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T Ziv

Publications and source records attributed to T Ziv.

13 recordsLinked to original sources
PubMed2001

Is the unique negatively charged polypeptide of crayfish yolk HDL a component of crustacean vitellin?

The yolk protein of Cherax quadricarinatus contains six major high-density lipoprotein (HDL) subunits with the approximate molecular masses of 177, 155, 106, 95, 86, and 75 kDa, of which only the 106-kDa polypeptide is negatively charged. On the basis of their molecular weights, time of appearance and disappearance, their floating density and susceptibility to enzyme degradation (by a serine proteinase), these six HDL polypeptides were classified into two subgroups. One group comprises the higher-molecular-weight compounds above 106 kDa, and the other includes the lower-molecular-weight compounds up to 95 kDa. Other than being different from the lower-molecular-weight polypeptides, the negatively charged 106-kDa polypeptide was significantly different from members of its higher-molecular-weight group belonging to a different, less abundant, yolk protein as shown by HPLC separation. Immunological studies and peptide mapping in which the 106-kDa polypeptide did not show similarity to any of the other HDL components confirmed these differences. Moreover, the amino acid composition of the 106-kDa polypeptide was different from that of known vitellin from other crustacean species. This unique negatively charged polypeptide presents an enigma as it is known to be a secondary vitellogenic-related HDL polypeptide, immunolocalized in yolk globules; however, it is different to all the other HDL polypeptides, thus presenting the question whether it is indeed a component of "classical" crustacean vitellin.

Animals↗
PubMed2001

Autophosphorylation restrains the apoptotic activity of DRP-1 kinase by controlling dimerization and calmodulin binding.

DRP-1 is a pro-apoptotic Ca2+/calmodulin (CaM)-regulated serine/threonine kinase, recently isolated as a novel member of the DAP-kinase family of proteins. It contains a short extra-catalytic tail required for homodimerization. Here we identify a novel regulatory mechanism that controls its pro-apoptotic functions. It comprises a single autophosphorylation event mapped to Ser308 within the CaM regulatory domain. A negative charge at this site reduces both the binding to CaM and the formation of DRP-1 homodimers. Conversely, the dephosphorylation of Ser308, which takes place in response to activated Fas or tumour necrosis factor-alpha death receptors, increases the formation of DRP-1 dimers, facilitates the binding to CaM and activates the pro-apoptotic effects of the protein. Thus, the process of enzyme activation is controlled by two unlocking steps that must work in concert, i.e. dephosphorylation, which probably weakens the electrostatic interactions between the CaM regulatory domain and the catalytic cleft, and homodimerization. This mechanism of negative autophosphorylation provides a safety barrier that restrains the killing effects of DRP-1, and a target for efficient activation of the kinase by various apoptotic stimuli.

Amino Acid Sequence↗
PubMed2000

Proteolysis of bacteriophage lambda CII by Escherichia coli FtsH (HflB).

FtsH (HflB) is a conserved, highly specific, ATP-dependent protease for which a number of substrates are known. The enzyme participates in the phage lambda lysis-lysogeny decision by degrading the lambda CII transcriptional activator and by its response to inhibition by the lambda CIII gene product. In order to gain further insight into the mechanism of the enzymatic activity of FtsH (HflB), we identified the peptides generated following proteolysis of the phage lambda CII protein. It was found that FtsH (HflB) acts as an endopeptidase degrading CII into small peptides with limited amino acid specificity at the cleavage site. beta-Casein, an unstructured substrate, is also degraded by FtsH (HflB), suggesting that protein structure may play a minor role in determining the products of proteolysis. The majority of the peptides produced were 13 to 20 residues long.

ATP-Dependent Proteases↗
PubMed1999

26 S proteasome-mediated production of an authentic major histocompatibility class I-restricted epitope from an intact protein substrate.

Peptides displayed on the cell surface by major histocompatibility class I molecules (MHC class I) are generated by proteolytic processing of protein-antigens in the cytoplasm. Initially, antigens are degraded by the 26 S proteasome, most probably following ubiquitination. However, it is unclear whether this proteolysis results in the generation of MHC class I ligands or if further processing is required. To investigate the role of the 26 S proteasome in antigen presentation, we analyzed the processing of an intact antigen by purified 26 S proteasome. A recombinant ornithine decarboxylase was produced harboring the H-2K(b)-restricted peptide epitope, derived from ovalbumin SIINFEKL (termed ODC-ova). Utilizing recombinant antizyme to target the antigen to the 26 S proteasome, we found that proteolysis of ODC-ova by the 26 S proteasome resulted in the generation of the K(b)-ligand. Mass spectrometry analysis indicated that in addition to SIINFEKL, the N-terminally extended ligand, HSIINFEKL, was also generated. Production of SIINFEKL was linear with time and directly proportional to the rate of ODC-ova degradation. The overall yield of SIINFEKL was approximately 5% of the amount of ODC-ova degraded. The addition of PA28, the 20 S, or the 20 S-PA28 complex to the 26 S proteasome did not significantly affect the yield of the antigenic peptide. These findings demonstrate that the 26 S proteasome can efficiently digest an intact physiological substrate and generate an authentic MHC class I-restricted epitope.

Amino Acid Sequence↗
PubMed1999

Developmental regulation of cmp1, a gene encoding a multidomain conidiospore surface protein of Trichoderma.

A gene encoding a developmentally regulated polypeptide of Trichoderma (strain ATCC 32173) was isolated, with the help of an antibody against a 62-kDa protein whose abundance strongly increases during photoinduced sporulation. The amino acid sequence deduced from this gene, cmp1 (conidial multidomain protein), is a 135-kDa polypeptide consisting of several domains. Although reminiscent of known structural modules, two of the domains may define novel families. The protein is apparently processed to give the 62-kDa species. Immunogold labeling electron microscopy localized the antigen to the membrane or inner wall layers. The mRNA is strongly up-regulated during sporulation. At least part of this regulation is likely to be conferred by several elements identified in the upstream region, with homology to elements recognized by fungal transcription factors for regulation by conidiation, light, and nitrogen stress. The developmental regulation, cell surface location, and modular structure suggest a function in cell-cell interactions, detection of the wall by the cell, or anchoring of the plasma membrane to the wall.

Amino Acid Sequence↗
PubMed1999

Cauda equina syndrome due to lumbosacral arachnoid cysts in children.

We describe the clinical, neuroradiological and surgical aspects of two children in whom symptoms attributable to cauda equina compression were caused by spinal arachnoid cysts. The first patient presented with recurrent urinary tract infections due to neurogenic bladder dysfunction, absent deep tendon reflexes and sensory deficit in the lower limbs. The second child presented with unstable gait as a result of weakness and diminished sensation in the lower extremities. Spinal magnetic resonance imaging revealed a lumbosacral arachnoid cyst in both patients. During surgery the cysts were identified and excised. Two years after surgery, the sensory deficits of the first patient have disappeared and patellar and ankle reflexes can be elicited, but there is no improvement in bladder function. Neurological examination of the second patient was normal. We conclude that the diagnosis of cauda equina syndrome should prompt a vigorous search for its aetiology. Lumbosacral arachnoid cysts are a rare cause of cauda equina syndrome in children.

Arachnoid Cysts↗
PubMed1999

Acute respiratory distress syndrome in children: a 10 year experience.

BACKGROUND: Acute respiratory distress syndrome is a well-recognized condition resulting in high permeability pulmonary edema associated with a high morbidity. OBJECTIVES: To examine a 10 year experience of predisposing factors, describe the clinical course, and assess predictors of mortality in children with this syndrome. METHODS: The medical records of all admissions to the pediatric intensive care unit over a 10 year period were evaluated to identify children with ARDS. Patients were considered to have ARDS if they met all of the following criteria: acute onset of diffuse bilateral pulmonary infiltrates of non-cardiac origin and severe hypoxemia defined by < 200 partial pressure of oxygen during > or = 6 cm H2O positive end-expiratory pressure for a minimum of 24 hours. The medical records were reviewed for demographic, clinical, and physiologic information including PaO2/forced expiratory O2, alveolar-arterial O2 difference, and ventilation index. RESULTS: We identified 39 children with the adult respiratory distress syndrome. Mean age was 7.4 years (range 50 days to 16 years) and the male:female ratio was 24:15. Predisposing insults included sepsis, pneumonias, malignancy, major trauma, shock, aspiration, near drowning, burns, and envenomation. The mortality rate was 61.5%. Predictors of death included the PaO2/FIO2, ventilation index and A-aDO2 on the second day after diagnosis. Nonsurvivors had significantly lower PaO2/FIO2 (116 +/- 12 vs. 175 +/- 8.3, P < 0.001), and higher A-aDO2 (368 +/- 28.9 vs. 228.0 +/- 15.5, P < 0.001) and ventilation index (43.3 +/- 2.9 vs. 53.1 +/- 18.0, P < 0.001) than survivors. CONCLUSIONS: Local mortality outcome for ARDS is comparable to those in tertiary referral institutions in the United States and Western Europe. The PaO2/FIO2, A-aDO2 and ventilation index are valuable for predicting outcome in ARDS by the second day of conventional therapy. The development of a local risk profile may allow early application of innovative therapies in this population.

Acute Disease↗
PubMed1998

A novel site for ubiquitination: the N-terminal residue, and not internal lysines of MyoD, is essential for conjugation and degradation of the protein.

The ubiquitin proteolytic pathway is a major system for selective protein degradation in eukaryotic cells. One of the first steps in the degradation of a protein via this pathway involves selective modification of epsilon-NH2 groups of internal lysine residues by ubiquitination. To date, this amino group has been the only known target for ubiquitination. Here we report that the N-terminal residue of MyoD is sufficient and necessary for promotion of conjugation and subsequent degradation of the protein. Substitution of all lysine residues in the protein did not affect significantly its conjugation and degradation either in vivo or in vitro. In cells, degradation of the lysine-less protein is inhibited by the proteasome inhibitors MG132 and lactacystin. Inhibition is accompanied by accumulation of high molecular mass ubiquitinated forms of the modified MyoD. In striking contrast, wild-type MyoD, in which all the internal Lys residues have been retained but the N-terminus has been extended by fusion of a short peptide, is stable both in vivo and in vitro. In a cell-free system, ATP and multiple ubiquitination are essential for degradation of the lysine-less protein. Specific chemical modifications have yielded similar results. Selective blocking of the alpha-NH2 group of wild-type protein renders it stable, while modification of the internal Lys residues with preservation of the free N-terminal group left the protein susceptible to degradation. Our data suggest that conjugation of MyoD occurs via a novel modification involving attachment of ubiquitin to the N-terminal residue. The polyubiquitin chain is then synthesized on an internal Lys residue of the linearly attached first ubiquitin moiety.

Adenosine Triphosphate↗
PubMed1998

Ventilation index and outcome in children with acute respiratory distress syndrome.

The purpose of this investigation was to determine the predictive value of the ventilation index (VI) in children with acute respiratory distress syndrome (ARDS). We performed a 10-year retrospective chart review of children who were admitted to the Pediatric Intensive Care Unit with a diagnosis of ARDS. Acute respiratory distress syndrome was defined as acute onset of diffuse, bilateral pulmonary infiltrates of noncardiac origin, and severe hypoxemia, defined as the ratio of the arterial partial pressure of oxygen to the fraction of inspired oxygen of <200 and a positive end expiratory pressure of 6 cmH2O or greater. Records of daily arterial blood gas results and ventilator settings were reviewed, and the ventilation index (VI=partial pressure of arterial CO2 x peak airway pressure x respiratory rate/1,000) was calculated each time the measurements were made. These values were correlated with outcome (survival or nonsurvival). The VI was not different at the time of diagnosis of ARDS in the patients who lived, compared with those who subsequently died. However, by 3 to 5 days after study entry, the VI of nonsurvivors was significantly higher than for survivors (P < 0.05). The VI for survivors remained between 30 and 35 throughout the study period, whereas the VI of nonsurvivors continued to increase with time. A VI of >65 predicted death with a specificity and positive predictive value of >90% on days 3 through 9. We conclude that the VI provides a reliable prognostic marker in children with ARDS, and its increase above 65 indicates a need for orderly intervention with alternative modalities of care.

Adolescent↗
PubMed1992

Activin can generate ectopic axial structures in chick blastoderm explants.

We have recently shown that activin can induce the formation of axial structures from chick blastulae and that activin beta-B is transcribed, in the hypoblast of the chick, at the same stage that axial mesoderm is being induced. It was not clear, however, whether activin was merely allowing the central epiblastic cells to express a differentiated phenotype for which they were already prepared. This report shows that activin-containing medium (ACM) can act as an instructive inductor, which can change the fate of competent cells and bring about the formation of an ectopic embryonic axis. Furthermore, we show data that suggest that during normal development only one axis is obtained as a result of a carefully controlled inhibitory process.

Activins↗
PubMed1990

Activin can induce the formation of axial structures and is expressed in the hypoblast of the chick.

We show that PIF/activin can induce the formation of axial structures including a full-length notochord, segmented somites, and a neural tube in isolated epiblasts from chick blastulae. Using degenerate PCR primers, we have cloned a fragment of the activin beta B chain from chick hypoblast cDNA, and a fragment of the activin beta A chain from chick genomic DNA. Furthermore, we show that in the chick, activin is transcribed precisely when axial mesoderm is being induced. Since exogenous PIF/activin can induce the formation of axial structures and since activin beta B is transcribed at the time and place where the mesodermal axial structures are being induced, we propose that in the chick, activin B is the endogenous inducer of the body axis.

Activins↗
PubMed1990

Fibroblast growth factor during mesoderm induction in the early chick embryo.

A chick genomic clone that reveals a high degree of homology to the mammalian and Xenopus bFGF gene has been isolated. The pattern of expression of bFGF has been examined during early chick embryogenesis. RNA blot analysis revealed that chick bFGF is already transcribed at pregastrula stages. Immunolabeling analysis indicated that bFGF protein is present at these early developmental stages and is distributed evenly in the epiblast, hypoblast and marginal zone of the chick blastula. Substances that can inhibit FGF action were applied to early chick blastoderms grown in vitro under defined culture conditions (DCM). Both heparin and suramin were capable of blocking the formation of mesodermal structures in a dose-dependent manner. Our results indicate that FGF-like substances may need to be present for axial structures to develop although they may be acting earlier during the induction of non-axial mesoderm.

Amino Acid Sequence↗