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Biomedical subjects

I Nilsson

Publications and source records attributed to I Nilsson.

At least 91 records · Page 5Linked to original sources
PubMed1994

De novo design of integral membrane proteins.

We have designed integral membrane proteins with one, two and four hydrophobic transmembrane segments of highly simplified amino acid composition and with appropriately placed positively charged lysine residues intended to control the overall membrane orientation. When expressed in Escherichia coli, these model proteins insert efficiently into the inner membrane and adopt the predicted topologies. This demonstrates the feasibility of de novo design of multi-spanning integral membrane proteins, and opens up new possibilities for membrane protein engineering.

Amino Acid Sequence↗
PubMed1994

The COOH-terminal ends of internal signal and signal-anchor sequences are positioned differently in the ER translocase.

Signal peptides (SPs) target proteins to the secretory pathway and are cleaved from the nascent chain once the translocase in the ER has been engaged. Signal-anchor (SA) sequences also interact transiently with the ER translocase, but are not cleaved and move laterally out of the translocase to become permanent membrane anchors. One obvious difference between SP and SA sequences is the considerably longer hydrophobic regions (h regions) of the latter. To study the interaction between SP/SA sequences and the ER translocase, we have constructed signal sequences with poly-Leu h regions ranging in length from 8 to 29 residues and have characterized their locations within the translocase using both a new assay that measures the minimum number of amino acids needed to span the distance between the COOH-terminal end of the h region and the active site of the oligosaccharyl transferase enzyme and an assay where the efficiency of signal peptidase catalyzed cleavage is measured. Our results suggest that SP and SA sequences are positioned differently in the ER translocase.

Amino Acid Sequence↗
PubMed1993

Positively charged amino acids placed next to a signal sequence block protein translocation more efficiently in Escherichia coli than in mammalian microsomes.

Positively charged amino acids are known efficiently to block protein secretion in Escherichia coli, when placed within a short distance downstream of a signal sequence. It is not known whether the same applies to protein secretion in eukaryotic cells, though statistical studies of signal sequences of prokaryotic and eukaryotic secretory proteins have suggested that the situation may be different in this case. Here, we show that identical charge mutations in a model protein have different effects on membrane translocation in E. coli and in mammalian microsomes, and that the 'charge block' effect is much more pronounced in the prokaryotic system. This finding has implications not only for our understanding of the mechanisms of protein secretion, but also points to a potential problem in the expression of eukaryotic secretory proteins in bacteria.

Amino Acid Sequence↗
PubMed1993

Changes in the ovarian intermediate filament desmin during the luteal phase of the adult pseudopregnant rat.

The occurrence of the intermediate filament desmin in ovary and corpus luteum of pseudopregnant rats was studied using Western blot analysis and immunohistochemistry. The luteal phase was induced by mating with vasectomized male rats and ovaries were studied after 6, 11 and 19 days. The findings from the Western blot analysis showed that desmin was present in the corpus luteum. Immunohistochemical localization of desmin showed two types of localization in the corpus luteum. The arteries around the corpus luteum, as well as arteries elsewhere in the ovary, had a high content of desmin in their muscle layer. Dispersed in the corpus luteum was an immunohistochemical staining of desmin that was localized mainly adjacent to the luteal cells. In the other part of the ovary a weak staining was registered in the theca layer, no staining in the granulosa layer and a streaky staining in the hilar region of the ovary. Desmin filaments are found in muscle cells of all types, including vascular smooth muscle cells. Probably, all desmin in the ovary is localized to smooth muscle cells with the possible exception of the corpus luteum where very few muscle cells have been identified. Localization to other vascular cells as endothelial is possible. In this study we found an increase in desmin content in the corpus luteum after day 6. If desmin is related to vascular resistance, our finding is consistent with the decrease in blood flow that occurs after day 6.

Animals↗
PubMed1993

Pancreaticobiliary juice releases motilin during phase I of the migrating motor complex in man.

The effect of duodenal perfusion with pancreaticobiliary juice on plasma motilin was investigated in eight fasting subjects. The study was undertaken with recording of gastrointestinal motility, to predict spontaneous fluctuations in plasma motilin levels. Duodenal perfusion with pancreaticobiliary juice or saline at a rate of 5 ml/min for 10 min was performed in random order after the second or third activity front. The 30-min integrated plasma motilin response was significantly greater after perfusion with pancreaticobiliary juice: 1.5 (0.7-2.3) nmol x min/l (mean and 95% confidence interval), compared with 1.0 (0.5-1.5) nmol x min/l after saline (p < 0.05). Although perfusion with pancreaticobiliary juice was followed by endogenous plasma motilin peaks after about 20 min in six of eight subjects, the mean interval to the next activity front was not significantly different. In conclusion, duodenal perfusion with pancreaticobiliary juice in phase I of the migrating motor complex releases plasma motilin without affecting the fasting motility pattern.

Adult↗
PubMed1992

A signal peptide with a proline next to the cleavage site inhibits leader peptidase when present in a sec-independent protein.

Proline residues are rarely found in the three most C-terminal positions of bacterial signal peptides, and have never been found in position +1 immediately following the cleavage site. It was recently shown that a Pro+1 mutation in the E. coli maltose binding protein precursor not only prevents cleavage of the signal peptide but also inhibits the leader peptidase enzyme, resulting in cessation of cell growth (Barkocy-Gallagher, G.A. and Bassford, P.J. (1992) J. Biol. Chem. (in press)). Since maltose binding protein is dependent on the sec machinery for translocation across the inner membrane, it was not clear if this 'Pro+1' effect was restricted to sec-dependent proteins, or whether it applies also to proteins that do not require the sec functions for translocation. We now present data suggesting that the striking phenotypic effects of Pro+1 mutations can be elicited also by sec-independent proteins.

Amino Acid Sequence↗
PubMed1992

Telescopic suction tube for microsurgery.

An adjustable telescopic suction tube has been developed for microsurgery. Owing to this innovation, the surgeon can easily set the suction tube to a suitable length by gently pulling the end of the telescopic tube out or in.

Equipment Design↗
PubMed1992

Cell surface proteins of Helicobacter pylori as antigens in an ELISA and a comparison with three commercial ELISA.

Cell surface proteins of Helicobacter pylori were solubilized by extraction with acidic glycine buffer, N-octyl-glucoside, lithium chloride, and distilled water, and by sonication. The preparations were evaluated as antigens in ELISA to detect serum IgG responses in patients and healthy subjects. SDS-PAGE analyses of the preparations from a type strain (NCTC 11637) and of acidic glycine extracts of 4 clinical isolates showed multiple protein bands. The sera were classified as HP+ve and HP-ve by culture of biopsy and immunoblotting. Sera were considered positive for H. pylori if they detected the specific 120kD antigen or 4-5 other bands. 49 sera were HP+ve; the 51 HP-ve sera did not react in immunoblotting. 35/44 sera (80%) that reacted with the 120kD antigen demonstrated high titers in ELISA with all antigen preparations, and the remaining 9(20%) sera gave discordant results. 4/5 HP+ve sera that did not react with the 120kD antigen, demonstrated high ELISA titers with all 5 antigen preparations. Glycine extracts of 3 isolates did not exhibit the 120kD protein, but were equally sensitive in ELISA. The role of 120kD antigen in our ELISA was not clear. Immunoblotting demonstrated that the 5 antigen preparations share similar antigenic components. All preparations were similarly high in sensitivity and specificity, indicating that surface antigens could be satisfactorily used in our ELISA. Our ELISA using the glycine extract was compared with commercial H. pylori ELISAs developed by Bio-Rad Laboratories, USA (GAP ELISA), Roche, Switzerland (EIA 2G), and Whittaker Bioproducts, USA (Pyloristat).(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Bacterial↗
PubMed1991

A de novo designed signal peptide cleavage cassette functions in vivo.

Leader peptidase (Lep) is a membrane-bound enzyme of the Escherichia coli inner membrane that serves to remove signal peptides from exported proteins. Statistical and experimental studies of known signal peptides have defined a short C-terminal region that seems to provide the information for correct cleavage by Lep. Based on the patterns of conserved amino acids found in this region, we have designed a signal peptide "cleavage cassette." This cassette is processed at the expected site when introduced after an uncleaved signal peptide. Furthermore, processing is blocked in the predicted manner when the (-3, -1)-rule for signal peptide cleavage is violated. This suggests that current understanding of the sequence requirements for signal peptide cleavage is sufficiently advanced to be used in, e.g. protein engineering applications.

Amino Acid Sequence↗
PubMed1991

Effects of direct current on renal function. An experimental study in pigs.

Electric current from an external source was introduced between electrodes operatively placed into the ureters and positioned in the renal pelves of 13 pigs. Urinary excretion via the cathodic kidney showed a marked increase. The renal plasma flow and glomerular filtration rate diminished with increasing voltage, but no significant difference was found between the cathodic and the anodic kidney. The fractional sodium excretion by the cathodic kidney was 80% higher, indicating that the electric current mainly affected tubular function. A possible clinical application for electric fields in the kidneys is discussed.

Animals↗
PubMed1991

The sociomoral reflection measure: applicability to Swedish children and adolescents.

The Sociomoral Reflection Measure (SRM; Gibbs & Widaman, 1982) was developed as a group administerable instrument for measuring developmental stages of moral reasoning. The aim of this study was to examine its reliability and construct validity, employing a sample of 542 Swedish elementary and high school students (aged 8-17), from schools within metropolitan Stockholm. Interrater reliability varied between 0.83 and 0.92, and the internal consistency coefficient was 0.76. Factor analyses of the norms (on which the overall score is based) revealed one factor for the oldest age group (16-17 years), but two factors among the younger subjects (8-15 years), clearly separating the norms related to each of the two moral dilemmas. The Sociomoral Reflection Maturity Score was moderately, but significantly, related to both age and grade. The results suggests that, although used in a non-American context and with self-trained raters, the SRM seems highly applicable in Sweden, at least for research purposes.

Adolescent↗
PubMed1990

Cis-trans isomerization of an angiotensin I-converting enzyme inhibitor. An enzyme kinetic and nuclear magnetic resonance study.

The angiotensin I-converting enzyme (peptidyl-dipeptide hydrolase, EC 3.4.15.1) inhibitor, ramiprilat (2-[N-[(S)-1-ethoxycarbonyl-3-phenylpropyl]-L-Ala]-(1S,3S,5S)-2- azabicyclo[3.3.0]octane-3-carboxylic acid), is shown to exist in tow conformational isomers, cis and trans, which interconvert around the amide bond. The two conformers were separated by reversed-phase high-performance liquid chromatography. The conformers were identified by nuclear Overhauser effect measurements. From line shape analysis the isomerization rate constants were determined to be kcis----trans = 15 s-1 and ktrans----cis = 5 s-1 at 368 K in [2H]phosphate buffer (p2H 7.5). By enzyme kinetic studies using 3-(2-furylacryloyl)-L-Phe-Gly-Gly as substrate, the trans conformer was found to be the most potent enzyme inhibitor, whereas the cis conformer had a very low inhibitory effect. A new inhibition mechanism is presented for this type of slow, tight-binding inhibitors that contain an amide bond. This mechanism involves an equilibrium between the two conformers and the enzyme-bound inhibitor complex.

Angiotensin-Converting Enzyme Inhibitors↗