Biomedical subjects

M Strömqvist

Publications and source records attributed to M Strömqvist.

35 records · Page 2Linked to original sources

PubMed1995

Human milk kappa-casein and inhibition of Helicobacter pylori adhesion to human gastric mucosa.

Readily digested caseins, which account for almost half of the protein content in human milk, are important as nutritional protein for breast-fed infants. It has also been advocated that part of the antimicrobial activity of human milk resides in the caseins, most likely the glycosyated K-casein. Top explore this possibility, we purified K-casein from human milk to homogeneity by a two-step size-exclusion chromatography procedure. Purified human K-casein, in contrast to K-casein purified from bovine milk, effectively inhibited the cell lineage-specific adhesion of fluoroisothiocyanate-labeled Helicobacter pylori to human gastric surface mucous cells. The inhibitory activity was abolished by metaperiodate oxidation and considerably reduced by preincubation with alpha-L-fucosidase but not with alpha-N-acetylneuraminidase or endo-beta-galactosidase. These results strongly support the view that fucose containing carbohydrate moieties of human K-casein are important for inhibition of H. pylori adhesion and, thus, infection. They also suggest that breastfeeding may protect from infection by H. pylori during early life and that species-specific glycosylation patterns, as illustrated by human bovine K-casein, partly determine both the narrow host spectrum of this human gastric pathogen and the capacity to resist infection.

Animals↗

PubMed1994

Cloning, expression, and characterization of stratum corneum chymotryptic enzyme. A skin-specific human serine proteinase.

The cDNA encoding human stratum corneum chymotryptic enzyme (SCCE); an epidermal serine-proteinase which was recently purified from human stratum corneum, was isolated from a keratinocyte derived library. The obtained nucleotide sequence contained an open reading frame sufficient to encode a preproprotein consisting of 253 amino acid residues. Expression of two mRNA species hybridizing with SCCE cDNA, 1.2 and 2.0 kilobases, respectively, was detected to human skin. These two forms differ with respect to the length of the 3'-untranslated sequence. Analysis of mRNA derived from various human tissues showed that abundant expression of the SCCE gene was restricted to human skin. The cloned cDNA was introduced to a bovine papilloma virus-based expression system and recombinant protein was purified and characterized. The results show that recombinant SCCE is produced with a 22-amino acid residue signal peptide and a propeptide of 7 amino acid residues. Tryptic digestion removed this propeptide and yielded a proteolytically active protein with the same NH2-terminal amino acid sequence as native SCCE. The deduced amino acid sequence contains the conserved active site regions of serine proteinases. The calculated molecular mass of unglycosylated active SCCE was 24.4 kDa. The sequence indicates one tentative N-glycosylation site located near the C terminus. Recombinant SCCE was found to be heterogenous regarding glycosylation in a manner similar to that of the native enzyme.

Abdomen↗

PubMed1994

Peptide mapping using combinations of size-exclusion chromatography, reversed-phase chromatography and capillary electrophoresis.

Recombinant extracellular superoxide dismutase was proteolytically degraded by trypsin and the digest was thereafter separated using three different separation techniques. The size differences of the obtained fragments were exploited by size-exclusion chromatography (SEC) on a highly efficient column for peptide separation. Collected fractions representing different size groups of peptides were then separated on the basis of hydrophobicity on reversed-phase liquid chromatography (RPLC). This led to simplified RPLC-chromatograms where collected peaks were considerably more pure than if the digest was separated direct on RPLC and the identity of eluted peaks could easily be determined by amino acid analysis. Finally the digest was run on capillary electrophoresis for separation based on charge differences. For the identification of the different peaks in the electropherogram, the total digest was spiked with known peptides purified by the two other separation techniques. This technique proved to be very powerful for peak identification in an electropherogram from a digest composed of many fragments eluting closely together.

Amino Acid Sequence↗

PubMed1994

Structure of the human beta-casein encoding gene.

The entire human beta-casein-encoding gene, Bca, was cloned and sequenced. The gene consists of eight exons ranging from 21 to 531 nucleotides (nt) in length and extending over 10,466 nt. Exon-2 contains the translational start, the entire signal sequence and the codons for the two first amino acids of the mature protein. This corresponds to the organization found in other species. The translational stop is localized to exon-7. Exon/intron boundaries are in accordance with the AG/GT rule and conform to suggested consensus sequences. Splice junctions are located between coding triplets. In all other species analyzed, Bca has been found to consist of nine exons; however, within intron-2 of the human gene, a sequence omitted from human mRNA, but corresponding to exon-3 of other known Bca genes, was revealed.

Amino Acid Sequence↗

PubMed1994

Expression and characterization of biologically active human extracellular superoxide dismutase in milk of transgenic mice.

We have targeted the expression of recombinant human extracellular superoxide dismutase, a glycosylated tetrameric metalloprotein, to the mammary gland of transgenic mice. This was achieved by using regulatory elements from either the murine whey acidic protein gene or the ovine beta-lactoglobulin gene to control expression of human extracellular superoxide dismutase cDNA. Whey acidic protein regulatory sequences directed high level mammary gland-specific expression of the recombinant gene and secretion of biologically active extracellular superoxide dismutase into the milk. The produced recombinant protein was fully active, it was in tetrameric form, it showed heparin affinity, and its mass was similar to that of the native enzyme. In addition, the in vivo plasma clearance in a rabbit model was similar to the previously studied native and recombinant forms. To our knowledge, this is the first example of efficient production of a tetrameric, protease-susceptible metalloprotein in milk of transgenic animals. Production at equivalent levels in transgenic farm animals would yield sufficient extracellular superoxide dismutase for therapeutic purposes.

Animals↗

PubMed1994

Separation of active and inactive forms of recombinant human plasminogen activator inhibitor type 1 (PAI-1) expressed in Chinese hamster ovary cells: comparison with native human PAI-1.

Human plasminogen activator inhibitor type 1, PAI-1, was expressed in Chinese hamster ovary cells. A production level of 10-15 mg latent PAI-1 per liter of media was achieved after methotrexate amplification. Latent recombinant PAI-1 was purified by two chromatographic steps, cation exchange chromatography on CM-Sepharose and affinity chromatography on heparin-Sepharose. The obtained latent PAI-1 was approximately 90-95% pure showing one homogenous peak upon size-exclusion chromatography. However, four different isoforms due to different degrees of sialylation could be seen upon isoelectric focusing. Purified latent PAI-1 was activated by incubation in 6 M guanidine-HCl. By this method, 40-60% of PAI-1 was converted to an active form after removing the denaturant. The active fraction of PAI-1 was separated from inactive material by size exclusion chromatography on Superdex 200. Active PAI-1 migrated as expected for a 43-kDa large protein, while inactive PAI-1 migrated as larger protein complexes, suggesting that the remaining inactive PAI-1 was in the form of aggregates. This method for the separation of active and inactive PAI-1 could also be used for activated native PAI-1 prepared from human endothelial cells. Active recombinant PAI-1 was remarkably stable at pH 5.5, both when stored on ice and when stored at room temperature.

Amino Acids↗

PubMed1993

Recombinant human milk bile salt-stimulated lipase. Catalytic activity is retained in the absence of glycosylation and the unique proline-rich repeats.

Human milk bile salt-stimulated lipase ensures efficient utilization of triacylglycerol by breast-fed infants. Cloning and sequencing of cDNA have revealed that the peptide chain consists of 722 amino acid residues showing only little homology to typical lipases. The sequence is identical to that of pancreatic carboxylic-ester hydrolase. The COOH-terminal part contains 16 proline-rich repeats of 11 residues with O-linked carbohydrate. The only N-linked sugar chain is situated close to the active-site serine. Using C127 cells and a bovine papilloma virus vector, high and stable expression of full-length lipase and of several variants, obtained by site-directed mutagenesis, was achieved. The produced proteins were purified and further characterized. Variants lacking all, or all but two, repeats were active with similar specific activity and the same bile salt dependence as the native milk enzyme. Changing the asparagine necessary for N-glycosylation gave the same principal results. Active recombinant full-length lipase was also produced in a bacterial system. We conclude that neither glycosylation (N- or O-linked) nor the proline-rich repeats are essential for catalytic activity or bile salt activation of human milk bile salt-stimulated lipase.

Amino Acid Sequence↗

PubMed1993

Characterization of recombinant human extracellular superoxide dismutase.

Recombinant human extracellular superoxide dismutase produced in chinese hamster ovary cells has been characterized using several chromatographic methods. Peptide mapping confirmed the expected primary structure. The 15 amino acids at the N-terminal end were sequenced and were in accordance with expectations in all positions. The C-terminal amino acids have been confirmed both by amino acid composition studies of a peptide of 42 amino acids and by specific sequential cleavage of the last three C-terminal amino acids with carboxypeptidase A. Both methods demonstrated a full length C-terminus. At physiological ionic strength, the dismutase exists for ca. 25% as octamers or larger polymers, and the amount of polymers increases at lower ionic strength.

Amino Acid Sequence↗

PubMed1993

Expression of human milk beta-casein in Escherichia coli: comparison of recombinant protein with native isoforms.

Studies on physiological function and on structure-function relationships of human milk beta-casein have been limited. In this study, we have introduced the human beta-casein cDNA into vectors designed for expression in Escherichia coli. The inducible T7-based expression system resulted in high-level expression of recombinant beta-casein. The recombinant beta-casein, localized intracellularly in E. coli, was purified to homogeneity and compared with purified native beta-casein, in particular with respect to phosphorylation. The E. coli-produced beta-casein was found to comigrate with the full-length, nonphosphorylated native human beta-casein isoform on SDS-PAGE. An N-terminal peptide containing all tentative phosphorylation sites was isolated from the recombinant protein and analyzed by mass spectrometry. The molecular mass as well as the migration of this peptide on reversed-phase chromatography confirmed that it was unphosphorylated.

Amino Acid Sequence↗

PubMed1992

A non-glycosylated extracellular superoxide dismutase variant.

The secretory tetrameric extracellular superoxide dismutase (EC-SOD) is the only glycosylated SOD isoenzyme. The importance of the carbohydrate moiety for the properties of the enzyme is unknown. An expression vector defining nonglycosylated EC-SOD (ngEC-SOD) was constructed by mutagenesis of the codon for Asn-89 into a codon for Gln. The vector was transfected into Chinese hamster ovary DXB-11 cells and ngEC-SOD was isolated to 70% purity from the culture media of selected clones. The absence of glycosylation was established by the lack of affinity for various lectins, the absence of staining with the periodic acid-Schiff reagent, the change in mobility and composition of the tryptic peptide containing the mutated glycosylation site, and the reduction in apparent molecular mass upon SDS/PAGE and size-exclusion chromatography. The tetrameric state was retained. The heparin affinity, a fundamental and distinguishing property of EC-SOD, was found to be slightly increased. The enzymic activity was essentially retained. The major difference from native glycosylated enzyme in physical properties was a marked reduction in solubility. Like glycosylated EC-SOD, ngEC-SOD was, after intravenous injection into rabbits, rapidly sequestered by the vessel endothelium, and was promptly released into plasma after injection of heparin. The only difference from glycosylated EC-SOD in this behaviour, was a slightly more rapid elimination of the mutant enzyme from the vasculature. It is concluded that no specific biological role for the EC-SOD carbohydrate moiety could be revealed.

Animals↗

PubMed1992

Cloning and sequencing of human kappa-casein cDNA.

A cDNA encoding kappa-casein of human milk was cloned and sequenced. The kappa-casein cDNA was isolated from a lambda gt11 library generated from mRNA prepared from a mammary gland biopsy obtained from a lactating woman. The library was screened with polyclonal rabbit antibodies raised against purified native kappa-casein. The obtained nucleotide sequence contained an ORF sufficient to encode the entire amino acid sequence of a kappa-casein precursor protein consisting of 182 amino acids. This includes a tentative signal peptide of 20 amino acids and a processed protein of 162 amino acids.

Amino Acid Sequence↗

PubMed1992

Periodic acid/Schiff staining of glycoproteins immobilized on a blotting matrix.

A simple and sensitive method for the detection of glycoproteins and glycopeptides in solution and in polyacrylamide gels is described. This method combines the well-known periodic acid/Schiff stain with protein blotting. Compared with direct staining of a polyacrylamide gel, the sensitivity is considerably increased. Using a set of glycoproteins, we have found the sensitivity to be about 4 ng carbohydrate.

Animals↗

PubMed1991

Glycosylation of extracellular superoxide dismutase studied by high-performance liquid chromatography and mass spectrometry.

Extracellular superoxide dismutase, EC-SOD, the main superoxide dismutase in biological fluids, is known from its lectin binding to be a glycoprotein. We have characterized the glycosylation of recombinant EC-SOD. A tryptic digest of the protein contained only one glycosylated peptide. This peptide was specifically bound to lectins and stained by periodic acid-Schiff stain. Although appearing very large on size-exclusion chromatography, it was shown to be glycosylated at only one site, asparagine-89, by specific cleavage with glycanases followed by mass spectrometry of the resulting peptide. Based on the binding properties of the peptide to concanavalin A and lentil lectin and the elution profile of N-glycanase-treated glycopeptide on ion-exchange chromatography, the carbohydrate appears to be the complex biantennary type with a core fucose.

Amino Acids↗

PubMed1988

Influence of calmodulin on the human red cell membrane skeleton.

The calcium receptor calmodulin interacts with components of the human red cell membrane skeleton as well as with the membrane. Under physiological salt conditions, calmodulin has a calcium-dependent affinity for spectrin, one of the major components of the membrane skeleton. It is apparent from our results that calmodulin inhibits the ability of erythrocyte spectrin (when preincubated with filamentous actin) to create nucleation centers and thereby to seed actin polymerization. The gelation of filamentous actin induced by spectrin tetramers is also inhibited by calmodulin. The inhibition is calcium dependent and decreases with increasing pH, similar to the binding of calmodulin to spectrin. Direct binding studies using aqueous two-phase partition indicate that calmodulin interferes with the binding of actin to spectrin. Even in the presence of protein 4.1, which is believed to stabilize the ternary complex, calmodulin has an inhibitory effect. Since calmodulin also inhibits the corresponding activities of brain spectrin (fodrin), it appears likely that calmodulin may modulate the organization of cytoskeletons containing actin and spectrin or spectrin analogues.

Actins↗

PubMed1987

Brain spectrin fragments and crosslinks actin filaments.

The effect of brain spectrin (fodrin) on actin has been studied using viscometry and fluorimetry. Brain spectrin resembles erythrocyte spectrin tetramer in its action on actin. Both proteins crosslink actin filaments giving rise to a large increase in the viscosity but fluorimetry shows that neither affects actin polymerization significantly. In addition, brain spectrin as well as erythrocyte spectrin fragments preformed actin filaments. Actin filaments incubated in the presence of either of the two proteins incorporate actin monomers at a much higher rate showing that more filament ends are generated.

Actins↗

PubMed1985

Effect of spectrin dimer on actin polymerization.

Spectrin dimer is shown to influence the polymerization behaviour of actin. The polymerization of both Mg2+- and Ca2+-actin is regulated by an enhancement in the rate of nucleation and a fragmentation of preformed actin filaments. In addition, spectrin decreases the critical concentration of Ca2+-actin but not that of Mg2+-actin. This suggests that the two types of actin may differ in their interaction with spectrin dimer probably due to the different conformations. Band 4.1 elevates the effects of spectrin under non-equilibrium conditions but its contribution is less at steady state.

Actins↗

PubMed1984

The rate of polymerization of rabbit skeletal muscle actin is enhanced by polyethylene glycol.

The effect of polyethylene glycol on the kinetics of actin polymerization was determined by monitoring the enhancement in the fluorescence of pyrenyl-labelled actin. The polymerization of actin at 15 mM KCl was in addition followed by viscometry and light scattering. All three methods showed that the overall rate of polymerization of actin increased 3-4-fold when the concentration of polyethylene glycol was increased from 0 to 6% (ww-1). A further increase in polyethylene glycol concentration to 10% (ww-1) caused a relatively small contribution to the increase in the rate of polymerization. The enhancement of the overall rate of polymerization by polyethylene glycol was also reflected in a significant decrease in the lag time observed when the time course of polymerization was followed by viscometry and light scattering. The steady-state value of fluorescence enhancement and critical concentration of actin were also influenced by polyethylene glycol and the results showed that the extent of polymerization was increased by an increase in the concentration of polyethylene glycol in solution. The effect of polyethylene glycol on both rate and extent of polymerization persisted at physiological salt concentration (150 mM KCl, 2 mM MgCl2). Since the rate of elongation was affected only to a small extent by polyethylene glycol, we propose that its main effect is on nucleation.

Actins↗