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PubMed1992

Inferior vena cava filters. Indications, safety, effectiveness.

BACKGROUND: Preventing pulmonary embolization by interrupting vena caval flow has been attempted since 1893. Inferior vena cava (IVC) filters have been available for 20 years, and currently there are five filters commercially available in the United States (Greenfield filter, Titanium Greenfield filter, Simon-Nitinol filter, Bird's Nest filter, and LGM or Vena Tech filter) and two other filters under development (Amplatz filter and Günther filter). Although these devices are widely used, their clinical utility and safety have not been completely evaluated. Controlled clinical trials to determine the clinical role for IVC filters have not been attempted, but numerous case series describing the outcomes of the seven current filters have been published. We have systematically reviewed these studies to clarify what is known about the indications, safety, and effectiveness of IVC filters. METHODS: Using the MEDLINE database, all English-language publications since 1970 that included follow-up clinical information after filter insertion were reviewed and eight methodologic guidelines were employed to assess the scientific quality of the clinical information. RESULTS: Twenty-four case series were reviewed: 16 concerned the Greenfield filter (1632 patients), and eight dealt with newer designs (925 patients). Commonly noted methodologic problems included failure to report the initial extent of thromboembolic disease, incomplete description of the patient assembly process, and incomplete and potentially biased outcome assessment. Recurrent clinical pulmonary embolism was rare after filter placement, and only eight deaths from pulmonary embolism were reported. Filter complications were common but rarely life threatening; four (0.16%) deaths from filter complications were noted among the reviewed studies. Thrombotic complications following filter placement included insertion-site deep vein thrombosis and IVC obstruction. These events were rare, but they occurred with all filter types. CONCLUSIONS: Inferior vena cava filters appear to be effective in preventing recurrent pulmonary embolism. Despite the large published experience with IVC filters, many questions remain about their indications, safety, and effectiveness. Anticoagulant therapy, if not contraindicated, should be used in conjunction with filters. While there is no ideal filter, some situations call for specific filters. Filter selection and insertion require experience, modern angiographic technique, and collaboration between clinicians caring for patients and the interventional radiologists or surgeons inserting the device.

Anticoagulants↗
PubMed1992

Subunit folding and alpha delta heterodimer formation in the assembly of the nicotinic acetylcholine receptor. Comparison of the mouse and human alpha subunits.

We have used the mouse alpha (alpha M) and human alpha (alpha H) subunits to investigate the molecular mechanisms of assembly of the mammalian acetylcholine receptor (AChR) transiently expressed in COS cells. COS cells expressing hybrid receptors incorporating alpha H along with other mouse subunits exhibited a 2-fold higher level of surface alpha-bungarotoxin (BuTx) binding than cells expressing the wild-type mouse AChR. When expressed either alone or with the delta subunit in COS cells, alpha H acquired the BuTx binding conformation (alpha Tx) more efficiently than did alpha M. By oligonucleotide-directed mutagenesis we showed that 2 residues in the amino-terminal domain were responsible for the differences between alpha M and alpha H. Alpha MST, the modified mouse alpha subunit, both folded more efficiently to form alpha Tx and was more effective in forming a stable alpha delta heterodimer than was alpha M. The kinetics of alpha Tx and alpha delta heterodimer formation revealed that the delta subunit increased the conversion of immature forms of the alpha subunit into the BuTx binding form and therefore provides evidence for interaction between the delta subunit and the immature form of the alpha subunit. These results provide evidence of the importance of the amino-terminal domains of the AChR subunits in the assembly process.

Animals↗
PubMed2004

Human monoclonal antibodies that neutralize anthrax toxin by inhibiting heptamer assembly.

A panel of human anti-anthrax protective antigen IgG1 monoclonal antibodies were evaluated to determine the mechanism of toxin neutralization. AVP-22G12, AVP-1C6 and AVP-21D9 bound to the protective antigen with picomolar affinities to distinct non-overlapping linear epitopes. Two of the antibodies neutralized the anthrax toxin by completely inhibiting the protective antigen oligomer assembly process in vitro.

Antibodies, Monoclonal↗
PubMed2005

[Synthesis and SERS characterization of silver nanocubes].

Silver nanocubes were synthesized by reducing silver nitrate with ethylene glycol in the presence of poly(vinyl pyrrolidone) based on the report by Xia's group. Silver nanocubes were immobilized on silicon wafers by self-assembly processes. SERS activity of silver nanocubes was detected by using pyridine and SCN- respectively as probe molecules. The preliminary results show that the Raman intensities of pyridine and SCN- adsorbed at silver nanocubes were enhanced considerably, indicating that silver nanocubes can be used as a good SERS substrate. On the other hand, SERS combined with the probe molecule method can be used to characterize the optical property of silver nanocubes.

Ethylene Glycol↗
PubMed1975

Studies of the nature of herpesvirus-induced tumour-associated antigens induced by herpes simplex virus type 1 and further analysis of their relationship with squamous-cell carcinomas of the head and neck region.

The differences seen in levels of antibody response to HSV-TAA between non-laryngeal and laryngeal cancers in cured and untreated patient populations were due to the use of filtered sera. In previous and present studies using unfiltered sera, these differences were not noted. Of unfiltered sera from patients with squamous-cell carcinomas of the head and neck, 89% (49 out of 55) were positive for CF reactivity to HSV-TAA, and 44% of these unfiltered sera had titres of 1:4 or greater to 44 microng of antigen. The upper band of the antigen appears to be present in early provirus formation and is highly unstable whereas the lower band does not seem to be part of the assembly process.

Antibodies, Neoplasm↗
PubMed1990

Structure of the gene for rat nucleolar protein B23.

Protein B23 is an abundant RNA-associated nucleolar phosphoprotein involved in the ribosome assembly process. Previous studies showed that two forms of the protein (B23.1 and B23.2) are generated from a single gene via alternative splicing of 3' exons at the mRNA level (Chang, J. H., and Olson, M. O. J. (1989) J. Biol. Chem. 264, 11732-11737). We now report the structure of the complete B23 gene which spans 11-kilobases of DNA and contains 12 exons coding for the 294 amino acid residues. B23.1 mRNA is encoded by exons 1-9, 11, and 12, whereas exons 1-10 code for the B23.2 mRNA. Each exon codes for a relatively short segment of the protein (2-40 amino acid residues). The exons, which are distributed unevenly over the length of the gene, are separated by introns varying in size between 122 base pairs and 2.2 kilobases. Southern blot analyses using a probe derived from the untranslated segment of exon 10 suggests that a single expressed gene is present in the rat genome. Additional genomic clones contained apparent processed pseudogenes for protein B23. Primer extension studies and comparison with a processed pseudogene reveal a probable transcription initiation site at position -96 from the first ATG. The 5' region of the gene contains several possible regulatory elements. Three GC boxes which are potential binding sites for transcription factor Sp1 were found, including one within the first intron. A segment of about 1500 base pairs in the 5' region is unusually rich in the dinucleotide CpG. Although no CCAAT box was found a well-defined TATA box is present at position -126. The latter feature suggests that the B23 gene has some properties of tissue-specific genes in addition to the predominant characteristics of housekeeping genes.

Amino Acid Sequence↗
PubMed1985

Transmembrane channel-formation by five complement proteins.

Five serum proteins act in concert to form the membrane attack complex (MAC) of complement. The precursor proteins, C5, C6, C7, C8 and C9, are hydrophilic glycoproteins with molecular weights ranging from 70,000 to 180,000. When C5 is cleaved by the serine protease C5 convertase, nascent C5b is produced which forms together with C6 a soluble and stable bimolecular complex (C5b,6). Upon binding of C5b,6 to C7 a trimolecular complex (C5b-7) is formed, which expresses a metastable membrane binding site. Membrane-bound C5b-7 constitutes the receptor for C8 and the tetramolecular C5b-8 complex binds and polymerizes C9. During the assembly process the proteins undergo hydrophilic-amphiphilic transition and the end product consists of C5b-8 (Mr approx. 550,000) and of tubular poly C9 (Mr approx. 1,100,000). The functional channel size varies but its maximal diameter is approximately 10 nm. C9 polymerization appears to involve initial reversible associations of several C9 molecules, which leads to temperature dependent, constrained unfolding. Unfolded C9 monomers then associate laterally with each other and polymerization terminates with closure of the circular structure, which consists of 12-18 C9 monomers. Amino acid composition and sequence indicate that the N-terminal half of the single chain C9 molecule is hydrophilic and the C-terminal half rather hydrophobic. Phospholipid binding and insertion into membranes are functions of the C-terminal portion of the molecule.

Amino Acid Sequence↗
PubMed1989

Phospholipid storage in the secretory granule of the mast cell.

A spontaneous membrane assembly process has been postulated to account for the rapid perigranular membrane enlargement which occurs during mast cell secretory granule activation. This process requires the presence of a phospholipid store in the quiescent granule. By using purified granules with intact membranes we have determined the total phospholipid content of the average quiescent granule. The results suggest that the average quiescent granule contains sufficient phospholipid to sustain at least a trebling of its perigranular membrane surface area during activation. As much as two-thirds of the total cellular phospholipid is found in the granules, and since a large portion of this phospholipid is extruded into the extracellular space along with the granule matrix during exocytosis, it is implied that this phospholipid can serve as the substrate for the formation of the lipid-derived mediators of inflammation.

Animals↗
PubMedDate not supplied

Perspectives for the chemotherapy of AIDS.

In the design of selective inhibitors of the human immunodeficiency virus (HIV), the etiologic agent of AIDS, various steps of the virus replicative cycle could be envisaged as targets, i.e. virus adsorption to its cellular receptor (or another early event in virus replication such as penetration or uncoating), transcription of the viral RNA genome to proviral DNA (reverse transcription), trans-activation of viral mRNA transcription and translation, and, finally, virus release ("budding", or another late event in virus replication such as the assembly process). Although some potent HIV inhibitors such as heparin and dextran sulfate may interfere with an early step of the virus replicative cycle (adsorption) and others (interferon and interferon inducers) are assumed to act at a late step (budding), the majority of the anti-HIV agents appear to act at the reverse transcriptase level. Most of these reverse transcriptase inhibitors belong to the class of the 2',3'-dideoxynucleosides (ddN), and within this class of compounds a variety of 2',3'-dideoxy-, 2',3'-didehydro-2',3'-dideoxy-, 3'-azido-2',3'-dideoxy- and 3'-fluoro-2',3'-dideoxyribosides of both purines and pyrimidines have been described as potent and selective anti-HIV agents. Akin to 3'-azido-2',3'-dideoxythymidine (AZT), the sole anti-HIV compound that has so far been licensed for clinical use in the treatment of AIDS, all other ddN analogues are postulated to interact as competitive inhibitors (with respect to the natural substrates) and/or chain terminators of the HIV reverse transcriptase. To do so, the ddN analogues need first to be phosphorylated by cellular kinases to the corresponding 5'-triphosphates (ddNTPs), and together with the affinity of the ddNTPs for the HIV reverse transcriptase (relative to their affinity for the cellular DNA polymerases), the extent by which the ddNs are phosphorylated to the ddNTPs are critical determinants of their potency and selectivity as anti-HIV agents. Much more remains to be learned about the in vivo efficacy of the 2',3'-dideoxynucleoside analogues, and their pharmacokinetic and toxicological properties, before their true potential in the treatment of AIDS can be fully assessed.

Acquired Immunodeficiency Syndrome↗
PubMed1985

M13 procoat inserts into liposomes in the absence of other membrane proteins.

Procoat, the precursor form of the major coat protein of coliphage M13, assembles into the Escherichia coli inner membrane and is cleaved to mature coat protein by leader peptidase. This assembly process has previously been reconstituted using lipids and purified leader peptidase in a cell-free protein synthesis reaction (Watts, C., Silver, P., and Wickner, W. (1981) Cell 25, 347-353; Ohno-Iwashita, Y., and Wickner, W. (1983) J. Biol. Chem. 258, 1895-1900). We now report that procoat can also cross a liposomal membrane composed of only purified phospholipids; leader peptidase is not needed to catalyze insertion. When procoat is synthesized in vitro in the presence of liposomes with encapsulated chymotrypsin, the procoat inserts spontaneously through the membrane and is degraded. The protease was shown by several criteria to be in the lumen of the liposomes. These results demonstrate that the precursor form of an E. coli integral membrane protein can cross a membrane without the aid of leader peptidase or any other membrane proteins.

Capsid↗
PubMed1972

Intracellular sites of lipid synthesis and the biogenesis of mitochondria.

Experimental data are presented on the intracellular localization in rat liver of three enzymes which are involved in the biosynthesis of phosphatidylethanolamine and diphosphatidylglycerol. These enzymes are phosphatidylserine decarboxylase, CDP-diglyceride-l-alpha-glycerophosphate phosphatidyl transferase, and phosphatidylethanolamine-l-serine phosphatidyl transferase. It was found that the first two enzymes are primarily mitochondrial while the latter enzyme is primarily microsomal. The intracellular sites for the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and diphosphatidylglycerol are discussed, and the implications of their sites of biosynthesis on the assembly processes involved in the biogenesis of mitochondria are considered.

Amino Alcohols↗
PubMed1981

Physical characteristics of 16 S rRNA under reconstitution conditions.

The hydrodynamic shape and conformation of the 16 S ribosomal RNA in reconstitution buffer at both 4 degrees C and 37 degrees C were determined and compared with the corresponding properties of the 30 S ribosomal subunit at 4 degrees C in order to understand the role of the RNA molecule in the assembly of the 30 S subunit. At 4 degrees C, the 16 S rRNA has a sedimentation coefficient s020,w of 21.0 S, a diffusion coefficient D020,w of 1.72 X 10(-7) cm2/s, a frictional coefficient f/fmin of 2.37, and a hydrodynamic radius of 125 A. At 37 degrees C, the 16 S rRNA has a sedimentation coefficient s020,w of 18.4 S, a diffusion coefficient D020,w of 1.39 X 10(-7) cm2/s, a frictional coefficient f/fmin of 2.91, and a hydrodynamic radius of 153 A. At 4 degrees C, the 30 S subunit has a sedimentation coefficient s020,w of 31.8 S, a diffusion coefficient D020,w of 1.97 X 10(-7) cm2/s, a frictional coefficient f/fmin of 1.77, and a hydrodynamic radius of 109 A. These results suggested that the free RNA in solution at 4 degrees C is less folded than the RNA in the ribosomal subunit. At 37 degrees C, the free 16 S rRNA is unfolded when compared to the structure of the same RNA at 4 degrees C. This implies that the folding step accompanying the RI to RI transformation in the assembly process needs the presence of both the RNA and core proteins.

Centrifugation, Density Gradient↗
PubMed1983

Subunit dimers in sheep spleen apoferritin. The effect on iron storage.

Ferritin with high and low iron content, 2000 and 790 iron atoms/molecule, was isolated from the spleens of copper-poisoned and control lambs, respectively. Differences in the iron content in vivo were reflected in the properties of the apoferritin protein shells, since the apoprotein from the low iron ferritin took up iron relatively more slowly (0.52 +/- 0.09) and released it more rapidly (1.68 +/- 0.06) in vitro. Although the two types of apoferritin were indistinguishable in terms of surface charge (pI range 4.98-5.43) and in consisting of both heavy and light subunits, the subunit interactions differed markedly; 40-50% of the subunits of low iron ferritin were in dimers stable to reduction and carboxylmethylation, 4% mercaptoethanol, 8% sodium dodecyl sulfate, and 100 degrees C for 30 min, 70% formic acid, and 30% methanol. Subunit dimers were also observed in liver ferritin from mouse and neonatal pig and were enriched in a low iron fraction of horse spleen ferritin. Based on cyanogen bromide fragmentation and NH2-terminal analysis, the natural and chemically cross-linked subunit dimers had two peptides in common; natural subunit dimers also appeared to have a second region cross-linked, suggesting the possibility of both intra- and intersubunit links in the natural dimers. In sheep spleen ferritin, both heavy and light subunits appeared to participate in subunit dimerization. Natural subunit dimers were enriched in low iron ferritin fractions of all ferritin preparations tested (linear correlation = 0.94) and can explain, at least in part, the previously observed effects of iron core size on the apoferritin shell. Whether the subunit cross-links represent part of the subunit assembly process subsequently cleaved by iron (or copper) or whether the cross-links form after iron core formation in vivo has yet to determined. In either case, it is clear that such post-translational variations can affect iron uptake and release and emphasize the importance of the protein shell in determining the iron storage properties of ferritin.

Amino Acids↗
PubMed1978

Monoclonal IgG anticoagulants delaying fibrin aggregation in two patients with systemic lupus erythematosus (SLE).

There is paucity of information regarding the prolonged plasma thrombin time known to occur in some patients with systemic lupus erythematosus. Detailed investigations of plasma from two such patients disclosed that IgG accounted for this defect in each case. IgG isolated from plasma of either patient possessed the property of delaying fibrin aggregation and prolonging the clotting times of fibrinogen. Preincubation of IgG from either patient with anti-IgG or anti-Fab (rabbit) serum abolished this anticoagulant property. Moreover, the anticoagulant IgG from the first patient was neutralized with anit-k chain and anti-IgG3, that from the second patient with anti-lambda chain and anti-IgG1 serum. These anticoagulants were also dissimilar with respect to their interactions with fibrin(ogen). IgG from the first patient had no anticoagulant activity against fibrin(ogen) species lacking intact Aalpha chains. IgG from the second patient displayed undiminished anticoagulant effect on such fibrin(ogen) species. We conclude that each anticoagulant interacted with a distinct region(s) on the fibrinogen molecule and that these interactions affect or involve sites that participate in the fibrin self-assembly process.

Adolescent↗
PubMedDate not supplied

Self-assembly of fibrin monomer. A light scattering and electron microscopic investigation.

A light scattering method, together with complementary electron microscopy observations, was designed to investigate the self-assembly of fibrin. Calcium-free monomer was used, and clot reconstitution was carried out in solvents corresponding to limit interaction energies of the protein with the medium. The self-assembly process, under physiological conditions, conforms to the following sequence of events. 1) A fast polymerization step leading to linear aggregates. 2) Fiber growth; at this stage onset of the network occurs. 3) Gelation (clot formation). Bound calcium was found to be structurally required for gelation. Its removal results in the formation of thick fibers, which are unable to clot. Evidence is reported favouring our previous hypothesis (Conio et al., 1976) on the onset of the network: branching of linear aggregates is a prerequisite for clotting. The occurrence of a crystallization process, which overlaps to fiber growth, is demonstrated in this paper for the first time. Its dependence on solvent-protein interactions is analyzed. Our results suggest that fibrin monomer is to some extent a flexible molecule. Both flexibility and crystallization may play a functional role in the clotting process in vivo.

Crystallization↗
PubMed1995

RNA structural patterns and splicing: molecular basis for an RNA-based enhancer.

Efficient splicing of the 325-nt yeast (Saccharomyces cerevisiae) rp51b intron requires the presence of two short interacting sequences located 200 nt apart. We used the powerful technique of randomization-selection to probe the overall structure of the intron and to investigate its role in pre-mRNA splicing. We identified a number of alternative RNA-RNA interactions in the intron that promote efficient splicing, and we showed that similar base pairings can also improve splicing efficiency in artificially designed introns. Only a very limited amount of structural information is necessary to create or maintain such a mechanism. Our results suggest that the base pairing contributes transiently to the spliceosome assembly process, most likely by complementing interactions between splicing factors. We propose that splicing enhancement by structure represents a general mechanism operating in large yeast introns that evolutionarily preceded the protein-based splicing enhancers of higher eukaryotes.

Base Sequence↗
PubMed1995

Initial assessment of human gene diversity and expression patterns based upon 83 million nucleotides of cDNA sequence.

In an effort to identify new genes and analyse their expression patterns, 174,472 partial complementary DNA sequences (expressed sequence tags (ESTs)), totalling more than 52 million nucleotides of human DNA sequence, have been generated from 300 cDNA libraries constructed from 37 distinct organs and tissues. These ESTs have been combined with an additional 118,406 ESTs from the database dbEST, for a total of 83 million nucleotides, and treated as a shotgun sequence assembly project. The assembly process yielded 29,599 distinct tentative human consensus (THC) sequences and 58,384 non-overlapping ESTs. Of these 87,983 distinct sequences, 10,214 further characterize previously known genes based on statistically significant similarity to sequences in the available databases; the remainder identify previously unknown genes. Thirty tissues were sampled by over 1,000 ESTs each; only eight genes were matched by ESTs from all 30 tissues, and 227 genes were represented in 20 or more of the tissues sampled with more than 1,000 ESTs. Approximately 40% of identified human genes appear to be associated with basic energy metabolism, cell structure, homeostasis and cell division, 22% with RNA and protein synthesis and processing, and 12% with cell signalling and communication.

Adult↗
PubMed1993

Assembly of GABAA receptor subunits: analysis of transient single-cell expression utilizing a fluorescent substrate/marker gene technique.

GABAA receptor channels (GABARs) composed of varying combinations of alpha 1, beta 1, and gamma 2S subunits were transiently expressed in mammalian cell lines. The whole-cell patch-clamp recording technique was used to determine which combinations of GABAR subunits produced functional receptor channels and whether assembly of GABAR subunits into receptor channels followed a random or preferred sequence. To identify rapidly cells expressing GABARs, mammalian cell lines were cotransfected with combinations of GABAR subunit cDNAs and the Escherichia coli beta-galactosidase gene as a transfection marker. Positively transfected cells were identified by staining with the enzyme substrate fluorescein di-beta-galactopyranoside. Using this technique, we confirmed that functional alpha 1 beta 1 and alpha 1 beta 1 gamma 2S GABARs were assembled in transfected mouse L929 fibroblast cells, but surprisingly, functional alpha 1 gamma 2S and beta 1 gamma 2S GABARs were not expressed. It was determined that after transient transfection, levels of expressed receptors varied little among individual cells permitting comparison of absolute whole-cell GABA-evoked current values. Whole-cell currents recorded from cells coexpressing alpha 1 beta 1 gamma 2S subunits were three to four times larger than those recorded from cells coexpressing alpha 1 beta 1 subunits, and they were always enhanced by coapplied diazepam. The increase in whole-cell current was due in part to the larger single-channel current of the alpha 1 beta 1 gamma 2S GABARs. GABARs comprised of alpha 1 beta 1 gamma 2S subunits were formed preferentially over GABARs of alpha 1 beta 1 subunits alone, since only after substantially increasing the ratio of the beta 1 expression vector over the alpha 1 and gamma 2S subunit expression vectors were alpha 1 beta 1 GABARs formed in the presence of the gamma 2S subunit. These findings suggest that assembly of GABARs from constituent subunits did not proceed randomly to form all possible combinations, but that certain subunit combinations were preferred intermediates during the assembly process.

Animals↗