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At least 757 records · Page 42Linked to original sources
PubMed1997

Role of ribosomes in reinitiation of membrane insertion of internal transmembrane segments in a polytopic membrane protein.

The topogenesis of membrane proteins with a single transmembrane (TM) segment is well understood. However, understanding the topogenesis and membrane assembly of membrane proteins with multiple TM segments (polytopic) is still incomplete. Recently, several studies on P-glycoprotein (Pgp) suggested that the topogenesis of polytopic membrane proteins is likely more complicated than anticipated. While studying the mechanism by which Pgp topogenesis is determined, we unexpectedly found that ribosomes or proteins associated with ribosomes are involved in regulating the membrane insertion and folding of Pgp during its translation. We discovered that when Pgp was translated by wheat germ ribosomes in vitro, TM3 could not reinitiate the insertion of the protein into microsomal membranes following the membrane insertion of TM1 and TM2. In contrast, TM3 could reinitiate membrane insertion when the protein was translated by rabbit reticulocyte ribosomes. These findings suggest that ribosomes or proteins associated with ribosomes play an important role in membrane insertion and folding of TM segments of Pgp and that rabbit reticulocyte and wheat germ ribosomes may use different mechanisms to control the membrane insertion of the same nascent peptide. We propose that ribosomes or proteins associated with ribosomes help reinitiate insertion of internal TM segments into the membrane by dissociation and reassociation with the protein-conducting channel in ER membranes.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Evidence for multiple mechanisms for membrane binding and integration via carboxyl-terminal insertion sequences.

Subcellular localization of proteins with carboxyl-terminal insertion sequences requires the molecule be both targeted to and integrated into the correct membrane. The mechanism of membrane integration of cytochrome b5 has been shown to be promiscuous, spontaneous, nonsaturable, and independent of membrane proteins. Thus endoplasmic reticulum localization for cytochrome b5 depends primarily on accurate targeting to the appropriate membrane. Here direct comparison of this mechanism with that of three other proteins integrated into membranes via carboxyl-terminal insertion sequences [vesicle-associated membrane protein 1(Vamp1), polyomavirus middle-T antigen, and Bcl-2] revealed that, unlike cytochrome b5, membrane selectivity for these molecules is conferred at least in part by the mechanisms of membrane integration. Bcl-2 membrane integration was similar to that of cytochrome b5 except that insertion into lipid vesicles was inefficient. Unlike cytochrome b5 and Bcl-2, Vamp1 binding to canine pancreatic microsomes was saturable, ATP-dependent, and abolished by mild trypsin treatment of microsomes. Surprisingly, although the insertion sequence of polyomavirus middle-T antigen was sufficient to mediate electrostatic binding to membranes, binding did not lead to integration into the bilayer. Together these results demonstrate that there are at least two different mechanisms for correct membrane integration of proteins with insertion sequences, one mediated primarily by targeting and one relying on factors in the target membrane to mediate selective integration. Our results also demonstrate that, contrary to expectation, hydrophobicity is not sufficient for insertion sequence-mediated membrane integration. We suggest that the structure of the insertion sequence determines whether or not specific membrane-bound receptor proteins are required for membrane integration.

Adenosine Triphosphate↗
PubMed2005

Acrylonitrile insertion reactions of cationic palladium alkyl complexes.

The reactions of acrylonitrile (AN) with "L(2)PdMe+" species were investigated; (L(2) = CH(2)(N-Me-imidazol-2-yl)(2) (a, bim), (p-tolyl)(3)CCH(N-Me-imidazol-2-yl)(2) (b, Tbim), CH(2)(5-Me-2-pyridyl)(2) (c, CH(2)py'(2)), 4,4'-Me(2)-2,2'-bipyridine (d), 4,4'-(t)Bu(2)-2,2'-bipyridine (e), (2,6-(i)Pr(2)-C(6)H(3))N=CMeCMe=N(2,6-(i)Pr(2)-C(6)H(3)) (f)). [L(2)PdMe(NMe(2)Ph)][B(C(6)F(5))(4)] (2a-c) and [{L(2)PdMe}(2)(mu-Cl)][B(C(6)F(5))(4)] (2d-f) react with AN to form N-bound adducts L(2)Pd(Me)(NCCH=CH(2))(+) (3a-f). 3a-e undergo 2,1 insertion to yield L(2)Pd{CH(CN)Et}+, which form aggregates [L(2)Pd{CH(CN)Et}](n)(n)(+) (n = 1-3, 4a-e) in which the Pd units are proposed to be linked by PdCHEtCN- - -Pd bridges. 3f does not insert AN at 23 degrees C. 4a-e were characterized by NMR, ESI-MS, IR and derivatization to L(2)Pd{CH(CN)Et}(PR(3))+ (R = Ph (5a-e), Me (6a-c)). 4a,b react with CO to form L(2)Pd{CH(CN)Et}(CO)+ (7a,b). 7a reacts with CO by slow reversible insertion to yield (bim)Pd{C(=O)CH(CN)Et}(CO)+ (8a). 4a-e do not react with ethylene. (Tbim)PdMe+ coordinates AN more weakly than ethylene, and AN insertion of 3b is slower than ethylene insertion of (Tbim)Pd(Me)(CH(2)=CH(2))(+) (10b). These results show that most important obstacles to insertion polymerization or copolymerization of AN using L(2)PdR+ catalysts are the tendency of L(2)Pd{CH(CN)CH(2)R}+ species to aggregate, which competes with monomer coordination, and the low insertion reactivity of L(2)Pd{CH(CN)CH(2)R}(substrate)+ species.

Journal Article↗
PubMed2005

Changes in electronic structure upon lithium insertion into the A-site deficient perovskite type oxides (Li,La)TiO3.

Investigation on variation of the electronic structure accompanying the electrochemical lithium insertion into the perovskite type oxide, (Li,La)TiO3, has been carried out by X-ray absorption spectroscopy (XAS). During the electrochemical lithium insertion, titanium ion reduced its oxidation state from Ti4+ to Ti3+, while La3+ does not contribute to the reduction reaction resulting from Ti K-edge and La L3-edge XAS, respectively. Furthermore, O K-edge XAS showed marked spectral changes with electrochemical lithium insertion, indicating the electronic structure around oxide ion affected by lithium insertion reaction. From the XAS measurement, we have concluded the variation observed in O K-edge XAS was related to the strong interaction with inserted Li ion. To confirm this, first-principles band calculations were performed for the perovskite structure before and after electrochemical lithium insertion. The calculated results showed that the electron originated from inserted Li transferred to neighboring oxide ion locally as well as to Ti ion. This may be due to local neutralization effect of Li to reduce the electrostatic interaction in the crystal.

Journal Article↗
PubMed2002

Study of beta-amyloid peptide (Abeta40) insertion into phospholipid membranes using monolayer technique.

beta-Amyloid peptide (Abeta), a normal constituent of neuronal and non-neuronal cells, has been proved to be the major component of extracellular plaque of Alzheimer's disease (AD). The interaction of Abeta with lipid membranes may be essential for its neurotoxicity. Our previous study revealed that membrane insertion may provide a possible pathway by which Abeta prevents itself from aggregation and fibril formation. In the present work we studied the membrane insertion of Abeta and the factors that affect its insertion ability using a monolayer approach. The results show that Abeta is surface active and can insert into lipid monolayers. When a high level of cholesterol is present, Abeta40 can insert into the phospholipid mixtures simulating physiological membrane composition. Acidic pH enhances Abeta insertion, while the effect of ionic strength is rather complex. Abeta insertion ability may be ultimately relative to cholesterol-rich domains in the monolayers, which indicates strong interaction between Abeta and cholesterol.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2000

Subgingival polishing with a teflon-coated sonic scaler insert in comparison to conventional instruments as assessed on extracted teeth. (I) Residual deposits.

BACKGROUND: Recent studies have shown that endotoxins are located on the periodontally diseased root cementum and not within it. These studies led to the suggestion that the root surface could be treated less aggressively during periodontal therapy. Thus, we designed a teflon-tubed sonic scaler insert for subgingival polishing. It was our objective to assess to which extent this new instrument is capable of removing bacterial deposits in deep pockets in comparison with conventional scaling instruments. METHOD: We compared the extent to which plaque and calculus could be removed with a curette, a conventional sonic and ultrasonic scaler insert, a Per-io-tor insert, and a teflon-tubed sonic scaler insert. 84 teeth requiring extraction had been treated with one of these instruments. After extraction, the teeth were stained with Malachite green, and the following areas were assessed: area lacking plaque and calculus, calculus, and area only covered with plaque. For statistical comparison, nonparametric analyses were carried out. RESULTS: Curettes and conventional ultrasonic and sonic-scaler inserts had more area lacking plaque and calculus (97.5%, 92.2%, 92.1%) than did the Per-io-tor (80.1%) or the teflon-coated sonic scaler insert (84.4%). A similar effectivity sequence was observed for residual soft deposits (curette: 1.9%, ultrasonic scaler: 6.1%, sonic scaler: 5.4%, teflon-coated sonic scaler: 5.1% and Per-io-tor: 9.5%). CONCLUSIONS: The Per-io-tor and the teflon-coated sonic scaler insert seem to be suitable for the removal of soft deposits on the root surface, but not for the removal of calculus.

Adolescent↗
PubMed1992

Insertion of isolated insulin receptors into placental membrane vesicles.

Purified human insulin receptors were inserted into placental plasma-membrane vesicles by fusion of membranes with receptor-lysophosphatidylcholine micelles. Scatchard analysis of insulin binding showed that about 10-15% of the added receptors became inserted into the membrane. The receptor number could be increased about 3-fold, corresponding to approx. 5 pmol of receptor/mg of membrane protein. The receptors became firmly bound to the membrane, as they could not be removed by extensive wash. The insertion of exogenous receptors could be demonstrated by immunoblotting. The inserted insulin receptor had the same insulin-binding affinity as the isolated receptor and the endogenous receptor of the membrane. Insulin binding in the presence or absence of Triton X-100 revealed that more than 80% of the exogenous receptors had a right-side-out orientation. Function of the inserted receptors, as observed by insulin-stimulated autophosphorylation, could be demonstrated. About 80% of the added lysophospholipid, corresponding to approx. 160 nmol of lysophospholipid/mg of membrane protein, became integrated into the membrane and was partly metabolized to phospholipid and to non-esterified fatty acid. The method of insertion of isolated insulin receptors using the natural detergent, lysophospholipid, may be a method for insertion of receptors into intact cells, where the lysophospholipid, as in the plasma-membrane vesicles, will be acylated to phospholipid.

Cell Membrane↗
PubMed2003

Laryngeal mask insertion in children: a rational approach.

BACKGROUND: Various techniques of laryngeal mask airway (LMATM) insertion have been described in adults but only limited clinical trials have been conducted in children despite a varying range in success rate by the recommended method. METHOD: The study was conducted in 62 ASA 1 and 2 children who were randomly allocated for the evaluation of LMA insertion by the midline approach with the cuff completely deflated (group MD, control group, n = 31) or laterally with the cuff partially inflated (group LP, study group, n = 31). Propofol was used as the sole induction agent in all children. Ease of insertion, position of the LMA with fibreoptic laryngoscope and incidence of stomach insufflation were assessed. RESULTS: Fewer attempts and a significant reduction in the time for insertion was noted in group LP (14.4 +/- 4.2 s) compared with group MD (23.1 +/- 2.1 s), P < 0.05. Despite a good seal around the cuff and satisfactory ventilation a significantly higher incidence of malposition of the LMA was recorded by intraluminal fibreoptic endoscopy in group MD (13% to nil), P < 0.05. Similarly gastric insufflation was significantly greater in group MD (42% compared with 10%). In children with grade 3 fibreoptic view significantly higher endtidal carbon dioxide values were recorded throughout the study period after LMA insertion until its removal. LMA was stained with blood in 13% children in group MD compared with 3% in group LP at the time of removal. CONCLUSION: A partially inflated cuff inserted by the lateral route is a better method of insertion in children and grade 3 fibreoptic views can be associated with a significant build up of carbon dioxide in children breathing spontaneously.

Anesthesiology↗
PubMedDate not supplied

Extrusion of metal radiological marker from a total ankle replacement insert: a case report.

Total ankle arthroplasty has become an increasingly performed procedure for the treatment of ankle arthritis. Failures related to polyethylene inserts can result from uncorrected deformities or malalignment of the components. We report a case of a 63-year-old man who underwent total ankle arthroplasty for osteoarthritis of the ankle. The talar component was placed in neutral alignment. Initial postoperative recovery and rehabilitation were unremarkable. At 9 months postoperatively, plain radiographs of the ankle showed worsening varus tilt when compared with radiographs taken earlier. There was also radiographic evidence of separation of the posterior metal marker, suggestive of a fracture of the polyethylene insert. Revision surgery to correct the varus tilt and replace the polyethylene insert was performed. At operation, the polyethylene insert was found to be intact with no evidence of fracture. The posterior metal marker of the polyethylene insert was found to be extruded from the insert. Small degrees of ankle prosthesis malalignment can lead to various degrees of polyethylene liner failure, such as metal marker extrusion. This article also shows that these metal markers may not be accurate indicators of the integrity of the polyethylene insert.

Ankle Joint↗
PubMed2002

Predicting the depth of insertion of left-sided double-lumen endobronchial tubes.

OBJECTIVE: To analyze the parameters that predict the depth of insertion of a left-sided double-lumen tube (DLT) and to assess the accuracy of the parameters after intubation. DESIGN: Prospective. SETTING: Tertiary-care hospital. PARTICIPANTS: Patients undergoing 1-lung ventilation for thoracic surgery (n = 240). INTERVENTIONS: In the first 121 patients, the ideal depth of insertion was verified using fiberoptic bronchoscopy in the lateral position. Multiple regression analysis was used to find the correlation of this depth of insertion to the patients' height, weight, age, and the clavicular-to-carinal distance of the trachea measured from the chest radiograph. Another 119 patients were studied in whom the DLT was inserted blindly using the best regression line. The accuracy of the technique was assessed by fiberoptic bronchoscopy. MEASUREMENTS AND MAIN RESULTS: The depth of DLT insertion correlated significantly (p < 0.05) only with the height and clavicular-to-carinal distance of the trachea of the patients with the best regression line: Depth of insertion (cm) = 0.75 x clavicular-to-carinal distance of trachea (cm) + 0.112 x height (cm) + 6 with R(2) = 0.62 and p < 0.001. Using this best regression line, the DLT was placed in an acceptable position in 93 patients in the lateral position (positive predictive value of 78.2%) without further intraoperative adjustments. CONCLUSION: The ideal depth of insertion of the left-sided DLT correlated significantly with patients' height and clavicular-to-carinal distance of the trachea. The best regression line enabled the left-sided DLT to be placed in an acceptable position without complications nearly 80% of the time.

Adult↗
PubMed2000

Examination of the anatomic relationship of the proximal germinal nail matrix to the extensor tendon insertion.

The purpose of this study was to delineate the relationship of the terminal extensor tendon insertion to the proximal limit of the germinal nail matrix. Sixteen fresh-frozen human cadaver fingers without any evidence of trauma (average age, 55 years; 3 males and 1 female) were used for this study. Under x25 magnification the proximal limit of the germinal nail matrix and the terminal bony insertion of the extensor tendon were identified. The distance from the terminal tendon insertion to the germinal nail matrix was ascertained using precision calipers. The average distance from the terminal extensor tendon insertion to the proximal edge of the germinal nail matrix was found to be 1.2 mm. We conclude that the proximal limit of the germinal matrix is extremely close to the terminal extensor tendon bony insertion. When the extensor tendon insertion is visualized during operative exposures of the dorsum of the distal phalanx, care should be taken to avoid damaging the germinal matrix. Conversely, when the nail bed is being completely excised, visualization of the insertion of the extensor tendon will indicate that further proximal dissection is not required.

Adolescent↗
PubMed2002

Does the insertion depth in push enteroscopy depend on the working length of the enteroscope?

BACKGROUND AND STUDY AIMS: Using push enteroscopy, the small bowel can only be investigated in part. This preliminary prospective randomized study examined whether increasing the length of the enteroscope can have a beneficial effect on the insertion depth. PATIENTS AND METHODS: Between August 1999 and December 1999, 28 consecutive patients were investigated using push enteroscopy and were randomly assigned to two groups. One group was investigated using the Olympus push enteroscope SIF-100 (working length 2200 mm). In the other group, the Olympus push enteroscope SIF-Q140 (working length 2500 mm) was used. All investigations were carried out using an overtube. The insertion depth was estimated by counting the folds in the small bowel. In addition, the insertion length was estimated in centimeters by withdrawing the instrument to the pylorus after straightening. RESULTS: The two groups were comparable in terms of age, sex distribution, indication for enteroscopy, investigation time, and pathological findings. There were no significant differences in the insertion length between the two types of instrument. With the SIF-100, the median number of folds was 95 (range 30 - 213) and the insertion length was 72.5 cm (range 40 - 110 cm); and with the SIF-Q140, the median number of folds was 79 (range 18 - 203) and the insertion length was 70.0 cm (range 20 - 140 cm). CONCLUSIONS: As there was no significant difference in the insertion depth between the shorter instrument (Olympus SIF-100) and the longer one (Olympus SIF-Q140), it can be concluded from this preliminary study that there is no advantage in using a longer enteroscope. To document a significant difference, further studies with a larger numbers of patients would be necessary.

Adult↗
PubMed2004

[Evaluation of the insertion-trauma of the Nucleus Contour Advance electrode-array in a human temporal bone model].

BACKGROUND: The development of intracochlear electrode arrays is aiming at a placement close to the modiolus with an insertion as atraumatic as possible. A new perimodiolar electrode model the Nucleus Contour Advance was to be evaluated regarding the possible intracochlear trauma. METHODS: The implantation of the Contour Advance electrode was performed in 11 frozen native temporal bones. Beneath a regular insertion in 5 temporal bones in 6 cases the insertion was carried out using the "advance-off-stylett" technique with a fixed stylett. The temporal bones were embedded in metacrylate based resin for histomorphological evaluation. The evaluation was performed regarding to the intracochlear placement close to the modiolus and the damage to intracochlear fine structures (basilar membrane, osseus spiral lamina). RESULTS: In 2 out of 11 cases we found a perforation from the scala tympani to the scala vestibuli independent of the insertion-technique. A severe intracochlear trauma was observed in one case with fracture of osseus spiral lamina using the AOS-technique. A close position to the modiolus could be achieved by insertion the scala tympani without perforation of the basilar membrane. CONCLUSIONS: The Nucleus Contour Advance electrode array showed minimal trauma in human temporal bones by using a standard insertion technique. By using the freehand AOS-technique a severe cochlear trauma is possible. Therefore further development in electrode design and the use of an insertion-tool is recommended.

Basilar Membrane↗
PubMed2005

[The influence of insertion depth on the preservation of residual hearing after cochlear implantation].

BACKGROUND: Cochlear implantation may be indicated in patients with bilateral severe sensory hearing loss. Patients with minimal residual hearing have more benefit from cochlear implantation than from optimal fitted hearing aids. However, it has to be considered that inner ear structures might be damaged during electrode insertion. METHODS: We analysed the influence of insertion depth on the preservation of residual hearing in 47 cochlear implant patients (type of implant: Nucleus 22 M or 24 M) by using the pure tone audiometry. Frequency-specific analyses of pre- and postoperative audiograms on the implanted side were performed, evaluating only frequencies above 500 Hz. The insertion depth was documented by stiffening rings outside the cochlea. RESULTS: Residual hearing was more obtained in cases with complete insertion of the electrode array than in those cases with incomplete insertion. In the frequencies 1000 and 4000 Hz these results are significant. CONCLUSION: In our opinion, the perceived resistance producing intracochlear damages and preventing the complete electrode-insertion at the same time is an explanation for the significantly poorer results of the patients with incomplete insertion.

Audiometry, Pure-Tone↗
PubMed2002

Homologous recombination at the border: insertion-deletions and the trapping of foreign DNA in Streptococcus pneumoniae.

Integration of foreign DNA was observed in the Gram-positive human pathogen Streptococcus pneumoniae (pneumococcus) after transformation with DNA from a recombinant Escherichia coli bacteriophage lamda carrying a pneumococcal insert. Segments of lamda DNA replaced chromosomal sequences adjacent to the region homologous with the pneumococcal insert, whence the name insertion-deletion. Here we report that a pneumococcal insert was absolutely required for insertion-deletion formation, but could be as short as 153 bp; that the sizes of foreign DNA insertions (289-2,474 bp) and concomitant chromosomal deletions (45-1,485 bp) were not obviously correlated; that novel joints clustered preferentially within segments of high GC content; and that the crossovers in 29 independent novel joints were located 1 bp from the border or within short (3-10 nt long) stretches of identity (microhomology) between resident and foreign DNA. The data are consistent with a model in which the insert serving as a homologous recombination anchor favors interaction and subsequent illegitimate recombination events at microhomologies between foreign and resident sequences. The potential of homology- directed illegitimate recombination for genome evolution was illustrated by the trapping of functional heterologous genes.

Bacterial Proteins↗
PubMed2005

An algorithm for progressive multiple alignment of sequences with insertions.

Dynamic programming algorithms guarantee to find the optimal alignment between two sequences. For more than a few sequences, exact algorithms become computationally impractical, and progressive algorithms iterating pairwise alignments are widely used. These heuristic methods have a serious drawback because pairwise algorithms do not differentiate insertions from deletions and end up penalizing single insertion events multiple times. Such an unrealistically high penalty for insertions typically results in overmatching of sequences and an underestimation of the number of insertion events. We describe a modification of the traditional alignment algorithm that can distinguish insertion from deletion and avoid repeated penalization of insertions and illustrate this method with a pair hidden Markov model that uses an evolutionary scoring function. In comparison with a traditional progressive alignment method, our algorithm infers a greater number of insertion events and creates gaps that are phylogenetically consistent but spatially less concentrated. Our results suggest that some insertion/deletion "hot spots" may actually be artifacts of traditional alignment algorithms.

Algorithms↗
PubMed1992

Tn10 insertion specificity is strongly dependent upon sequences immediately adjacent to the target-site consensus sequence.

Transposon Tn10 inserts preferentially into particular "hotspots" that have been shown by sequence analysis to contain the symmetrical consensus sequence 5'-GCTNAGC-3'. This consensus is necessary but not sufficient to determine insertion specificity. We have mutagenized a known hotspot to identify other determinants for insertion into this site. This genetic dissection of the sequence context of a protein binding site shows that a second major determinant for Tn10 insertion specificity is contributed by the 6-9 base pairs that flank each end of the consensus sequence. Variations in these context base pairs can confer variations of at least 1000-fold in insertion frequency. There is no discernible consensus sequence for the context determinant, suggesting that sequence-specific protein-DNA contacts are not playing a major role. Taken together with previous work, the observations presented suggest a model for the interaction of transposase with the insertion site: symmetrically disposed subunits bind with specific contacts to the major groove of consensus-sequence base pairs, while flanking sequences influence the interaction through effects on DNA helix structure. We also show that the determinants important for insertion into a site are not important for transposition out of that site.

Base Sequence↗
PubMed1994

African origin of human-specific polymorphic Alu insertions.

Alu elements are a family of interspersed repeats that have mobilized throughout primate genomes by retroposition from a few "master" genes. Among the 500,000 Alu elements in the human genome are members of the human-specific subfamily that are not fixed in the human species; that is, not all chromosomes carry an Alu element at a particular locus. Four such polymorphic human-specific Alu insertions were analyzed by a rapid, PCR-based assay that uses primers that flank the insertion point to determine genotypes based on the presence or absence of the Alu element. These four polymorphic Alu insertions were shown to be absent from the genomes of a number of nonhuman primates, consistent with their arising as human genetic polymorphisms sometime after the human/African ape divergence. Analysis of 664 unrelated individuals from 16 population groups from around the world revealed substantial levels of variation within population groups and significant genetic differentiation among groups. No significant associations were found among the four loci, consistent with their location on different chromosomes. A maximum-likelihood tree of population relationships showed four major groupings consisting of Africa, Europe, Asia/Americas, and Australia/New Guinea, which is concordant with similar trees based on other loci. A particularly useful feature of the polymorphic Alu insertions is that the ancestral state is known to be the absence of the Alu element, and the presence of the Alu element at a particular chromosomal site reflects a single, unique event in human evolution. A hypothetical ancestral group can then be included in the tree analysis, with the frequency of each insertion set to zero. The ancestral group connected to the maximum-likelihood tree within the African branch, which suggests an African origin of these polymorphic Alu insertions. These data are concordant with other diverse data sets, which lends further support to the recent African origin hypothesis for modern humans. Polymorphic Alu insertions represent a source of genetic variation for studying human population structure and evolution.

Africa↗