONS

PTCA may cause some minor damage in myocardium, serum cTnl level was more sensitive and specific for monitoring myocardial injury.

Immunosuppressive diterpenoids from Tripterygium wilfordii

A clinically used extract of Tripterygium wilfordii afforded three new diterpenoids-3beta,19-dihydroxyabieta-8,11,13-triene (triptobenzene L) (1); 12,19-dihydroxy-3-oxoabieta-8,11,13-triene (triptobenzene M) (2); and 19-hydroxy-3,7-dioxo-abieta-8,11, 13-triene (triptobenzene N) (3)-along with 14 known diterpenoids. The structures of 1-3 were established on the basis of spectroscopic studies. Of the known compounds, the stereochemistry at C-4 of triptonediol (4) was reassigned. Tripterifordin (8) and 13-epi-manoyl oxide-18-oic acid (9) showed significant inhibitory effects on cytokine production.

Insight into the mechanism of phosphoenolpyruvate mutase catalysis derived from site-directed mutagenesis studies of active site residues

PEP mutase catalyzes the conversion of phosphoenolpyruvate (PEP) to phosphonopyruvate in biosynthetic pathways leading to phosphonate secondary metabolites. A recent X-ray structure [Huang, K., Li, Z., Jia, Y., Dunaway-Mariano, D., and Herzberg, O. (1999) Structure (in press)] of the Mytilus edulis enzyme complexed with the Mg(II) cofactor and oxalate inhibitor reveals an alpha/beta-barrel backbone-fold housing an active site in which Mg(II) is bound by the two carboxylate groups of the oxalate ligand and the side chain of D85 and, via bridging water molecules, by the side chains of D58, D85, D87, and E114. The oxalate ligand, in turn, interacts with the side chains of R159, W44, and S46 and the backbone amide NHs of G47 and L48. Modeling studies identified two feasible PEP binding modes: model A in which PEP replaces oxalate with its carboxylate group interacting with R159 and its phosphoryl group positioned close to D58 and Mg(II) shifting slightly from its original position in the crystal structure, and model B in which PEP replaces oxalate with its phosphoryl group interacting with R159 and Mg(II) retaining its original position. Site-directed mutagenesis studies of the key mutase active site residues (R159, D58, D85, D87, and E114) were carried out in order to evaluate the catalytic roles predicted by the two models. The observed retention of low catalytic activity in the mutants R159A, D85A, D87A, and E114A, coupled with the absence of detectable catalytic activity in D58A, was interpreted as evidence for model A in which D58 functions in nucleophilic catalysis (phosphoryl transfer), R159 functions in PEP carboxylate group binding, and the carboxylates of D85, D87 and E114 function in Mg(II) binding. These results also provide evidence against model B in which R159 serves to mediate the phosphoryl transfer. A catalytic motif, which could serve both the phosphoryl transfer and the C-C cleavage enzymes of the PEP mutase superfamily, is proposed.

Interactions of the integrase protein of the conjugative transposon Tn916 with its specific DNA binding sites

The binding of two chimeric proteins, consisting of the N-terminal or C-terminal DNA binding domain of Tn916 Int fused to maltose binding protein, to specific oligonucleotide substrates was analyzed by gel mobility shift assay. The chimeric protein with the N-terminal domain formed two complexes of different electrophoretic mobilities. The faster-moving complex, whose formation displayed no cooperativity, contained two protein monomers bound to a single DNA molecule. The slower-moving complex, whose formation involved cooperative binding (Hill coefficient > 1.0), contained four protein monomers bound to a single DNA molecule. Methylation interference experiments coupled with the analysis of protein binding to mutant oligonucleotide substrates showed that formation of the faster-moving complex containing two protein monomers required the presence of two 11-bp direct repeats (called DR2) in direct orientation. Formation of the slower-moving complex required only a single DR2 repeat. Binding of the N-terminal domains in vivo could serve to position two Int monomers on the DNA near each end of the transposon and assist in bringing together the ends of the transposon so that excision can occur. The chimeric protein with the C-terminal domain of Int also formed two complexes of different electrophoretic mobilities. The major, slower-moving complex, whose formation involved cooperative binding, contained two protein molecules bound to one DNA molecule. This finding suggested that while the C-terminal domain of Int can bind DNA as a monomer, a cooperative interaction between two monomers of the C-terminal domain may help to bring the ends of the transposon together during excision.

Signalling between mitochondria and the nucleus regulates the expression of a new D-lactate dehydrogenase activity in yeast

We have adapted a LacZ promoter trap screen developed by Burns et al. (1994) to search for genes whose expression is dependent on Rtg2p, a protein with an N-terminal hsp70/actin/sugar kinase ATP binding domain. Rtg2p acts upstream of the basic helix-loop-helix/leucine zipper transcription factors, Rtg1p and Rtg3p. All three proteins are known to be required for the expression of the CIT2 gene, which encodes a peroxisomal isoform of citrate synthase whose expression is also dependent on the functional state of mitochondria. Using this screen, we have identified a previously uncharacterized gene, YEL071w, predicted to encode a protein of 496 amino acids that shares 80% homology and 60% sequence identity with actin interacting protein 2, encoded by the AIP2 gene; both proteins also share sequence similarity to aD-lactate dehydrogenase encoded by the DLD1 gene. Expression of YEL071w is dependent on the functional state of mitochondria and on all three of the Rtg proteins, whereas AIP2 expression is independent of the Rtg proteins and the functional state of mitochondria. Like CIT2, the 5' flanking region of YEL071w contains two R box binding sites for the Rtg1p/Rtg3p heterodimeric transcription complex. Both R boxes are necessary for full YEL071w expression. We show that YEL071w and AIP2 encode proteins withD-lactate dehydrogenase activity, the former located in the cytoplasm and the latter in the mitochondrial matrix. Our data thus provide gene assignments for two previously unrecognized D-lactate dehydrogenase activities in yeast.

Crystal structure of the complex formed between bovine beta-trypsin and MCTI-A, a trypsin inhibitor of squash family, at 1.8-A resolution

The stoichiometric complex formed between bovine beta-trypsin and Momordica charantia, Linn. Cucurbitaceae trypsin inhibitor A (MCTI-A) was crystallized and its X-ray crystal structure was refined to a final R value of 0.179 using data of 7.0- to 1.8-A resolution. Combination with results on the complex of MCTI-A with porcine trypsin gives the sequence of MCTI-A definitely, of which 13 residues are conserved compared with other squash family trypsin inhibitors. Its spatial structure and the conformation of its primary binding segment from Cys3I (P3) to Glu7I (P3'), which contains a reactive scissile bond Arg5I C-Ile6I N, were found to be very similar to the other squash family proteinase inhibitors.

[Clinical manifestations and CT diagnosis of non-allergic fungal sinusitis]

OBJECTIVE

The diagnose of fungal sinusitis, especially complicated by bone destructive, and its differential diagnosis from malignant tumour of nasal sinus were studied.

METHOD

Five cases were diagnosed with CT; nasal sinus microsurgery was done in 4 cases and sinusotomy in one case. None of them were treated by antifungal agents.

RESULT

Fungal filaments were postoperatively shown in 5 pathological reports, fungal spores in some cases. No recurrence and complications occurred as followed from 6 months to 3 years.

CONCLUSION

It is not easy to differentiate fungal sinusitis from malignant tumour of nasal sinus, sometimes, but CT has demonstrated its importance of diagnostic value.

Rapid transcript accumulation of pathogenesis-related genes during an incompatible interaction in bacterial speck disease-resistant tomato plants

In the yeast two-hybrid system, the Pto kinase interacts with three putative transcription factors Pti4, Pti5 and Pti6. The Pti4/5/6 proteins contain a DNA binding domain that recognizes and binds a DNA sequence (5'-AGCCGCC3'; the 'PR box') present in the promoter region of a large number of genes encoding 'pathogenesis-related' (PR) proteins. We have now investigated the pathogen-induced expression of PR box-containing genes in tomato. We isolated a tomato osmotin gene that contains two PR boxes in its promoter region and demonstrated that the abundance of the osmotin transcript rapidly increases during an incompatible interaction involving Pro-containing tomato plants and the bacterial pathogen Pseudomonas syringae pv. tomato expressing the avrPto gene. In addition, we found that transcripts of two other tomato PR genes (encoding endochitinase and beta-1,3-glucanase B) and at least one ACC oxidase gene, all of which contain PR boxes in their promoter regions, rapidly accumulate in the incompatible interaction. These data support the hypothesis that the tomato Pto kinase regulates the expression of certain defense genes in tomato by interaction with transcription factors that bind the PR box.

Helix swapping between two alpha/beta barrels: crystal structure of phosphoenolpyruvate mutase with bound Mg(2+)-oxalate

BACKGROUND

Phosphonate compounds are important secondary metabolites in nature and, when linked to macromolecules in eukaryotes, they might play a role in cell signaling. The first obligatory step in the biosynthesis of phosphonates is the formation of a carbon-phosphorus bond by converting phosphoenolpyruvate (PEP) to phosphonopyruvate (P-pyr), a reaction that is catalyzed by PEP mutase. The PEP mutase functions as a tetramer and requires magnesium ions (Mg2+).

RESULTS

The crystal structure of PEP mutase from the mollusk Mytilus edulis, bound to the inhibitor Mg(2+)-oxalate, has been determined using multiwavelength anomalous diffraction, exploiting the selenium absorption edge of a selenomethionine-containing protein. The structure has been refined at 1.8 A resolution. PEP mutase adopts a modified alpha/beta barrel fold, in which the eighth alpha helix projects away from the alpha/beta barrel instead of packing against the beta sheet. A tightly associated dimer is formed, such that the two eighth helices are swapped, each packing against the beta sheet of the neighboring molecule. A dimer of dimers further associates into a tetramer. Mg(2+)-oxalate is buried close to the center of the barrel, at the C-terminal ends of the beta strands.

CONCLUSIONS

The tetramer observed in the crystal is likely to be physiologically relevant. Because the Mg(2+)-oxalate is inaccessible to solvent, substrate binding and dissociation might be accompanied by conformational changes. A mechanism involving a phosphoenzyme intermediate is proposed, with Asp58 acting as the nucleophilic entity that accepts and delivers the phosphoryl group. The active-site architecture and the chemistry performed by PEP mutase are different from other alpha/beta-barrel proteins that bind pyruvate or PEP, thus the enzyme might represent a new family of alpha/beta-barrel proteins.

Prenatal nicotine increases pulmonary alpha7 nicotinic receptor expression and alters fetal lung development in monkeys

It is well established that maternal smoking during pregnancy is a leading preventable cause of low birth weight and prematurity. Less appreciated is that maternal smoking during pregnancy is also associated with alterations in pulmonary function at birth and greater incidence of respiratory illnesses after birth. To determine if this is the direct result of nicotine interacting with nicotinic cholinergic receptors (nAChRs) during lung development, rhesus monkeys were treated with 1 mg/kg/day of nicotine from days 26 to 134 of pregnancy. Nicotine administration caused lung hypoplasia and reduced surface complexity of developing alveoli. Immunohistochemistry and in situ alpha-bungarotoxin (alphaBGT) binding showed that alpha7 nAChRs are present in the developing lung in airway epithelial cells, cells surrounding large airways and blood vessels, alveolar type II cells, free alveolar macrophages, and pulmonary neuroendocrine cells (PNEC). As detected both by immunohistochemistry and by alphaBGT binding, nicotine administration markedly increased alpha7 receptor subunit expression and binding in the fetal lung. Correlating with areas of increased alpha7 expression, collagen expression surrounding large airways and vessels was significantly increased. Nicotine also significantly increased numbers of type II cells and neuroendocrine cells in neuroepithelial bodies. These findings demonstrate that nicotine can alter fetal monkey lung development by crossing the placenta to interact directly with nicotinic receptors on non-neuronal cells in the developing lung, and that similar effects likely occur in human infants whose mothers smoke during pregnancy.

Peptidyl transferase center activity observed in single ribosomes

We demonstrate the functional activity of single ribosomal complexes, opening the way for detailed studies of the trajectories of protein synthesis. Our approach employs a single-molecule detection system, capable of picoseconds to minutes resolution, to observe a growing peptide labeled at its N terminus with the fluorophore tetramethylrhodamine (TMR). Single complexes of mRNA-programmed ribosomes with TMR-Met-tRNAMetf or TMR-Met-Phe-tRNAPhe are immobilized on mica and observed by fluorescence. Immobilized ribosome.mRNA.TMR-Met-tRNAMetf complexes form peptide bonds with puromycin. Single-molecule detection reveals dynamics on the scale of seconds at the ribosomal peptidyl transferase center.

X-ray studies on two forms of bovine beta-trypsin crystals in neat cyclohexane

Two orthorhombic forms (Vm values are 2.3 and 3.0 A3/Da) of bovine beta-trypsin crystals in neat cyclohexane were determined to 1.93 A resolution, by X-ray diffraction. Both structures in organic solvent are similar to those in aqueous solution. In the high packing density form, one cyclohexane molecule is found in a hydrophobic site near the active center. One sulfate locates at the active site with hydrogen or salt bond to the Ser-His catalytic diad, and five more sulfates bind on the molecular surface. The conformation of the side chains near the sulfates changed greatly. In the low packing density form, one cyclohexane and three sulfates are found. In both structures, one benzamidine molecule locates at the hydrophobic pocket of the active center. Most water molecules on the enzyme surface are retained except some with high temperature factors.

[MMC conditioning regimen (Melphalan, MeCCNU and cyclophosphamide) followed by allogeneic peripheral blood stem cells transplantation for chronic myeloid leukemia]

This paper reports 3 cases of allogeneic peripheral blood stem cell transplantation (Allo-PBSCT) for the patients with chronic myeloid leukemia (CML). The patients received MMC preparative regimen with high dose chemotherapy (Melphalan 170 mg/m2, p.o. on Day-5, MeCCNU 400 mg/m2, p.o. on Day-4, and Cyclophosphomide 60 mg/kg/day, i.v. on Days-3 and -2). The HLA-identical sibling donors received filgrastim (rhG-CSF) for mobilization at a dose of 300 micrograms/day for 6 days. Leukaphereses were done at the 6th day of mobilization. A median of 8000 ml (2 times total blood volume) of blood was processed the collecting: 2.5-4.5 x 10(8)/kg MNC, 12.8-20.0 x 10(6)/kg CD34+ cells (including 4.8-7.5 x 10(6)/kg CD34+CD33-, 8.0-13.0 x 10(6)/kg CD34+CD33+), and 3.5-4.3 x 10(5)/kg CFU-GM. Cyclosporin A and methotrexate were used for GVHD prophylaxis. Hematopoitic function recovered as for 14-20 days to > 0.5 x 10(9)/L of neutrophil count, and for 16-34 days to > 20 x 10(9)/L of platelet count. At day + 100, chromosome analysis of bone marrow cells showed that complete chimera without ph1 positive chromosome in Cases 1 and 3, and a partial chimera with 73% donor karyotype in Case 2. All patients now are in disease free survival. No episode of acute graft versus host disease (GVHD) developed. It was concluded that HLA matched sibling allogeneic PBSCT result in rapid hematopoitic reconstitution and the MMC conditioning regimen is effective both in leukemic cells eradication and in immunosuppression for stem cells engraftment, and the drug related toxicity could be tolerated by patients.

Clinical research on the therapeutic effect of the electro-acupuncture treatment in patients with depression

Electroacupuncture (EA) stimulation has been found to influence the brain (norepinephrine metabolism in experimental animals). Preliminary clinical research has shown that EA treatment is as effective as amitriptyline for patients with depression. In this study, two consecutive clinical studies on the treatment of depression with EA are conducted. The first study was double blind placebo controlled, in which 29 depressed inpatients were recruited. Patients were randomly divided into three groups: EA + placebo; amitriptyline; and EA + amitriptyline. They received EA and/or amitriptyline treatment for 6 weeks. The Hamilton Rating Scale for Depression, Clinical Global Impression and ASBERG scales for the side effect of antidepressants were used to evaluate the therapeutic efficacy and side effects. Based on the results and research protocol of the first study, a multi-centered collaborative study was conducted, in which 241 inpatients with depression were recruited. Patients were randomly divided into two treatment groups: the EA + placebo and the amitriptyline groups. The results from both studies showed that the therapeutic efficacy of EA was equal to that of amitriptyline for depressive disorders (P > 0.05). Electro-acupuncture had a better therapeutic effect for anxiety somatization and cognitive process disturbance of depressed patients than amitriptyline (P < 0.05). Moreover, the side effects of EA were much less than that of amitriptyline (P < 0.001). The article suggested that EA treatment was an effective therapeutic method for depressive disorders. Particularly, it was a treatment of choice for depressed patients who were unable to comply with the classic tricyclic antidepressants because of their anticholinergic side effects. The possible mechanism of EA treatment is discussed.

Nitric oxide synthesis by tracheal smooth muscle cells by a nitric oxide synthase-independent pathway

Nitric oxide (NO) is known to be synthesized from L-arginine in a reaction catalyzed by NO synthase. Liver cytochrome P-450 enzymes also catalyze the oxidative cleavage of C==N bonds of compounds containing a -C(NH2)==NOH function, producing NO in vitro. The present study was designed to investigate whether there was evidence of a similar pathway for the production of NO in tracheal smooth muscle cells. Formamidoxime (10(-2) to 10(-4) M), a compound containing -C(NH2)==NOH, relaxed carbachol-contracted tracheal rings and increased intracellular cGMP in cultured tracheal smooth muscle cells, whereas L-arginine had no such effect. NO was detectable in the medium containing cultured tracheal smooth muscle cells when incubated with formamidoxime. Ethoxyresorufin (10(-7) to 10(-4) M), an alternate cytochrome P-450 substrate, inhibited formamidoxime-induced cGMP accumulation as well as tracheal ring relaxation in cultured tracheal smooth muscle cells. The NO synthase inhibitors Nomega-nitro-L-arginine (10(-3) M) and NG-monomethyl-L-arginine (10(-3) M) had no effect on formamidoxime-induced cGMP accumulation. These results suggest that NO can be synthesized from formamidoxime in tracheal smooth muscle cells, presumably by a reaction catalyzed by cytochrome P-450.

Nociceptin/orphanin FQ binding increases in superficial laminae of the rat spinal cord during persistent peripheral inflammation

Regulation of nociceptin/orphanin FQ neurotransmission in conjunction with peripheral inflammation and hyperalgesia was explored, using receptor autoradiography. Binding of [3H]nociceptin was quantified in spinal segment L4 of rats at 2, 4 and 8 days following injection of complete Freund's adjuvant (CFA) into one hind-paw. Densitometric analysis of autoradiograms showed that [3H]nociceptin binding increased in medial and lateral laminae I-II bilaterally 4 days following injection of CFA compared to untreated rats; no change in binding occurred in lamina X at the times examined. Biochemical studies confirmed that the specific binding of [3H]nociceptin to sections of rat brain was consistent with the binding characteristics of the nociceptin receptor. These results suggest that spinal nociceptin receptors are upregulated during hyperalgesia. This response may enhance endogenous mechanisms of antinociception to attenuate the hyperalgesia induced by CFA.

X-ray studies on cross-linked lysozyme crystals in acetonitrile-water mixture

Tetragonal crystals of hen egg white lysozyme were cross-linked and subjected to X-ray diffraction study in acetonitrile-water media with different acetonitrile concentrations. Crystals in neat acetonitrile did not scatter X-ray well. Structures of crystals in neat water, in 90% and 95% acetonitrile, and crystal back-soaked from acetonitrile to water, were determined to about 2 A resolution. For crystals in both 90% acetonitrile, and crystal back-soaked from acetonitrile to water, were determined to about 2 A resolution. For crystals in both 90% and 95% acetonitrile, only one protein-bond acetonitrile molecule is found in the active site cleft, and its location and binding-protein mode is similar to the C subunit of polysaccharide. The alteration in conformation and hydrogen-bond pattern involving water as solvent causes the reduction of the protein's flexibility in organic media. The back-soaked crystal regained its ordinary three-dimensional structure in water.

Requirements for p53 and the ATM gene product in the regulation of G1/S and S phase checkpoints

We investigated the requirements for protein p53 and the ATM gene product in radiation-induced inhibition of DNA synthesis and regulation of the cyclin E/ and cyclin A/cyclin dependent kinases (Cdks). Wild type (WT) mouse lung fibroblasts (MLFs), p53(-/-) knock-out MLFs, normal human skin fibroblasts (HSF-55), and human AT skin fibroblasts (GM02052) were used in the investigations. The absence of p53 had no significant effect on the inhibition or recovery of DNA synthesis throughout the S phase, as determined from BrdU labeling and flow cytometry, or the rapid inhibition of cyclin A/Cdks. Gamma radiation (8 Gy) inhibited DNA synthesis and progression into G2 during the first 3 h after irradiation, and the recovery of these processes occurred at similar rates in both WT and p53(-/-) MLFs. The cyclin A/Cdks were inhibited 55-70% at 1 h after irradiation in both cell types, but p21WAF1/Cip1 levels or p21 interaction with Cdk2 did not increase in the irradiated p53(-/-) MLFs. Although p53(-/-) MLFs do not exhibit prolonged arrest at a G1 checkpoint, radiation did induce a rapid 20% reduction and small super-recovery of cyclin E/Cdk2 within 1-2 h after irradiation. Similar inhibition and recovery of cyclin E/Cdk2 previously had been associated with regulation of transient G1 delay and the inhibition of initiation at an apparent G1/S checkpoint in Chinese hamster cells. In contrast, loss of the ATM gene product abrogated transient cyclin E/Cdk2 inhibition, most inhibition of DNA synthesis and all, but a 10-15% inhibition, of the cyclin A/Cdks. The results indicate that neither p53 nor p21 is required for transient inhibition of cyclin E/Cdk2 associated with the G1/S checkpoint or for inhibition of DNA synthesis at 'checkpoints' within the S phase. Conversely, the ATM gene product appears to be essential for regulation of the G1/S checkpoint and for inhibition of DNA replication associated with the inhibition of cyclin A/Cdk2. Differential aspects of DNA synthesis inhibition among cell types are presented and discussed in the context of S phase checkpoints.

[A study on enzymatic activities of bronchoalveolar lavage fluid in patients with interstitial lung diseases]

OBJECTIVE

To evaluate the relationship between enzymatic activities in bronchoalveolar lavage fluid(BALF) and interstitial lung diseases(ILDs).

METHOD

Cellular components and levels of superoxide dismutase (SOD), glutathione peroxidase(GSH-PX), angiotensin converting enzyme(ACE) and lactate dehydrogenase(LDH) in BALF in 30 cases of ILDs: including 18 patients with idiopathic pulmonary fibrosis (IPF) and 12 patients with sarcoidosis (Sarc) and 9 healthy controls were determined.

RESULT

(1) The levels of BALF-SOD, GSH-PX were significantly decreased(P < 0.01), and BALF-ACE, LDH were markedly increased (P < 0.05) in patients with IPF, and BALF-ACE were also increased in patients with Sarc(P < 0.05); (2) There were good correlation between ACE and percentage of lymphocyte (r1 = 0.6574, P < 0.05), and ratio of CD4+/CD8+ (r2 = 0.9544, P < 0.001) in BALF of Sarc group.

CONCLUSION

Determining enzymatic activities could be helpful to study pathogenesis and diagnosis of ILDs, BALF-ACE may be as a good marker of disease activity of Sarcoidosis.

SGD: Saccharomyces Genome Database

The Saccharomyces Genome Database (SGD) provides Internet access to the complete Saccharomyces cerevisiae genomic sequence, its genes and their products, the phenotypes of its mutants, and the literature supporting these data. The amount of information and the number of features provided by SGD have increased greatly following the release of the S.cerevisiae genomic sequence, which is currently the only complete sequence of a eukaryotic genome. SGD aids researchers by providing not only basic information, but also tools such as sequence similarity searching that lead to detailed information about features of the genome and relationships between genes. SGD presents information using a variety of user-friendly, dynamically created graphical displays illustrating physical, genetic and sequence feature maps. SGD can be accessed via the World Wide Web at http://genome-www.stanford.edu/Saccharomyces/

[The Raman scatting of carbon nanotubes]

Raman scattering measurements of the cathode deposite produced by carbon arc discharge method and graphite was repotred. The results indicate that the inner core of the deposite containing large quantities of carbon nanotubes undergoing crystallization process. Carbon nanotube is one kind of micro-crystal of quasi-graphite.

Kinetic mechanism of GTP binding and RNA synthesis during transcription initiation by bacteriophage T7 RNA polymerase

We have used stopped-flow and rapid chemical quench-flow methods to investigate the kinetics of the early steps during transcription initiation by bacteriophage T7 RNA polymerase. Most promoters of T7 RNA polymerase initiate with two GTPs. The kinetics of GTP binding was investigated by monitoring the fluorescence changes resulting from GTP binding to polymerase and fluorescent 2-aminopurine-containing promoter DNA complex. Scheme 1 was determined from studies of T7 Phi10 promoter at 25 degrees C, where (E.D)n represents the polymerase.DNA complex in different conformations. GTPE and GTPI represent the elongating and initiating GTP molecules incorporated at the +2 and +1 positions, respectively. Our studies show that GTP at the elongation site binds with at least 10-fold tighter affinity than the GTP at the initiation site. Two conformational changes were revealed upon GTP binding to the polymerase.2-aminopurine DNA complex. The first conformational change occurred upon GTP binding to the elongation site. This conformational change was reversible, and studies with partially melted DNA and incorrect NTPs suggested that it may represent a DNA melting and/or base pairing step. A second rate-limiting conformational change whose rate was same as the maximum rate of pppGpG synthesis occurred after two GTPs were bound. As with DNA polymerases, this rate-limiting conformational change probably occurs at each NMP incorporation event and may be involved in proper positioning of the initiation and the elongating GTPs within the polymerase active site to achieve efficient and accurate RNA synthesis.

Fluorescence and photobleaching dynamics of single light-harvesting complexes

Single light-harvesting complexes LH-2 from Rhodopseudomonas acidophila were immobilized on various charged surfaces under physiological conditions. Polarized light experiments showed that the complexes were situated on the surface as nearly upright cylinders. Their fluorescence lifetimes and photobleaching properties were obtained by using a confocal fluorescence microscope with picosecond time resolution. Initially all molecules fluoresced with a lifetime of 1 +/- 0.2 ns, similar to the bulk value. The photobleaching of one bacteriochlorophyll molecule from the 18-member assembly caused the fluorescence to switch off completely, because of trapping of the mobile excitations by energy transfer. This process was linear in light intensity. On continued irradiation the fluorescence often reappeared, but all molecules did not show the same behavior. Some LH-2 complexes displayed a variation of their quantum yields that was attributed to photoinduced confinement of the excited states and thereby a diminution of the superradiance. Others showed much shorter lifetimes caused by excitation energy traps that are only approximately 3% efficient. On repeated excitation some molecules entered a noisy state where the fluorescence switched on and off with a correlation time of approximately 0.1 s. About 490 molecules were examined.

Disease-associated mutations in cytoplasmic loops 1 and 2 of cystic fibrosis transmembrane conductance regulator impede processing or opening of the channel

Since little is known about the contribution to function of the N-terminal cytoplasmic loops (CL1, residues 139-194; CL2, residues 242-307) of cystic fibrosis transmembrane conductance regulator (CFTR), all nine point mutations identified in CLs 1 and 2 from patients with cystic fibrosis were reconstructed in the expression vector pcDNA3-CFTR and expressed transiently in COS-1 and HEK-293 cells and stably in Chinese hamster ovary (CHO) cells. Four amino acid substitutions retarded production of mature, fully glycosylated CFTR, suggesting that misprocessing of the channel causes the disease symptoms in the affected patients. Protein maturation could not be promoted by cell culture conditions of reduced temperature (26 degrees C). When properly processed mutants were evaluated for functional defects by the iodide efflux method, the G178R- and E193K-CFTR-expressing cell lines showed impaired anion translocation activities. Patch-clamp studies of single channels revealed that E193K variants had a significantly decreased open probability, which resulted from an increase in the mean closed time of the channels. This contrasted with a previous study of disease-associated point mutations in CL3 that mainly affected the mean open time. None of the maturation-competent CL 1 and 2 mutants had altered conductance. Thus, the N-terminal CLs appear not to contribute to the anion translocation pathway of CFTR; rather, mutations in CL1 can impede transition to the open state. Interestingly, the ability of the non-hydrolyzable ATP analogue adenylyl imidodiphosphate (AMP-PNP) to lock the channel into open bursts was abolished by the I148T and G178R amino acid substitutions.

Nonexponential kinetics of a single tRNAPhe molecule under physiological conditions

The fluorescence decay functions of individual, specifically labeled tRNAPhe molecules exhibit nonexponential character as a result of conformational dynamics occurring during the measurement on a single molecule. tRNAPhe conformational states that interchange much more slowly are evidenced by the distribution of lifetimes observed for many individual molecules. A structural model for the nonexponential decay indicates that the tRNAPhe-probe adduct fluctuates between two states, one of which provides conditions that quench the probe fluorescence.

The C. elegans gene pag-3 is homologous to the zinc finger proto-oncogene gfi-1

Mutations in the Caenorhabditis elegans gene pag-3 result in misexpression of touch receptor-specific genes in the BDU interneurons and in motility defects. We cloned pag-3 and found that the gene encodes a C2H2-type zinc finger protein related to the mammalian GFI-1 protein. Sequencing of the three pag-3 alleles showed that two apparent null alleles encode a nonsense mutation before the zinc fingers and a missense mutation in the fourth zinc finger that changes a coordinating histidine to a tyrosine. The third allele contains a nonsense mutation in the N-terminal region but is not a null allele. Northern analysis showed that a single pag-3 transcript of about 1.6 kb is present in embryos and L1, L2 and L3 larvae. pag-3 message levels were about twofold higher in pag-3 mutants than in wild-type animals, which suggested that pag-3 may negatively regulate its own expression. pag-3lacZ fusion genes were expressed in the BDU interneurons, the touch neurons, 11 VA and 11 VB ventral cord motor neurons, two AVF interneurons and in unidentified neurons of the retrovesicular ganglion. The BDU neurons and the ALM touch neurons are lineal sister cells in the AB.a lineage and the VA and VB motor neurons are lineal sister cells in the AB.p lineage. The VA motor neurons are required for backward movement and the VB motor neurons are required for forward movement. Mosaic analysis showed that the wild-type pag-3 gene is required in the AB.p lineage for coordinated movement and in the AB.a lineage to suppress touch neuron gene expression in the BDU neurons. Because pag-3 is expressed in both the BDU neurons and in the touch neurons, another protein(s) not expressed in the touch neurons may interact with pag-3 to repress touch neuron gene expression in the BDU neurons. Alternatively, another protein in the touch receptor cells may inactivate PAG-3 and allow expression of the touch receptor program. These results show that pag-3 is a temporally regulated gene that is expressed early in development and functions in multiple types of neurons. They also strongly suggest that the PAG3 protein is a DNA-binding protein with properties similar to the mammalian proto-oncogene product GFI-1.

Kinetic mechanism of transcription initiation by bacteriophage T7 RNA polymerase

The kinetic mechanism of transcription initiation by bacteriophage T7 RNA polymerase was investigated using transient state kinetic methods. Transcription by bacteriophage T7 RNA polymerase occurs in three stages consisting of initiation, promoter clearance, and elongation. Abortive products, up to 6-8-mer, were synthesized during the initiation phase; the transition from initiation to elongation occurred between the synthesis of 6-8-mer and 11-12-mer, and the processive elongation phase began after the synthesis of 12-mer RNA. Our results show that the synthesis of elongation product from the phi 10 promoter is limited both by the efficiency of initiation and by the frequency at which the polymerase escapes the promoter. Studies with heparin trap suggest that the polymerase maintains contact with the promoter region during multiple turnovers of abortive RNA synthesis; thus, the polymerase does not completely dissociate from the promoter after each event of abortive RNA synthesis. The pre-steady-state kinetics of RNA synthesis indicate that initiation occurs at a rate constant (3.5 s(-1)) that is about 30 times faster than the steady-state rate constant of RNA synthesis (0.1 s(-1)). The steady-state rate constant of RNA synthesis is limited largely by the cycling of the RNA polymerase, whereas initiation is limited by the formation of pppGpG, the first RNA product. We show that the synthesis of pppGpG is not limited by steps associated with GTP binding, DNA binding, or the melting of the promoter DNA. Instead, the kinetic results indicate that initiation at the phi10 promoter is limited either by the first phosphodiester bond formation step or more likely by a conformational change prior to pppGpG formation. Such a conformational change could play a role in proper alignment of the initiating and elongating NTPs for efficient phosphodiester bond formation and in maintaining the fidelity of RNA synthesis.