Relationship of conserved residues in the IMP binding site to substrate recognition and catalysis in Escherichia coli adenylosuccinate synthetase

Gln34, Gln224, Leu228, and Ser240 are conserved residues in the vicinity of bound IMP in the crystal structure of Escherichia coli adenylosuccinate synthetase. Directed mutations were carried out, and wild-type and mutant enzymes were purified to homogeneity. Circular dichroism spectroscopy indicated no difference in secondary structure between the mutants and the wild-type enzyme in the absence of substrates. Mutants L228A and S240A exhibited modest changes in their initial rate kinetics relative to the wild-type enzyme, suggesting that neither Leu228 nor Ser240 play essential roles in substrate binding or catalysis. The mutants Q224M and Q224E exhibited no significant change in KmGTP and KmASP and modest changes in KmIMP relative to the wild-type enzyme. However, kcat decreased 13-fold for the Q224M mutant and 10(4)-fold for the Q224E mutant relative to the wild-type enzyme. Furthermore, the Q224E mutant showed an optimum pH at 6.2, which is 1.5 pH units lower than that of the wild-type enzyme. Tryptophan emission fluorescence spectra of Q224M, Q224E, and wild-type proteins under denaturing conditions indicate comparable stabilities. Mutant Q34E exhibits a 60-fold decrease in kcat compared with that of the wild-type enzyme, which is attributed to the disruption of the Gln34 to Gln224 hydrogen bond observed in crystal structures. Presented here is a mechanism for the synthetase, whereby Gln224 works in concert with Asp13 to stabilize the 6-oxyanion of IMP.

Common bile duct ligation in the rat: a model of intrapulmonary vasodilatation and hepatopulmonary syndrome

Hepatopulmonary syndrome (HPS) causes impaired oxygenation due to intrapulmonary vasodilatation in patients with cirrhosis. Chronic common bile duct ligation (CBDL) in the rat results in gas-exchange abnormalities similar to HPS, but intrapulmonary vasodilatation has not been evaluated. We assess intrapulmonary vasodilatation, measured in vivo, after CBDL. Sham, 2- and 5-wk CBDL, and 3-wk partial portal vein ligated (PVL) rats had hepatic and lung injury, portal pressure, and arterial blood gases assessed. The pulmonary microcirculation was evaluated by injecting microspheres (size range 5.5-10 microm) intravenously and measuring the size and number of microspheres bypassing the lungs in arterial blood. CBDL animals developed progressive hepatic injury and portal hypertension accompanied by gas-exchange abnormalities and intrapulmonary vasodilatation. PVL animals, with a similar degree of portal hypertension, did not develop intrapulmonary vasodilatation or abnormal gas exchange. No lung injury was observed. CBDL, but not PVL, causes progressive intrapulmonary vasodilatation, which accompanies worsening arterial gas exchange. These findings validate CBDL as a model to study HPS.

Lipids and membranes in the organic matrix of urinary calcific crystals and stones

The ultrastructure of the organic matrix of demineralized urinary stones was examined by standard transmission and scanning electron microscopy as well as after malachite green-glutaraldehyde fixation. Crystal ghosts of both calcium oxalate and calcium phosphate were made of amorphous material and were dispersed in a matrix containing amorphous, fibrillar, and membranous substances. Malachite green positive material was seen to be associated with the ghosts, as well as with the membranous and fibrillar components of the organic matrix. Calcium oxalate and calcium-phosphate crystals, induced in human urine in vitro were also found to be associated with an organic matrix containing lipids and proteins. It is suggested that the intimate association between crystals and lipids is a result of the involvement of cellular membranes in the nucleation of these crystals.

Cross-linking CD7 on myeloblasts results in granulocyte-macrophage colony-stimulating factor production

CD7+CD34+ lymphohematopoietic progenitor cells in bone marrow are capable of differentiating into either lymphocytes or myeloid cells. The mechanism whereby these bipotent progenitor cells are regulated is not yet clear. In this study, we investigated the role CD7 may play in the development of bipotent cells using two myeloid progenitor cell lines, KG-1 and KG-1a, as models for such cells. Our data showed that cross-linking CD7 on KG-1 and KG-1a cells induced transcription, translation, and secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF). Anti-CD7 antibody also augmented the colony formation by KG-1 cells. Protein synthesis in KG-1 cells also increased as a result of anti-CD7 stimulation. These phenomena could be blocked by anti-GM-CSF, and supported the notion that the secreted GM-CSF was the primary mediator of CD7 effects. Together, these findings suggest that the interaction between CD7 and its putative ligand may play an important role in hematopoietic development.

Refined crystal structures of guanine nucleotide complexes of adenylosuccinate synthetase from Escherichia coli

Structures of adenylosuccinate synthetase from Escherichia coli complexed with guanosine-5'-(beta,gamma-imido) triphosphate and guanosine-5'-(beta,gamma-methylene)triphosphate in the presence and the absence of Mg2+ have been refined to R-factors below 0.2 against data to a nominal resolution of 2.7 A. Asp333 of the synthetase hydrogen bonds to the exocyclic 2-amino and endocyclic N1 groups of the guanine nucleotide base, whereas the hydroxyl of Ser414 and the backbone amide of Lys331 hydrogen bond to the 6-oxo position. The side chains of Lys331 and Pro417 pack against opposite faces of the guanine nucleotide base. The synthetase recognizes neither the N7 position of guanine nucleotides nor the ribose group. Electron density for the guanine-5'-(beta,gamma-imido) triphosphate complex is consistent with a mixture of the triphosphate nucleoside and its hydrolyzed diphosphate nucleoside bound to the active site. The base, ribose, and alpha-phosphate positions overlap, but the beta-phosphates occupy different binding sites. The binding of guanosine-5'-(beta,gamma-methylene)triphosphate to the active site is comparable with that of guanosine-5'-(beta, gamma-imido)triphosphate. No electron density, however, for the corresponding diphosphate nucleoside is observed. In addition, electron density for bound Mg2+ is absent in these nucleotide complexes. The guanine nucleotide complexes of the synthetase are compared with complexes of other GTP-binding proteins and to a preliminary structure of the complex of GDP, IMP, Mg2+, and succinate with the synthetase. The enzyme, under conditions reported here, does not undergo a conformational change in response to the binding of guanine nucleotides, and minimally IMP and/or Mg2+ must be present in order to facilitate the complete recognition of the guanine nucleotide by the synthetase.

Production and characterization of the extracellular domain of human CD7 antigen: further evidence that CD7 has a role in T cell signaling

CD7 is a T cell-associated antigen which appears early in ontogeny and persists on circulating T cells. It appears to have a significant role in T cell development and function. The precise mechanism by which this molecule mediates its effect is not known. In this paper, we expressed the extracellular domain of CD7 in the baculovirus system and used this product to study the function CD7 might have in T cell activation. The recombinant protein was found to be structurally similar to the native CD7 and recognized by monoclonal and polyclonal antibodies to CD7. This protein inhibited T cell proliferation induced by anti-CD3/anti-CD7 costimulation. It also inhibited the augmentation effect of anti-CD7 on suboptimal PHA stimulation. However, it did not block T cell proliferation induced by optimal doses of PHA, staphylococcal entertoxin A or B. Interestingly, the recombinant protein inhibited antigenic- and alloantigenic-induced T cell proliferation. The latter finding strongly suggests that a ligand for CD7 exists and crosslinking CD7 by this ligand may be responsible for the costimulatory role it plays in T cell activation.

Detection of creatinine by a designed receptor

An artificial receptor has been designed to bind creatinine with a color change (chromogenic response) caused by proton transfer from one end of the receptor to the other. The receptor was synthesized and found to extract creatinine from water into chlorocarbon solvents. The color change in the organic layer is specific for creatinine relative to other organic solutes, and it is selective for creatinine relative to sodium, potassium, and ammonium ions. The chromogenic mechanism is revealed by x-ray crystal structures of creatinine, the free receptor, and the complex, showing "induced fit" binding resulting from electronic complementarity between host and guest.

Modular structural elements in the replication origin region of Tetrahymena rDNA

Computer analyses of the DNA replication origin region in the amplified rRNA genes of Tetrahymena thermophila identified a potential initiation zone in the 5'NTS [Dobbs, Shaiu and Benbow (1994), Nucleic Acids Res. 22, 2479-2489]. This region consists of a putative DNA unwinding element (DUE) aligned with predicted bent DNA segments, nuclear matrix or scaffold associated region (MAR/SAR) consensus sequences, and other common modular sequence elements previously shown to be clustered in eukaryotic chromosomal origin regions. In this study, two mung bean nuclease-hypersensitive sites in super-coiled plasmid DNA were localized within the major DUE-like element predicted by thermodynamic analyses. Three restriction fragments of the 5'NTS region predicted to contain bent DNA segments exhibited anomalous migration characteristic of bent DNA during electrophoresis on polyacrylamide gels. Restriction fragments containing the 5'NTS region bound Tetrahymena nuclear matrices in an in vitro binding assay, consistent with an association of the replication origin region with the nuclear matrix in vivo. The direct demonstration in a protozoan origin region of elements previously identified in Drosophila, chick and mammalian origin regions suggests that clusters of modular structural elements may be a conserved feature of eukaryotic chromosomal origins of replication.

A single-stranded DNA binding protein that specifically recognizes cis-acting sequences in the replication origin and transcriptional promoter region of Tetrahymena rDNA

Type I repeat sequences are evolutionarily conserved sequence elements found in the replication origin and transcriptional promoter region of the rRNA genes (rDNA) in Tetrahymena thermophila. An abundant single-stranded DNA binding protein, ssA-TIBF, specifically interacts with the A-rich strand of the Type I repeat sequence. Quantitative binding competition experiments performed with purified ssA-TIBF demonstrate that the binding site for ssA-TIBF includes sequences both within the conserved 33 nt element and in a 3' flanking region: addition of the 3' flanking sequence to the Type I repeat oligonucleotide increases the binding affinity of ssA-TIBF by nearly 100-fold (apparent Kd = 3.0 x 10(-10) M). A mutation in the ssA-TIBF binding site previously shown to be the determinant of an rDNA replication defect in vivo results in a 25-fold decrease in ssA-TIBF binding affinity in vitro. ssA-TIBF also binds with high affinity to a copy of the Type I repeat sequence within the essential promoter region defined by in vitro transcription assays. The affinity of ssA-TIBF for the promoter repeat, which differs from other copies of the repeat at 8 out of 33 positions, is at least equal to its affinity for the Type I repeat sequences in the origin region. The biochemical properties of ssA-TIBF in vitro suggest that it could play a role in both replication and transcription of Tetrahymena rDNA in vivo.

Identification and characterization of a putative telomere end-binding protein from Tetrahymena thermophila

Telomeric DNA of Tetrahymena thermophila consists of a long stretch of (TTGGGG)n double-stranded repeats with a single-stranded (TTGGGG)2 3' overhang at the end of the chromosome. We have identified and characterized a protein that specifically binds to a synthetic telomeric substrate consisting of duplex DNA and the 3' telomeric repeat overhang. This protein is called TEP (telomere end-binding protein). A change from G to A in the third position of the TTGGGG overhang repeat converts the substrate to a human telomere analog and reduces the binding affinity approximately threefold. Changing two G's to C's in the TTGGGG repeats totally abolishes binding. However, permutation of the Tetrahymena repeat sequence has only a minor effect on binding. A duplex structure adjacent to the 3' overhang is required for binding, although the duplex need not contain telomeric repeats. TEP does not bind to G-quartet DNA, which is formed by many G-rich sequences. TEP has a greatly reduced affinity for RNA substrates. The copy number of TEP is at least 2 x 10(4) per cell, and it is present under different conditions of cell growth and development, although its level varies. UV cross-linking experiments show that TEP has an apparent molecular mass of approximately 65 kDa. Unlike other telomere end-binding proteins, TEP is sensitive to high salt concentrations.

Tissue inhibitor of metalloproteinases-1 is decreased and activated gelatinases are increased in chronic wounds

The balance between matrix deposition and tissue turnover is fundamental in wound healing. It is likely that the balance between proteolytic enzymes and their inhibitors contributes to this balance. Matrix metalloproteinases are clearly important in tissue turnover, but their roles in wound healing are poorly understood. To investigate this, fluid from healing wounds resulting from mastectomies was collected from 1 h to 10 d post-surgery, and was analyzed for tissue inhibitor of metalloproteinases-1 concentrations. In all cases, tissue inhibitor of metalloproteinases-1 levels were initially comparable to those in serum, but increased rapidly to significantly higher levels within two days, with a tenfold average increase for five patients. On the other hand, zymography revealed that gelatinase A (72 kDa) levels increased moderately, whereas gelatinase B levels (92 kDa) decreased an average of twofold within 4 d. In contrast, fluid from chronic wounds had significantly more gelatinolytic activity, including lower-molecular-weight proteinase species that may represent activated or superactivated gelatinase fragments, as suggested by immunoprecipitation with specific antibodies. Tissue inhibitor of metalloproteinases-1 levels were lower in chronic than in healing wounds. These data may indicate that excess proteolysis in chronic wounds retards successful healing, and results from an imbalance of proteinase and inhibitors, as well as the presence of higher levels of activated metalloproteinases.

Identification of DNA-binding proteins that recognize a conserved type I repeat sequence in the replication origin region of Tetrahymena rDNA

An origin of DNA replication has been mapped within the 5' non-transcribed spacer region of the amplified macronuclear rRNA genes (rDNA) of Tetrahymena thermophila. Mutations in 33 nt conserved AT-rich Type I repeat sequences located in the origin region cause defects in the replication and/or maintenance of amplified rDNA in vivo. Fe(II)EDTA cleavage footprinting of restriction fragments containing the Type I repeat showed that most of the conserved nucleotides were protected by proteins in extracts of Tetrahymena cells. Two classes of proteins that bound the Type I repeat were identified and characterized using synthetic oligonucleotides in electrophoretic mobility shift assays. One of these, ds-TIBF, bound preferentially to duplex DNA and exhibited only moderate specificity for Type I repeat sequences. In contrast, a single-stranded DNA-binding protein, ssA-TIBF, specifically recognized the A-rich strand of the Type I repeat sequence. Deletion of the 5' or 3' borders of the conserved sequence significantly reduced binding of ssA-TIBF. The binding properties of ssA-TIBF, coupled with genetic evidence that Type I sequences function as cis-acting rDNA replication control elements in vivo, suggest a possible role for ssA-TIBF in rDNA replication in Tetrahymena.

Effects of temporal smearing on temporal resolution, frequency selectivity, and speech intelligibility

Envelopes of speech were smeared in 23 parallel frequency channels. The smeared speech was presented to normal-hearing listeners, and the effects of different smearing magnitudes on speech intelligibility were measured by obtaining speech recognition scores. It was demonstrated theoretically and experimentally that the system consisting of the computer smearing and the auditory system had reduced temporal resolution but nearly normal frequency resolution. Speech intelligibility of the processed vowel-consonant nonsense syllables was tested for low- and high-pass filter conditions. The overall speech recognition scores as well as the recognition scores of the consonants grouped according to articulatory features were analyzed. The results indicated that smearing with a narrow temporal window did not degrade speech. The larger equivalent rectangular durations (ERDs) of the resultant temporal window (RTW) of the combined system (temporal smearing plus auditory system) produced a small but significant reduction in speech intelligibility for the low-pass filter condition. Scores for the RTWs > 16 ms were significantly different from the score for the 7.7-ms RTW for the high-pass filter condition, but this effect was small and did not differ across articulatory features.

A model to evaluate and maximize hearing aid performance by integrating the articulation index across listening conditions

A method for integrating the articulation index (AI) across listening conditions was developed and applied to a preliminary model for evaluating and optimizing prescriptions of hearing aid characteristics. The model takes hearing threshold, masking of noise, self-masking of speech, high level cochlear distortion, and the peak-clipping effects of a hearing aid into account. The integrated AI (IAI) across a range of listening conditions is used as a criterion for evaluating a specific hearing aid response characteristic and calculating an optimal frequency-gain characteristic that maximizes the IAI. For a high-frequency hearing loss, the frequency-gain characteristics and IAI's derived from an optimal IAI (OIAI), POGO, and NAL prescriptions are compared for two of listening situations: a quiet setting and a setting with a signal-to-noise ratio of -3 dB. The results predict that, in quiet, the OIAI prescription is not significantly different from the well-established prescriptive procedures such as the POGO and the NAL. For the noise condition, however, the optimal IAI model is predicted to be better in terms of speech intelligibility.

Experimental research on treatment of hypertension with acupuncture

The effects of acupuncture on blood pressure, microcirculation of bulbar conjunctiva and hemorheology in spontaneous hypertensive rats (SHRs) were observed. The mechanism of acupuncture to lower blood pressure is discussed from the viewpoint of microcirculation and hemorheology. SHRs and Wistar rats of both sexes weighing about 250g were divided into three groups: 1. Acupuncture group of 15 SHRs, in which Quchi (LI 11) and Taichong (Liv 3), Hegu (LI 4) and Zusanli (St 36) were selected and punctured twice a day with the needle retained for 15 minutes and the reducing method by twisting and twirling the needle used, 15 days constituting a course; 2. Control group of 10 SHRs; 3. Control group of 10 normal Wistar rats. All rats in groups 2 and 3 were treated in the same way as in Group 1 except for the acupuncture. It was found that the morphology and blood flow of bulbar conjunctiva microcirculation in SHRs were obviously abnormal: the capillaries with blood flow were reduced in number, the arterioles were spasmodic and of smaller diameter, the venules were dilated due to blood stasis which showed a slow granular flow of blood, the blood viscosity was increased, hematocrit increased, and the time for RBC electrophoresis prolonged. The blood was in a state of high viscosity, high concentration and high aggregation. After acupuncture treatment the blood pressure not only fell, but the morphology and blood flow of bulbar conjunctiva microcirculation and the hemorheology of SHRs all improved remarkably.(ABSTRACT TRUNCATED AT 250 WORDS)

An experimental study on acupuncture anti-hemorrhagic shock

The effect of acupuncture at Neiguan (P 6) on regulating hemorrhagic shock in 90 rabbits was observed. All the results suggested that acupuncture at Neiguan could raise blood pressure, protect cardiac pump function, correct the disturbance of secretion and metabolism of humoral factors, reduce blood adhesion to normal level and thus achieve anti-hemorrhagic shock. This study has provided scientific basis for expounding the mechanism of acupuncture in anti-shock.

Synergistic effects of cytokine and hyperthermia on cytotoxicity in HT-29 cells are not mediated by alteration of induced protein levels

In this study, we investigated the mechanism of synergistic effects of cytokine and hyperthermia on cytotoxicity in HT-29. When cells were heated at 42 degrees C in the presence of recombinant human tumor necrosis factor (rhTNF-alpha), recombinant interferon-gamma (rhIFN-gamma), or in a combination of both, a synergistic increase in the cytotoxic effects of the respective drugs was observed. We hypothesized that alteration of cytokine or heat-induced polypeptides synthesis was responsible for a synergistic interaction between heat and cytokine. Five heat shock proteins (HSPs, M(r) 110,000, 100,000, 90,000, 70,000, and 28,000) were preferentially synthesized during chronic heating at 42 degrees C. In contrast, the synthesis of two proteins (M(r) 60,000 and 29,000) was induced by treatment with rhIFN-gamma (1,000 U/ml). Although the combination of chronic hyperthermia (42 degrees C) with TNF-alpha, IFN-gamma, or TNF-alpha + IFN-gamma increased cytotoxicity, alteration/induction of polypeptides was not correlated with the synergistical cytotoxic effects of cytokine and heat. Thus, the synergistic effects of cytokine and hyperthermia are not mediated through an induction of polypeptides.

Current management of hepatocellular carcinoma

After a long, hopeless period in the management of hepatocellular carcinoma (HCC), the diagnosis and treatment of HCC have progressed remarkably in the past decade. In particular the discovery of asymptomatic HCC in the early 1970s opened up a new era in clinical research of HCC. With the progress in the diagnostic imaging of liver tumors, a 1 cm hepatic mass can now be detected. It is especially worth noting that a 5-year survival rate of 72.9% has been achieved after the resection of the tumor in asymptomatic HCC patients. The role of surgery in the treatment of HCC has become more important. Various modalities of medical treatment and combination therapy have been recommended and used. Despite the progress in the early diagnosis and treatment of HCC, a complete cure is very rare. Problems to be studied include new tumor markers for the early detection of alpha-fetoprotein (AFP)-negative HCC, the development of more specific treatments for unresectable HCC with uncompensated cirrhosis, and an effective approach to preventing recurrence and metastasis after radical resection.

Cytoreduction and sequential resection: a hope for unresectable primary liver cancer

For decades, unresectable primary liver cancer (PLC) determined by operation was incurable. However, a retrospective study of 24 years' materials with unresectable PLC indicated that 5-year survival of unresectable PLC has increased from 0% in 1966-1977 (n = 137) to 16.9% in 1978-1989 (n = 345). This encouraging improvement was mainly a result of cytoreduction therapy followed by sequential resection. Multimodality combination treatment with hepatic artery ligation, plus hepatic artery infusion with chemotherapy, plus radioimmunotherapy (or radiotherapy) yielded the highest sequential resection rate (30.6%) and 5-year survival (28.0%) as compared with double combination and single modality treatment. The 5-year survival of 33 patients receiving sequential resection after cytoreduction therapy was 63.2%. It is suggested that cytoreduction and sequential resection might offer a hope for surgically verified unresectable PLC.