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Biomedical subjects

E Zhang

Publications and source records attributed to E Zhang.

At least 37 records · Page 2Linked to original sources
PubMed1999

Structure of extracellular tissue factor complexed with factor VIIa inhibited with a BPTI mutant.

The event that initiates the extrinsic pathway of blood coagulation is the association of coagulation factor VIIa (VIIa) with its cell-bound receptor, tissue factor (TF), exposed to blood circulation following tissue injury and/or vascular damage. The natural inhibitor of the TF.VIIa complex is the first Kunitz domain of tissue factor pathway inhibitor (TFPI-K1). The structure of TF. VIIa reversibly inhibited with a potent (Ki=0.4 nM) bovine pancreatic trypsin inhibitor (BPTI) mutant (5L15), a homolog of TFPI-K1, has been determined at 2.1 A resolution. When bound to TF, the four domain VIIa molecule assumes an extended conformation with its light chain wrapping around the framework of the two domain TF cofactor. The 5L15 inhibitor associates with the active site of VIIa similar to trypsin-bound BPTI, but makes several unique interactions near the perimeter of the site that are not observed in the latter. Most of the interactions are polar and involve mutated positions of 5L15. Of the eight rationally engineered mutations distinguishing 5L15 from BPTI, seven are involved in productive interactions stabilizing the enzyme-inhibitor association with four contributing contacts unique to the VIIa.5L15 complex. Two additional unique interactions are due to distinguishing residues in the VIIa sequence: a salt bridge between Arg20 of 5L15 and Asp60 of an insertion loop of VIIa, and a hydrogen bond between Tyr34O of the inhibitor and Lys192NZ of the enzyme. These interactions were used further to model binding of TFPI-K1 to VIIa and TFPI-K2 to factor Xa, the principal activation product of TF.VIIa. The structure of the ternary protein complex identifies the determinants important for binding within and near the active site of VIIa, and provides cogent information for addressing the manner in which substrates of VIIa are bound and hydrolyzed in blood coagulation. It should also provide guidance in structure-aided drug design for the discovery of potent and selective small molecule VIIa inhibitors.

Amino Acid Chloromethyl Ketones↗
PubMed1999

Human immunodeficiency virus type 1 subtypes differ in disease progression.

At least 10 different genetic human immunodeficiency virus type 1 (HIV-1) subtypes (A-J) are responsible for the AIDS pandemic. Much of the understanding of HIV-1 disease progression derives from studies in the developed world where HIV infection is almost exclusively subtype B. This has led many to question whether the properties and consequences of HIV-1 infection can be generalized across subtypes that afflict the majority of infected persons in the developing world. From 1985 to 1997, a prospective study of registered female sex workers in Senegal tracked the introduction and spread of HIV-1 subtypes A, C, D, and G. In clinical follow-up, the AIDS-free survival curves differed by HIV-1 subtype. Women infected with a non-A subtype were 8 times more likely to develop AIDS than were those infected with subtype A (hazard ratio=8.23; P=. 009), the predominant subtype in the study. These data suggest that HIV-1 subtypes may differ in rates of progression to AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1999

[A study on inhibitory effect of plant growth retardants on earlier bolting of Chinese Angelica].

OBJECTIVE: Seeking chemical ways of controlling the earlier bolting of Chinese Angelica (CA). METHOD: PP333, B9 and MH in different concentrations and combinations were sprayed into the CA leaves in different periods. RESULTS: In leaf proliferating period the spray could inkibit the earlier bolting, shortening the length of the stem foot, increasing the stem diameter and enhancing the leaf chlorophy 11 contents. The quality of CA production was increased as a result of greater root weight and main root volume. In leaf luxuriatino period the spray showed no marked effect. The growth of the plant would be inhibited by any spray in excessive concentrations. CONCLUSION: Leaf spray could control the earlier bolting of CA.

Angelica sinensis↗
PubMed1999

[Study of bacterial adhesion to prosthetic valve materials in vitro].

This article reports a study of the bacterial adhesion to prosthetic valve materials in vitro. The method for assessing the degree of bacterial adhesion to prosthetic valve materials was established primarily. The capacities of staphylococcus aureus(SA), staphylococcus epidermidis(SE), Escherichia Coli(EC) and Pseudomonas aeruginosa(PA) for adhesion to Dacron, Pyrolytic carbon and polytetrofluoroethylene (PTFE) were quantitatively determined by the plate counting and Gamma-ray counting of 125I radiolabeled bacteria in vitro. The results showed that the capacities of four types of bacteria for adhesion to Dacron, Pyrolytic carbon and PTFE coincided with the bacterial-growth curve. The capacities of four bacteria for adhering to Dacron were stronger. The adhesion of SE to Pyrolytic carbon was the strongest. The adhesion of PA Kept up a high level. The capacities of EC and PA for adhering to PTFE were the strongest. The results indicate that the capacities of different types of bacteria for adhesion to the same prosthetic valve material are different, and the capacities of one type of bacteria for adhesion to different materials are also different.

Bacterial Adhesion↗
PubMed1999

[Modification of the surface of prosthetic valve material by LGDP for protection against microbial adhesion].

This study aimed at the surface modification of prosthetic valve materials by means of cold glow discharge plasma. Orthogonal design was adopted to select the optimal scheme by the experiments of the singular factor, such as output power, gas flow rate, treatment time etc. The PEG-200 was introducted to the surface. Grafting a layer of heparin onto the surface; coating a layer of PEG-like onto the surface first, and then the grafting heparin. Comparing the adhesive amounts of staphylococcus epidermidis (SE), the adhesive curves for Dacron, which was treated by the above methods; the last one is the best.

Bacterial Adhesion↗
PubMed1999

[Studies on the feasibility of detecting circulating antibodies in saliva of Schistosoma japonicum infected rabbits].

AIM: To investigate the feasibility of detecting anti-Schistosoma japonicum antibodies in saliva. METHODS: Saliva and serum samples of 5 infected, 7 reinfected and 8 treated rabbits were collected at different times periods. The CAb in saliva and serum was detected by using ELISA. RESULTS: The sensitivity of ELISA was 94.7% for saliva and 100% for serum. The specificity of ELISA was 100% for both saliva and serum. CONCLUSION: Saliva can be used to detect circulating antibodies for the diagnosis of schistosomiasis japonica.

Animals↗
PubMed1999

[Determination of circulating antigen in urine of rabbits infected with Schistosoma japonicum].

AIM: To develop an immunoassay for the detection of circulating schistosome antigen (CSA) in host urine. METHODS: CSA extracted from the urine of the rabbits infected with Schistosoma japonicum was used for preparing and selecting specific monoclonal antibody. A one-step dot-ELISA using this specific McAb and a 2nd antibody was used for detection of circulating schistosome antigen in the urine of infected rabbits. RESULTS: No CSA was detected in urine from all of 22 rabbits before infection. The positive rate of CSA in infected rabbits was correlated with the intensity of infection and the time of infection. No CSA was detected in the urine rabbits of 3 weeks after infection with 25 cercariae while the positive rate of CSA in the urine from rabbits infected with 200 cercariae was 40% and 100% after 3 and 6 weeks, respectively. A combination of CSA detection in both urine and serum may increase the detectability. CONCLUSION: The specific McAb prepared by urine CSA of Schistosoma japonicum-infected rabbits can be used as a probe for detecting CSA in the urine of infected rabbits.

Animals↗
PubMed1998

Highly selective mechanism-based thrombin inhibitors: structures of thrombin and trypsin inhibited with rigid peptidyl aldehydes.

The crystal structures of three highly potent and selective low-molecular weight rigid peptidyl aldehyde inhibitors complexed with thrombin have been determined and refined to R values 0.152-0. 170 at 1.8-2.1 A resolution. Since the selectivity of two of the inhibitors was >1600 with respect to trypsin, the structures of trypsin-inhibited complexes of these inhibitors were also determined (R = 0.142-0.157 at 1.9-2.1 A resolution). The selectivity appears to reside in the inability of a benzenesulfonamide group to bind at the equivalent of the D-enantiomorphic S3 site of thrombin, which may be related to the lack of a 60-insertion loop in trypsin. All the inhibitors have a novel lactam moiety at the P3 position, while the two with greatest trypsin selectivity have a guanidinopiperidyl group at the P1 position that binds in the S1 specificity site. Differences in the binding constants of these inhibitors are correlated with their interactions with thrombin and trypsin. The kinetics of inhibition vary from slow to fast with thrombin and are fast in all cases with trypsin. The kinetics are examined in terms of the slow formation of a stable transition-state complex in a two-step mechanism. The structures of both thrombin and trypsin complexes show similar well-defined transition states in the S1 site and at the electrophilic carbon atom and Ser195OG. The trypsin structures, however, suggest that the first step in a two-step kinetic mechanism may involve formation of a weak transition-state complex, rather than binding dominated by the P2-P4 positions.

Aldehydes↗
PubMed1998

[A preliminary investigation on causes of failure of vitreoretinal surgery for complicated rhegmatogenic retinal detachments].

OBJECTIVE: To evaluate the failure causes of vitreoretinal surgery for complicated rhegmatogenic retinal detachment. METHODS: Vitreoretinal (VR) surgery was performed on 477 cases (479 eyes) with complicated rhegmatogenic retinal detachment, the operative procedures including vitrectomy, peeling of pre-retinal membrane, fluid-air exchange, inert gas (SF(6) or C(3)F(8)) or silicone tamponade. RESULTS: On discharge, the operation was effective in 349 eyes (72.87%) and failed in 130 (27.13%) eyes. CONCLUSION: The multiple stepwise multivariate regression shows that the factors significantly influencing VR surgery are silicone tamponade, giant retinal tears, SF(6) tamponade, iatrogenic tear, anterior proliferative vitreoretinopathy (PVR), subretinal proliferation, PVR, C(3)F(8) tamponade, operative frequency and choroidal detachments.

Adolescent↗
PubMed1998

[Application of dot immunogold filtration assay for diagnosis of Schistosomiasis japonica].

AIM: To quest for a simple and convenient assay for the diagnosis of schistosomiasis. METHODS: Three monoclonal antibodies against different epitopes of antigens of S. japonicum were used to develop a dot immunogold filtration assay for detection of schistosomal antigen-antibody reaction on the membrane during the filtration process. The results could be read with the naked eye within a few minutes. RESULTS: The sensitivity of the SEA assay was 16 ng/ml. In 69 serum samples from patients with chronic schistosomiasis, the positive rate and specificity of this assay were 60.8% and 95.2%, respectively. Dot-ELISA was used in detecting 137 serum samples from patients with chronic schistosomiasis, the positive rate and specificity were 54.7% and 94.6%, respectively. When sandwich-ELISA was used in detecting 118 serum samples from patients with chronic schistosomiasis, the positive rate and specificity were 61.9% and 95.7%, respectively. CONCLUSION: The sensitivity and specificity of DIFA were similar to those of ELISA, but DIFA required less time and no special equipment.

Enzyme-Linked Immunosorbent Assay↗
PubMed1997

Mechanism of enolase: the crystal structure of asymmetric dimer enolase-2-phospho-D-glycerate/enolase-phosphoenolpyruvate at 2.0 A resolution.

Enolase, a glycolytic enzyme that catalyzes the dehydration of 2-phospho-d-glycerate (PGA) to form phosphoenolpyruvate (PEP), is a homodimer in all eukaryotes and many prokaryotes. Here, we report the crystal structure of a complex between yeast enolase and an equilibrium mixture of PGA and PEP. The structure has been refined using 29 854 reflections with an F/sigma(F) of >/=3 to an R of 0.137 with average deviations of bond lengths and bond angles from ideal values of 0.013 A and 3.1 degrees , respectively. In this structure, the dimer constitutes the crystallographic asymmetric unit. The two subunits are similar, and their superposition gives a rms distance between Calpha atoms of 0.91 A. The exceptions to this are the catalytic loop Val153-Phe169 where the atomic positions in the two subunits differ by up to 4 A and the loop Ser250-Gln277, which follows the catalytic loop Val153-Phe169. In the first subunit, the imidazole side chain of His159 is in contact with the phosphate group of the substrate/product molecule; in the other it is separated by water molecules. A series of hydrogen bonds leading to a neighboring enolase dimer can be identified as being responsible for ordering and stabilization of the conformationally different subunits in the crystal lattice. The electron density present in the active site suggests that in the active site with the direct ligand-His159 hydrogen bond PGA is predominantly bound while in the active site where water molecules separate His159 from the ligand the binding of PEP dominates. The structure indicates that the water molecule hydrating carbon-3 of PEP in the PEP --> PGA reaction is activated by the carboxylates of Glu168 and Glu211. The crystals are unique because they have resolved two intermediates on the opposite sides of the transition state.

Crystallization↗
PubMed1997

The molecular environment of the Na+ binding site of thrombin.

When Na+ binds to thrombin, a conformational change is induced that renders the enzyme kinetically faster and more specific in the activation of fibrinogen. Two Na+ binding sites have here been identified crystallographically by exchanging Na+ with Rb+. One is intermolecular, found on the surface between two symmetry-related thrombin molecules. Since it is not present in thrombin crystal structures having different crystal systems, the other Na+ site is the functionally relevant one. The second site has octahedral coordination with the carbonyl oxygen atoms of Arg221A and Lys224 and four conserved water molecules. It is located near Asp189 of the S1 specificity site in an elongated solvent channel (8 x 18 A) formed by four antiparallel beta-strands between Cys182-Cys191 and Val213-Tyr228. This channel, extending from the active site to the opposite surface of the enzyme, was first noted in the hirudin-thrombin structure and contains about 20 conserved water molecules linked together by a hydrogen bonding network that connects to the main chain of thrombin. Although the antiparallel beta-strand interactions of the functional Na+ binding site are the same in prethrombin2, the loops between the strands are very different, so that Asp189 and Arg221A are not positioned properly for either substrate or Na+ binding in prethrombin2. A water molecule with octahedral coordination has also been identified in factor Xa at the topologically equivalent Na+ site position of thrombin. Since activated protein C shows enhanced activity with monovalant cation binding, the same position is probably utilized by Na+. Since thrombin crystals could not be grown in the absence of Na+, the cation was leached from Na(+)-bound thrombin crystals by diffusion/exchange. Although both Na+ and their coordinating water molecules were removed from the Na+ binding sites, the remainder of the thrombin structure was, unexpectedly, the same. The lack of an allosteric change is most likely attributable to crystal packing effects. Thus, the structure of the slow form remains to be established crystallographically.

Binding Sites↗
PubMed1997

[Surgical management for giant retinal tear].

OBJECTIVE: To study the effect of surgical management for giant retinal tear (GRT). METHODS: A standard three-point vitrectomy with silicone oil intraocular injection was performed on 41 cases. Of them, scleral buckling was also performed on 35 cases and lensectomy, on 17 cases. The basal vitreous gel and peri-retinal membranes were resected completely in all the cases. Air-fluid exchange, retinal tack or liquid perfluorocarbon were used to unroll and flatten the flap of the GRTs. Cryopexy or endophotocoagulation were applied to close the GRTs. RESULTS: In the follow-up for 3-39 months (mean 11.6 months), total retinal attachment was achieved in 29 cases, macular retinal attachment in 7 cases, and no retinal attachment in 5 cases. The final visual acuities were 0.01-0.05 in 6 cases, 0.06-0.1 in 17 cases, 0.2-0.5 in 11 cases and 0.6-1.0 in 2 cases. CONCLUSIONS: The key factor of successful operation is to unroll and flatten the flap of GRTs completely. Scleral buckling shows advantages and disadvantages, while appropriate scleral buckling is necessary in GRTs with proliferative vitreo-retinopathy. Postoperative further proliferation is the main factor affecting the long term effect of the treatment.

Adolescent↗
PubMed1997

[Primary study of bacterial adhesion of prosthetic valve materials].

The adhesion of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans to Dacron and pyrolite carbon was measured in vitro with plate counting. The experimental result showed: the bacterials used in the experiment have adhesion to prosthetic valve materials; the bacterials have stronger adhesion to Dacron than to Pyrolite carbon; the bacterial adhesive capacity is significantly different and is affected by mechanical and chemical nature of biomaterials; Staphylococcur aureus has the strongest adhesion to Dacron, and Pseudomonas aeruginosa has the strongest adhesion to pyrolite carbon in all bacterials.

Bacterial Adhesion↗
PubMed1996

Crystallization and initial spectroscopic characterization of the heme-containing dehaloperoxidase from the marine polychaete Amphitrite ornata.

The heme-containing dehaloperoxidase from Amphitrite ornata was crystallized from an unbuffered solution containing 30% PEG 8000 and 200 mM ammonium sulfate by the hanging-drop vapor-diffusion method. Dark-red bipyramidal crystals are orthorhombic in space group P2(1)2(1)2(1) with unit-cell dimensions a = 68.5, b = 68.4 and c = 61.1 A. The asymmetric unit contains two subunits related by a non-crystallographic twofold axis. The crystals scatter beyond 2 A resolution. The native data have been collected and one single-site mercury derivative has been found. SIRAS phasing was used to determine the positions of the heme Fe atoms and structure determination is in progress. A preliminary spectroscopic investigation indicates that the heme is protoporphyrin IX and its coordination sphere resembles that of a typical heme peroxidase, i.e. histidine ligated. Detailed spectroscopic and electrochemical studies are now under way.

Journal Article↗