Dissection of protein-carbohydrate interactions in mutant hen egg-white lysozyme complexes and their hydrolytic activity

Trp62 in the binding subsite B of hen egg-white lysozyme shows general features often observed in protein-carbohydrate interactions including a stacking interaction and a hydrogen bonding network with water molecules. A previous report by our group showed that the perturbation of these interactions by substitution of Trp62 with tyrosine or phenylalanine affects the substrate binding modes and also enhances the hydrolytic activity. In order to elucidate the relationship between structural and functional changes of these protein-carbohydrate interactions, the Trp62Tyr and Trp62Phe mutants complexed with the substrate analogue, (GlcNAc)3, were analyzed at 1.8 A resolution by X-ray crystallography. The overall structures of the mutant enzymes are indistinguishable from that of the wild type enzyme. Although the wild-type enzyme binds (GlcNAc)3 in only one binding mode (A-B-C), the Trp62Tyr mutant binds (GlcNAc)3 in two binding modes (A-B-C, B-C-D) and the Trp62Phe mutant has an even weaker binding mode. The aromatic rings of Tyr62 and Phe62 maintain their interactions with the carbohydrate molecules, but make fewer stacking interactions with the GlcNAc in the B site than the wild-type enzyme does. The hydroxyl group of Tyr62 interacts weakly with a water molecule which mediates hydrogen bonding in the GlcNAc residues in the B and C sites. The C-6 hydroxyl group of the GlcNAc residue in the C site rotates around the C-5-C-6 bond to complete the hydrogen bond network in the Trp62Tyr mutant-(GlcNAc)3 complex. On the other hand, this hydrogen bonding network does not form in the Trp62Phe mutant-(GlcNAc)3. In addition to these structural studies, the kinetic parameters of the hydrolysis of 4-methylumbelliferyl N-acetyl-chitotriose, ((GlcNAc)3-MeU), have been determined in order to further characterize the enzymatic properties of these mutant lysozymes. This demonstrates that the modulation of the hydrogen bonding network, including the flexible part of the carbohydrate and water molecules and/or the slight reduction of stacking interaction in the B site, alters the binding mode toward the carbohydrate and induces an enhancement of the hydrolytic activity.

Structure of a conformationally constrained Arg-Gly-Asp sequence inserted into human lysozyme

To examine the effect of a conformational constraint introduced into the Arg-Gly-Asp (RGD) sequence on cell adhesion activity, we constructed a mutant protein by inserting an RGD-containing sequence flanked by two Cys residues between Val74 and Asn75 of human lysozyme. The CRGDSC-inserted lysozyme was expressed in yeast, purified, and designated as Cys-RGD4. Using baby hamster kidney cells, Cys-RGD4 was shown to possess even higher cell adhesion activity than that of the RGDS-inserted lysozyme, RGD4. The Cys-RGD4 protein was co-crystallized with a lysozyme inhibitor, tri-N-acetylchitotriose, and the three-dimensional structure was determined at 1.6-A resolution by x-ray crystallography. In contrast to RGD4, the inserted RGD-containing region of Cys-RGD4 was well defined. The structural analysis revealed that the two inserted Cys residues form a new disulfide bond in Cys-RGD4, as expected, and that the RGD region assumes a type II' beta-turn conformation of Gly-Asp with a hydrogen bond between the C = O of Arg and the H-N of Ser. In addition, it was confirmed that two more hydrogen bonds are present in the RGD region of the Cys-RGD4 lysozyme. These results suggest that the conformation of the RGD-containing region is rigid and stable in the Cys-RGD4 molecule and that the type II' beta-turn structure of RGD is essential for binding to integrins with high affinity.

Repetitive, low-dose tissue plasminogen activator for clearance of experimental vitreous hemorrhage

PURPOSE

To investigate the effectiveness of repetitive, low-dose tPA for clearance of experimental vitreous hemorrhage.

METHODS

The model vitreous hemorrhage was produced by intravitreal injection of 0.05ml of autologous citrated whole blood in 14 rabbits (28 eyes). One week after the creation of vitreous hemorrhage, the eyes were randomly separated into 3 groups. Groups 1 and 2 received two injections of 5 or 25 micrograms of tPA, respectively, with one injection in a 7-day interval. Group 3 received two injections of PS in the same way.

RESULTS

The clearance of vitreous hemorrhage in tPA-treated groups was significantly faster than that in the control group (P < 0.05, or P < 0.01). However, there was no statistically significant difference between the two tPA-treated groups. Not any retinal toxicity was detected by ERG, light microscopy, and transmission electron microscopy examinations.

CONCLUSIONS

Repetitive injections of low-dose tPA were effective in the treatment of experimental vitreous hemorrhage. Whether it is effective on the clearance of vitreous hemorrhage in human eyes needs further investigation.

[Pathological study of hepatoid gastric adenocarcinomas]

Routine examination of pathologic sections in 500 cases of primary gastric adenocarcinomas was carried out by light microscopy. Regions of hepatocellular carcinomatoid differentiation were discovered in 12 of the 500 cases. In 11 of them, histopathologic features were described in great detail and the hepatocellular carcinomatoid regions were studied by four kinds of immunohistochemistrical methods. The results indicate that positive staining for AFP was seen in 9 cases but negative in 9 controls, weakly positive for CEA in 10 cases, but strongly positive in 8 controls. Staining for alpha 1-AT and alpha 1-ACT showed no differences as compared to controls. The clinical pathological features and its relationship with AFP are discussed. It is suggested that hepatoid gastric adenocarcinoma is a subtype of gastric adenocarcinoma.

[Personal characteristics as risk factors of endometriosis]

203 patients with pelvic endometriosis, all Beijing resident, were collected from the Peking Union Medical College Hospital and the Beijing Obstetrical and Gynecological Hospital. The diagnosis of endometriosis was confirmed by pathological examination of surgical specimens in 186 patients and by aspiration of chocolate substance under laparoscopy in 17. Two population controls, age matched +/- 1 year, were randomly selected for each patient from the same residential area, after careful pelvic examinations and ultrasonographies. A questionnaire for any possible risk factors to endometriosis was developed and with this questionnaire a face to face interview for each subject was carried out by the trained interviewers. All interviews were tape recorded and calculated in a AST 386 computer. The continuous logistic regression for matched sites was used to obtain a maximum likelihood point and to control the potential confounding effects of selected variables. Relative risk (RR) substituted for odds ratio together with the 95% confidence intervals was estimated. All the results were adjusted for the variables of the model including some relevant factors of menstruation, pregnancy and contraception. An increased risk for endometriosis was found to be related to women who had a higher level of education. Even it was adjusted for age of first marriage and pregnancy, gravidity, parity, contraception and all other variables of the model, the relative risk was 1.84 for endometriosis. Therefore, it is the education level itself that plays a true role in development of endometriosis. Although there was a trend in risk for endometriosis in height, it was statistically insignificant.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural changes of active site cleft and different saccharide binding modes in human lysozyme co-crystallized with hexa-N-acetyl-chitohexaose at pH 4.0

Human lysozyme was co-crystallized with hexa-N-acetyl-chitohexaose, (GlcNAc)6, at pH 4.0 and 4.0 degrees C in a new orthorhombic form, where two protein molecules, MOL1 and MOL2, were contained in an asymmetric unit. The three-dimensional structure was refined to an R-factor of 17.0% at 1.6 A resolution. It was found that (GlcNAc)6 had already been cleaved to (GlcNAc)4 and (GlcNAc)2. In MOL1, (GlcNAc)4 was bound to the A, B, C, and D subsites, and binding sites of (GlcNAc)2 were close to the E and F subsites proposed on the basis of model building by Phillips and his colleagues. In MOL2, only the (GlcNAc)4 moiety could be found in the A, B, C and D subsites. Significant shifts of the backbone atoms were observed in the region of residues 102 to 120, which composed one side of the wall of the active site cleft. Consequently, the active cleft, with respect to the saccharide binding sites A, B and C, is narrower in both protein molecules. The residues 109 to 111 in site D of MOL1 are moved toward saccharide residue D, whereas those of MOL2 are only slightly shifted. In spite of these facts, the saccharide residues in site MOL1 and MOL2 are moved inside of the cleft. The distribution of water molecules and the hydrogen bond network in site D differ between the structures of MOL1 and MOL2. These structural changes in the active site cleft may be responsible for accommodating the substrate and releasing the products of hydrolysis. These results suggest that the three-dimensional structures of MOL1 and MOL2 remain in intermediate states between a transition state and an enzyme/product complex state.

Novel regulation of pyruvate dehydrogenase phosphatase purified from anaerobic muscle mitochondria of the adult parasitic nematode, Ascaris suum

Pyruvate dehydrogenase (PDHb) phosphatase has been purified to apparent homogeneity from mitochondria of the adult parasitic nematode, Ascaris suum. The enzyme is a heterodimer of 89 and 50 kDa, as judged by SDS-polyacrylamide gel electrophoresis. It appeared to copurify with its substrate, pyruvate dehydrogenase (E1) and could be separated by chromatography on Superose 12 in the presence of 0.5 M NaCl. Phosphatase activity was absolutely dependent on Mg2+, with an apparent Km of about 4 mM. In contrast to PDHb phosphatases from other sources, the ascarid enzyme was not stimulated by Ca2+ or spermine, but it was stimulated by L-malate, the major mitochondrial substrate in A. suum. L-Malate had no effect on the dephosphorylation of isolated [32P]E1, but it decreased the apparent Km of the phosphatase for 32P-pyruvate dehydrogenase complex or [32P]E1 in the reconstituted complex about 4-6-fold, suggesting that the dihydrolipoyl transacetylase (E2) core was necessary for malate activation. The activity of the pyruvate dehydrogenase complex (PDC) in isolated A. suum muscle mitochondria was significantly greater than that reported for other mitochondria, and the majority of the PDC appeared to be in the phosphorylated inactive state. Incubation of intact phosphorylating A. suum muscle mitochondria in the absence of substrate and the presence of an uncoupler did not lead to an activation of PDC activity. In contrast, incubation in malate plus Mg2+ markedly increased PDC activity. These results contrast markedly with those reported for aerobic mitochondria and suggest that the regulation of PDC activity in these anaerobic organelles differs significantly from that of their mammalian hosts.

Implementation of the chemical reaction interface mass spectrometry technique on a Hewlett-Packard mass-selective detector

A microwave-powered chemical reaction interface has been installed in a Hewlett-Packard gas chromatograph-mass spectrometer (GC-MS) system (5890 IT gas chromatograph-S971 mass-selective detector). The technical details and optimization strategies are discussed. The evaluation of this new setup is presented, showing detection limits of 1 ng of (13)C-, (15)N-, and Cl-containing compounds with signal-to-noise ratios greater than or egual to 3. Selective detection was evaluated with a urine sample from a dog dosed with (15)N3-midazolam that had been previously analyzed by using a differentially pumped research-level quadrupole mass spectrometer. The results show that the detection of (15)N and Cl remains highly selective and the mass-selective detector gives comparable sensitivity to the larger instrument when the latter is operating over a conventional mass range. The capability for chemical reaction interface mass spectrometry can be easily accomplished with an inexpensive GC-MS system.

[Using ELISA to evaluate the serologic and epidemiologic effect following rabies vaccination]

After vaccinating the people bitten by animals against rabies, we have examined their serum antibodies by using ELISA. One year later, we sent a mail to everyone of them inquiring if he had contracted rabies. The response rate was 85%. The case fatality rate of the positive antibody group was 0.24% (1/415). The case fatality rate of the negative antibody group was 3.16 (3/95). It showed that there was significant difference in the case fatality rate of rabies between the two groups, (P = 0.022). The dead person of the positive antibody group was bitten on his cheek by a rabid dog. He had not cleaned his wound. He had received 6 injections of rabies vaccines. His incubation period was 28 days. The P/N of serum antibody on the 28th day was 3.27.

Lecompte procedure for complete transposition of the great arteries with ventricular septal defect and pulmonary stenosis

From December 1988 to February 1993, 19 patients were treated by the Lecompte procedure for complete transposition of the great arteries associated with a ventricular septal defect and pulmonary stenosis. The mean age at operation was 3.1 +/- 0.8 years (mean +/- standard error). This technique consisted of resecting the outlet septum, constructing a tunnel that connected the left ventricle to the aorta, closing the proximal pulmonary arterial stump, pulling the distal pulmonary artery down to the right ventriculotomy site directly, and covering anteriorly with the fixed autologous pericardium. Operative mortality was 5.3%. The mean follow-up was 24.2 +/- 3 months, with no late death. One reoperation was performed because of residual right ventricular outflow tract obstruction. All survivors were studied by echocardiography at intervals of 6 months to 1 year. In all survivors (except for 1 child who underwent reoperation), the estimated pressure gradient between the right ventricle and the pulmonary artery, the structure of the left ventricular outflow tract, left ventricular function, and right ventricular contractility were all satisfactory.

Preparation, characterization and application of monoclonal antibodies against PAI-1

Six hybridoma cell lines (AP1-AP6) secreting monoclonal antibodies (McAb) against PAI-1 were obtained by fusing the murine myeloma cell line SP2/0 with the spleen cells from Balb/c mouse immunized with recombinant PAI-1 expressed in E. coli. These antibodies were purified by SPA affinity chromatography. All McAbs recognized rPAI-1 and PAI-1 from the human hepatoma cell line HepG2. The titers of ascites were more than 10(6). The antibody-antigen affinity constants (Kaff) for anti-PAI-1 McAb measured by EIA were between 3.45 x 10(7)-1.05 x 10(10) M. AP2 and AP3 McAbs were effective in quenching the activity of PAI-1. Partial quenching of PAI-1 activity was achieved with AP4, AP5 and AP6 McAbs respectively. AP1 McAb had no effect upon PAI-1 activity. Three of the six McAbs (AP1, AP4 and AP5) bound to the PAI-1/t-PA complex, while the others did not. The PAI-1 was purified 51 folds to homogeneity from serum free medium of HepG2 with the recovery rate of 92% by one-step procedure using Sepharose 4B conjugated with anti-PAI-1 McAb (AP1, AP3 and AP4). A sandwich ELISA for the measurement of PAI-1 antigen in human plasma was developed, based on anti-PAI-1 McAb against non-overlapping epitopes. The mean value of plasma PAI-1 for the healthy donors was 24.7 +/- 7.75 ng/ml measured by ELISA.

Neuro-pathophysio-biochemical profiles of neonatal asphyxia

Neurological and neuroelectrophysio-biochemical profiles were evaluated in newborn lambs exposed to severe temporary asphyxia. Isoelectric EEG, marked disturbances of phosphorus magnetic resonance spectrum (31P-MRS), and significant brain intracellular acidosis (pHi) were noted during asphyxia. Following resuscitation, the presence of early postasphyxic blood-brain-barrier (BBB) opening was associated with a marked transient increase in intracranial pressure (ICP), a 50% neonatal mortality and a 67% incidence of severe asphyxic encephalopathy. In contrast, those lambs exposed to the same magnitude of asphyxia, but without early BBB opening experienced neither death nor severe neurological deficits. Further, these lambs showed a rapid progressive normalization of the 31P-MRS and pHi, despite, the lack of EEG recovery in the first hour following resuscitation. Thus, the present study depicts that the early postasphyxic BBB disruption following temporary neonatal asphyxia is associated with poor prognosis.

Rezoning and Dynamic Substructuring Techniques in FEM Simulations of Welding Processes

Distortion and residual stresses cause significant problems in the welding of large structures. Prediction of these phenomena would provide substantial assistance to the design and fabrication of welding. Unfortunately, the complexity of structural interactions during welding and the severe nonlinearities associated with the welding process limit the application of weld simulations. This presentation develops rezoning and dynamic substructuring techniques that make the finite element welding simulation of large structures more tractable. Both techniques exploit the fact that only a local zone around the welding electrode is nonlinear during welding. We therefore model the local nonlinear zone around the electrode or heat source with a dense finite element mesh. The rest of the larger structure is modeled using both a coarser mesh and substructures. The model is then redefined incrementally to represent the motion of the electrode through the larger structure. The redefinition is performed on the deformed geometry of the previous increment, achieving a step-wise coupled thermo-mechanical analysis. The techniques are applied to a two-dimensional plate welding example, achieving significant reductions in model size. Computer memory requirements and analysis times achieve close to order-of-magnitude reductions. Three-dimensional welding simulations should experience greater reductions in analysis time. Although developed for welding applications, the rezoning and dynamic substructuring techniques can also be used for other analyses involving a small nonlinear zone translating within a larger elastic body.

Evidence for sensing and integration of biological signals by the capillary network

The aim of this study was to explore the phenomenon first described by Dietrich (Microvasc. Res. 38: 125-135, 1989) in which a local application of norepinephrine (NE) on a capillary can temporarily reduce flow via constriction of the feeding arteriole. Our objectives were to show that this phenomenon of remote response is not limited to vasoconstriction, can be elicited by materials other than NE, shows stimulus-strength dependency, and can be integrated within the capillary network. We used an intravital micropharmacological approach to iontophoretically apply (in mM concentrations in the pipette) NE, acetylcholine (ACh), 5'-N-ethylcarboxamidoadenosine (NECA, adenosine analogue), K+, and H+ on capillaries of the frog sartorius muscle in situ. Responses were measured in terms of changes in velocity of red blood cells (VRBC) in capillaries or in terms of changes in arteriolar diameter. ACh (3 mM) caused significant increases in diameter (from 34 to 37 microns) and in VRBC (from 250 to 340 microns/s, i.e., 36%). NE (3 mM) reduced VRBC by 16%. The magnitude of ACh and NE velocity responses increased with increasing pipette concentration and with increasing iontophoretic current. The ACh response was blocked by a local pretreatment with atropine. NECA, K+, and H+ caused 20-40% increases in VRBC. Dual application of NE on two capillaries fed by the same arteriole resulted in a greater VRBC reduction than for single NE application. Dual application of NE and ACh significantly attenuated the ACh response.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicological investigations on silicon carbide. 1. Inhalation studies

The question of lung damage as a result of exposure to silicon carbide (SiC) was investigated by inhalation experiments to obtain information on the qualitative response of lung tissue to the test substance (SiC). For comparison, quartz, kaolinite, and tempered clay dusts were used. The indices for the effects of the dusts studied were organ weights, numbers of bronchoalveolar cells, lung surfactant phospholipid concentrations including subfractions, and lung clearance. Exposure to the test samples was carried out according to the Essen inhalation model in two independent series. The results of the two series were similar: Compared with sham controls, exposure to SiC did not affect the indices studied. Even at a low dose (a quarter of the SiC dose) quartz gave pronounced deviations in all indices. In particular, an increase in granulocytes indicated toxic properties of the dust. The long term elimination of quartz from the lung was worse than that of SiC. The kaolinite and tempered clay dusts were intermediate between SiC and quartz based on several of the indices studied. It is concluded that SiC is deposited practically inert in the lung.

Drug metabolism studies using "intrinsic" and "extrinsic" labels. A demonstration using 15N vs. Cl in midazolam

The chemical reaction interface for mass spectrometry (CRIMS) has been used to evaluate the ability of an "intrinsic" label (chlorine) to replace an "extrinsic" label (15N) in a study of the metabolite profile of a drug, in this case the benzodiazepine anesthetic agent midazolam. We find equally high selectivity and comparable signal/noise characteristics for chlorine as for isotopic nitrogen demonstrating that the chlorine in midazolam is itself an effective label and that special synthesis to incorporate isotopic labels is not necessary. The power of either detection mode of CRIMS is shown by detecting 14 metabolites, whereas only four had been previously determined. The ratios of 15N/Cl for each metabolite peak along with conventional mass spectra provide clues to the structures of these new metabolites.

Selective detection of chlorine-containing compounds by gas chromatography/chemical reaction interface mass spectrometry

Chemical reaction interface mass spectrometry (CRIMS) was studied as a gas chromatographic detection technique for chlorine-containing compounds. Both SO2 and HBr were tested as reactant gases. With SO2, a detection limit of 50 pg of diazepam and a linear range of 4 orders of magnitude were achieved, and the experimental data were reproducible. With HBr, the detection limit was 10 ng of diazepam and the linear dynamic range was only 2 orders of magnitude. The possible pharmacological application of CRIMS was studied using urine spiked with diazepam and several of its metabolites, and the results show CRIMS to be a simple but potentially powerful method in drug metabolism studies.

Finite Element Simulation of Welding of Large Structures

Current simulations of welding distortion and residual stress have considered only the local weld zone. A large elastic structure surrounding a weld, however, can couple with the welding operation to produce a final weld state much different from that resulting when a smaller structure is welded. The effect of this coupling between structure and weld has the potential of dominating the final weld distortion and residual stress state. This paper employs both two-and three-dimensional finite element models of a circular cylinder and stiffening ring structure to investigate the interaction of a large structure on weld parameters such as weld gap clearance (fitup) and fixturing. The finite element simulation considers the full thermo-mechanical problem, uncoupling the thermal from the mechanical analysis. The thermal analysis uses temperature-dependent material properties, including latent heat and nonlinear heat convection and radiation boundary conditions. The mechanical analysis uses a thermal-elastic-plastic constitutive model and an element “birth” procedure to simulate the deposition of weld material. The effect of variations of weld gap clearance, fixture positions, and fixture types on residual stress states and distortion are examined. The results of these analyses indicate that this coupling effect with the surrounding structure should be included in numerical simulations of welding processes, and that full three-dimensional models are essential in predicting welding distortion. Elastic coupling with the surrounding structure, weld fitup, and fixturing are found to control residual stresses, creating substantial variations in highest principal and hydrostatic stresses in the weld region. The position and type of fixture are shown to be primary determinants of weld distortion.

The pyruvate dehydrogenase complex from the parasitic nematode Ascaris suum: novel subunit composition and domain structure of the dihydrolipoyl transacetylase component

The pyruvate dehydrogenase complex (PDC) from muscle of the adult parasitic nematode Ascaris suum plays a unique role in its anaerobic mitochondrial metabolism. Resolution of the intact complex in high salt dissociates the pyruvate dehydrogenase subunit but leaves the dihydrolipoyl dehydrogenase subunit (E3) and two other proteins with apparent M(r)s of 45 and 43 kDa bound to the dihydrolipoyl transacetylase (E2) core. These proteins are not observable on Coomassie brilliant blue-stained gels of other eukaryotic PDCs, but the 45-kDa protein is similar in apparent M(r), pI, and sensitivity to trypsin to the Kb subunit of the bovine kidney PDH alpha kinase. Acetylation of the ascarid PDC with [2-14C]pyruvate under conditions designed to maximize the incorporation of label into protein yielded only a single radiolabeled subunit, E2. These results confirm earlier reports that the ascarid PDC lacks protein X, an integral component recently identified in other eukaryotic PDCs. About 1.6 to 1.8 mol of 14C was incorporated/mole of E2, suggesting that the ascarid E2 contained two lipoly-bearing domains. Domain mapping of the 14C-acetylated ascarid E2 by limited tryptic digestion identified two lipoyl-bearing fragments with apparent M(r)s of 50 and 34 kDa and two core fragments with apparent M(r)s of 46 and 30 kDa. The ascarid E2 domain structure appears to be similar to that of other E2s. However, it appears that the subunit-binding domain (E2B) of the ascarid E2 may be significantly larger or be flanked by larger than normal interdomain regions. An enlarged E2B domain may be necessary to accommodate the additional binding of E3 to the E2 subunit in the ascarid complex, in the absence of protein X.

[Effect of concentration of nutrients solution on the growth of Salvia miltiorrhiza Bge]

The experiment on the effect of various concentrations of nutrient solution on sand culture of Salvia miltiorrhiza was carried out. The results show that Salvia miltiorrhiza is a fertilizer tolerant plant. It can grow well and give high yield when the total concentration of nutrient reaches 0.37%.