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A Engström

Publications and source records attributed to A Engström.

At least 37 records · Page 2Linked to original sources
PubMed1995

Macrophages, but not dendritic cells, present collagen to T cells.

Dendritic cells, such as epidermal Langerhans cells, play a crucial role for the antigen-specific priming of T cells. We have addressed the question whether dendritic cells present collagen, a major protein component in tissues through which dendritic cells migrate, i.e. the basement membrane, dermis, and synovial tissue. Langerhans cells, spleen cells and peritoneal macrophages were compared for antigen-presenting capacity using a panel of mouse T cell hybridomas reactive with different determinants on type II collagen, myelin basic protein, ovalbumin and pepsin. Langerhans cells did not present any of the type II collagen determinants, unless the antigen was administered as a 15-mer peptide, but did present myelin basic protein, ovalbumin and pepsin. Spleen cells and peritoneal macrophages, in contrast, presented all type II collagen determinants. This biased antigen presentation was also observed when Langerhans cells were pulsed with antigen in vivo. The inability to present type II collagen is related to the collagen sequence as such, since both native type II collagen, type II collagen alpha chains, as well as a type II collagen determinant incorporated in type I collagen, were not presented by Langerhans cells. In addition, granulocyte/macrophage colony-stimulating factor-expanded blood dendritic cells displayed the same biased antigen presentation, suggesting that the inability to present collagen is not restricted to dendritic cells localized in epidermis. B cell-deficient mice could prime a type II collagen-reactive T cell response, thus excluding B cells as obligatory antigen-presenting cells for the priming of collagen-reactive T cells. We suggest that neither Langerhans cells nor B cells, but macrophages are the primary antigen-presenting cells in the immune response towards type II collagen.

Amino Acid Sequence↗
PubMed1995

Characterization of a potassium channel toxin from the Caribbean Sea anemone Stichodactyla helianthus.

A peptide toxin, ShK, that blocks voltage-dependent potassium channels was isolated from the whole body extract of the Caribbean sea anemone Stichodactyla helianthus. It competes with dendrotoxin I and alpha-dendrotoxin for binding to synaptosomal membranes of rat brain, facilities acetylcholine release at an avian neuromuscular junction and suppresses K+ currents in rat dorsal root ganglion neurones in culture. Its amino acid sequence is R1SCIDTIPKS10RCTAFQCKHS20MKYRLSFCRK30TCGTC35. There is no homology with other K+ channel-blocking peptides, except for BgK from the sea anemone Bunodosoma granulifera. ShK and BgK appear to be in a different structural class from other toxins affecting K+ channels.

Amino Acid Sequence↗
PubMed1995

Identification of murine loci associated with susceptibility to chronic experimental autoimmune encephalomyelitis.

B10.RIII mice develop chronic and relapsing experimental autoimmune encephalomyelitis (EAE) after immunization with the myelin basic protein (MBP) peptide 89-101. The disease is associated with the major histocompatibility complex (MHC) (eae1). We have now investigated the importance of non-MHC regions for the EAE susceptibility in a cross between RIIIS/J and B10.RIII mice which share the MHC region but differ in disease susceptibility. Linkage analysis using microsatellite markers spanning the genome identified a region (eae2) on chromosome 15 which showed linkage to disease (P = 0.0002). Our data also suggest linkage to a second region (eae3) on chromosome 3 (P = 0.0024), and provide evidence for locus interactions between eae2 and eae3. These results provide clues to the genetic basis of multiple sclerosis.

Amino Acid Sequence↗
PubMed1994

T cell recognition of carbohydrates on type II collagen.

A critical event in an immune response is the T cell recognition of peptides bound to major histocompatibility complex (MHC) molecules on the surface of an antigen presenting cell (APC). Although the majority of eukaryotic proteins are glycosylated, it has not yet been shown that T cell recognition of such proteins involves recognition of the bound carbohydrates. Type II collagen (CII), the major protein constituent of joint cartilage, is posttranslationally modified by hydroxylation and glycosylation of lysines. In this report we show that posttranslational modifications of the immunodominant peptide CII(256-270) generate a structural determinant that is distinct from the determinant represented by the corresponding synthetic peptide. Elimination of carbohydrates, present on CII, by two different biochemical methods revealed that the carbohydrates, O-linked to the hydroxylysines within the CII(256-270) determinant, were crucial for the reactivity towards the posttranslationally modified peptide. Furthermore, a T cell hybridoma specific for the glycosylated determinant was stimulated by tryptic CII-peptides presented by fixed APCs, thus showing that the carbohydrates are involved in the trimolecular complex T cell receptor/peptide/MHC. Finally, the importance of the bound carbohydrates for the arthritogenicity of CII was investigated by comparing the development of arthritis after immunization with carbohydrate-depleted and glycosylated CII, respectively. Incidence, time of onset, and severity of the disease were significantly affected by the elimination of carbohydrates, whereas no significant difference in anti-CII antibody titers was seen.

Amino Acid Sequence↗
PubMed1994

Detoxication of base propenals and other alpha, beta-unsaturated aldehyde products of radical reactions and lipid peroxidation by human glutathione transferases.

Radiation and chemical reactions that give rise to free radicals cause the formation of highly cytotoxic base propenals, degradation products of DNA. Human glutathione transferases (GSTs; RX:glutathione R-transferase, EC 2.5.1.18) of classes Alpha, Mu, and Pi were shown to promote the conjugation of glutathione with base propenals and related alkenes. GST P1-1 was particularly active in catalyzing the reactions with the propenal derivatives, and adenine propenal was the substrate giving the highest activity. The catalytic efficiency of GST P1-1 with adenine propenal (kcat/Km = 7.7 x 10(5) M-1.s-1) is the highest so far reported with any substrate for this enzyme. In general, GST A1-1 and GST M1-1, in contrast to GST P1-1, were more active with 4-hydroxyalkenals (products of lipid peroxidation) than with base propenals. The adduct resulting from the Michael addition of glutathione to the alkene function of one of the base propenals (adenine propenal) was identified by mass spectrometry. At the cellular level, GST P1-1 was shown to provide protection against alpha, beta-unsaturated aldehydes. GST P1-1 added to the culture medium of HeLa cells augmented the protective effect of glutathione against the toxicity of adenine propenal and thymine propenal. No protective effect of the enzyme was observed in the presence of the competitive inhibitor S-hexylglutathione. GST P1-1 introduced into Hep G2 cells by electroporation was similarly found to increase their resistance to acrolein. The results show that glutathione transferases may play an important role in cellular detoxication of electrophilic alpha, beta-unsaturated carbonyl compounds produced by radical reactions, lipid peroxidation, ionizing radiation, and drug metabolism.

Acrolein↗
PubMed1994

Study of structure-activity relationship of fasciculin by acetylation of amino groups.

Dendroaspis angusticeps (green mamba) has two toxins, fasciculins, that are non-competitive inhibitors of acetylcholinesterase. Amino groups of fasciculin 2 were acetylated with acetic anhydride. The monoacetyl derivatives of the epsilon-amino groups (Lys 25, 32, 51 and 58) retained between 28 and 43% of the initial activity and that of the alpha-amino group 72%. Acetylation of Lys 25 that has the most reactive amino group decreased the activity by 65% apparently without producing structural perturbations, since the circular dichroism spectrum was not affected. The three-dimensional structure shows a cationic cluster formed by Lys 32, 51, Arg 24 and 28. A comparison of 175 sequences of homologous toxins shows that Lys 32 is unique for fasciculin. Acetylation of lysine residues in the cluster had a large effect and reduced the activity by 72% (Lys 32) and 57% (Lys 51). This suggests an important role for the cationic cluster. Lys 25 together with Lys 32 and 51 were, therefore, assumed to be in the active site.

Acetylation↗
PubMed1994

Purification and characterization of integrin alpha 9 beta 1.

A new beta 1-containing integrin was isolated from rat liver by affinity chromatography on Sepharose conjugated with the peptide GRGDSPC. The interaction was weakened but not abolished when the arginine and/or aspartic acid in the peptide were replaced with lysine and glutamic acid, respectively. In contrast, the cysteine was necessary for binding of the integrin. The beta 1-associated protein, referred to as alpha 9, had an N-terminal amino acid sequence related to but distinct from previously described integrin alpha-subunits. In addition, an internal peptide sequence was obtained which confirmed that the protein is a new member of the family of integrin alpha-subunits. An antiserum raised against a synthetic peptide corresponding to amino acids 1-16 of alpha 9 reacted specifically with this protein and was used to identify alpha 9 in several tissues. The integrin alpha 9 beta 1 was not retained on Sepharose conjugated with Englebreth-Holm-Swarm tumor (EHS)-laminin, collagen type I, or a 105-kDa cell-binding fragment of fibronectin. However, it did bind specifically to EHS-laminin and collagen type I adsorbed to plastic microtiter wells. The sites of the interactions were localized to fragment E8 of EHS-laminin and to cyanogen bromide fragment 8 of collagen alpha 1(I) and were not inhibited by soluble RGD-containing peptides. The results indicate that alpha 9 beta 1 is a widely distributed laminin/collagen receptor which may have additional, yet unidentified ligands.

Amino Acid Sequence↗
PubMed1994

Purification and characterization of a human neutrophil lipocalin (HNL) from the secondary granules of human neutrophils.

A 45 kDa-protein was purified from the granules of human neutrophils. The protein consists of two apparently identical subunits. The isoelectric point was pH 8.40, and the molecular weight 45 kDa (unreduced) or 24 kDa (reduced). Treatment of the protein with Endoglucosidase F resulted in a reduction in the molecular weight to 20 kDa, indicating the presence of N-linked carbohydrate. The extinction coeffient was E1%,1cm = 13.76 at 280 nm. The 60 amino acid sequence revealed up to 65% sequence homology with rat alpha 2-microglobulin-related protein, which belongs to the lipocalin family. The protein co-sedimented with secondary (specific) granule marker proteins and correlated to the neutrophil content of Lactoferrin (r = 0.81, p < 0.001) and was estimated to be 0.59 microgram 10(-6) cells. Release studies showed that the neutrophils released 51.4 +/- 9.0% of the total cellular content of the protein when they were exposed to serum-opsonized particles, which was much higher than the release of Myeloperoxidase (12.7 +/- 3.5%) and Lactoferrin (22.9 +/- 4.7%). The N-terminal and four tryptic fragment amino acid sequence of the protein was identical with an N-formyl peptide binding 24 kDa protein and gelatinase associated protein of human neutrophils. In conclusion, we have purified and characterized a protein, human neutrophil lipocalin (HNL), from the secondary granules of human neutrophils and shown that it is readily mobilized from the neutrophils upon stimulation.

Acute-Phase Proteins↗
PubMed1993

An elongated form of T4 glutaredoxin with four extra residues.

Two different forms of T4 glutaredoxin (thioredoxin) arising from the same gene on a multicopy plasmid in an Escherichia coli expression system have been isolated and characterized. Up to one-fourth of purified T4 glutaredoxin has an extension of four amino acids in the carboxy terminus, with the sequence aspartate, arginine, isoleucine, lysine. This four-residue extension may be caused by a translational +1 frameshift at the UGA terminator codon.

Amino Acid Sequence↗
PubMed1993

A potassium channel toxin from the secretion of the sea anemone Bunodosoma granulifera. Isolation, amino acid sequence and biological activity.

A peptide toxin affecting potassium channels was isolated from the sea anemone Bunodosoma granulifera. It facilitates acetylcholine release at avian neuromuscular junctions, competes with dendrotoxin I, a probe for voltage-dependent potassium channels, for binding to synaptosomal membranes of rat brain with a Ki of 0.7 nM and suppresses K+ currents in rat dorsal root ganglion neurones in culture. It represents a new structural type of potassium channel toxin with the sequence V1RCDWFKETA10CRHAKSLGNC20RTSQKYRANC30AKTLQCC37 (M(r) 4275, three disulfides).

Amino Acid Sequence↗
PubMed1993

Identification of two juxtamembrane autophosphorylation sites in the PDGF beta-receptor; involvement in the interaction with Src family tyrosine kinases.

Two novel sites of autophosphorylation were localized to the juxtamembrane segment of the human platelet-derived growth factor (PDGF) beta-receptor. To evaluate the importance of these phosphorylation sites, receptor mutants were made in which Tyr579, Tyr581 or both were replaced with phenylalanine residues; the receptor mutants were stably expressed in porcine aortic endothelial cells. Compared with the wild-type receptor, the Y579F and Y581F mutants were less able to mediate association with and activation of the Src family tyrosine kinases. The ability of these phosphorylation sites to mediate directly the binding of the Src family proteins was also demonstrated by using phosphotyrosine-containing synthetic peptides representing the juxtamembrane sequence of the receptor. Both the Y579F and Y581F mutants were similar to the wild-type receptor with regard to their protein tyrosine kinase activity and ability to induce mitogenicity in response to PDGF-BB. A conclusive evaluation of the role of the Src family members in signal transduction could, however, not be made since our attempt to prevent completely the association by mutation of both Tyr579 and Tyr581, resulted in loss of kinase activity and was therefore not informative. The present data, together with previous observations, demonstrate a high degree of specificity in the interaction between different autophosphorylation sites in the PDGF beta-receptor and downstream components in the signal transduction pathway.

Amino Acid Sequence↗
PubMed1993

Identification of two expressed flagellin genes in the insect pathogen Bacillus thuringiensis subsp. alesti.

Flagellin from Bacillus thuringiensis subspecies alesti strain Bt75 was isolated both from the culture medium and from flagella. Two protein forms with molecular masses close to 32 kDa were obtained from flagella; one form was identical to the flagellin purified from the culture medium. The N-terminal amino acid sequences were identical for both forms. Two genes coding for flagellin have been identified in B. thuringiensis subsp. alesti. The flaB gene was cloned and sequenced in its entire length. The clone containing the flaA gene was incomplete. Both genes were expressed in the mid-exponential growth phase. The flaB gene was flanked by long (355 bp) direct repeats protruding into the coding region in both the N- and C-terminal parts of the gene. DNA sequences related to the flaB gene were found in most other B. thuringiensis subspecies, and in two of them, subsp. kurstaki and subsp. entomocidus, such sequences were present in multiple copies.

Amino Acid Sequence↗
PubMed1993

Cannabis and schizophrenia: a longitudinal study of cases treated in Stockholm County.

By means of the Stockholm County inpatient care register we identified all cases treated with a diagnosis of cannabis dependence and psychosis, not necessarily at the same occasion, during 1971-1983. By scrutinizing medical records, we evaluated the diagnosis according to DSM-III-R and we assessed the history of substance abuse as well as the psychiatric history and clinical course. We identified 229 cases during the follow-up; 112 of these cases (49%) fulfilled the DSM-III-R criteria for schizophrenia. The majority of the schizophrenics had prominent positive symptoms and a sudden onset of disease, and 69% of the cases had a record of heavy cannabis abuse at least 1 year before onset of psychotic symptoms. The high number of verified DSM-III-R cases of schizophrenia in this cohort and the temporal relation between cannabis abuse and schizophrenia further support the hypothesis that cannabis abuse may be a risk factor for schizophrenia. We confirmed previous observations that cannabis-associated schizophrenia often has a sudden onset and prominent positive symptoms.

Cannabis↗
PubMed1992

Identification of a peptide antagonist for platelet-derived growth factor.

A series of peptides derived from the primary sequence of the B-chain of platelet-derived growth factor (PDGF) was analyzed for their ability to inhibit the binding of 125I-PDGF-AA and 125I-PDGF-BB to PDGF alpha-receptors and PDGF beta-receptors, respectively. A 13-amino acid peptide (ANFLVWEIVRKKP), corresponding to amino acids 116-121 and 157-163 in PDGF B-chain, was found to compete with binding to both alpha- and beta-receptors. Modification of this peptide on the tryptophan residue increased its receptor competing activity. The peptide was found to be a receptor antagonist, since it inhibited dimerization and autophosphorylation of PDGF receptors. When analyzed on intact cells, the peptide was found to have, in addition to the specific inhibitory effect at the receptor level, a nonspecific inhibitory effect on [3H]thymidine incorporation. Our study has identified two regions in PDGF that are of importance for receptor interaction.

Amino Acid Sequence↗
PubMed1992

Cloning and heterologous expression of cDNA encoding class alpha rat glutathione transferase 8-8, an enzyme with high catalytic activity towards genotoxic alpha,beta-unsaturated carbonyl compounds.

A cDNA clone, lambda GTRA8, encoding rat glutathione transferase subunit 8 has been isolated from a lambda gt10 rat hepatoma cDNA library. The previously known amino acid sequence of the enzyme was used to design primers for a polymerase chain reaction that yielded a 0.3 kb DNA fragment from the hepatoma library. The 0.3 kb fragment was used as a probe for screening and a 0.9 kb cDNA clone containing a complete open reading frame was obtained. After DNA sequencing and subcloning into an expression vector, the enzyme was expressed in Escherichia coli and purified. Specific activities and kcat./Km values were determined for a number of substrates, including alpha,beta-unsaturated carbonyl compounds. The highest activity was obtained with 4-hydroxyalkenals and with acrolein, genotoxic products of lipid peroxidation. In addition, the rat class Alpha glutathione transferase 8-8 displays high catalytic activity in the reaction between glutathione and the diuretic drug ethacrynic acid, a compound normally considered as a substrate characteristic for class Pi glutathione transferases.

Amino Acid Sequence↗
PubMed1992

Identification of an immunodominant type-II collagen peptide recognized by T cells in H-2q mice: self tolerance at the level of determinant selection.

The T cell recognition of type-II collagen (CII) in H-2q mice, susceptible to CII-induced arthritis, was analyzed. With the use of T cell hybridomas derived from rat CII-immunized mice, a peptide corresponding to amino acids 245-270 on chick CII was found to harbor a T cell epitope which is present on heterologous CII (chick, rat, human, and bovine CII) but not on autologous CII. It was shown that this epitope was located within amino acids 260-270, although flanking regions in either direction were necessary for proper recognition. A peptide corresponding to human CII (256-270) was used for further studies. A single amino acid difference at position 266 between mouse CII (aspartic acid) and heterologous CII (glutamic acid) strongly influenced recognition of this peptide. No response towards the mouse peptide was seen with any of the T cell hybridomas. Inhibition studies revealed that the mouse peptide did not bind as well to major histocompatibility complex as the corresponding heterologous peptide. Both peptides gave rise to a T cell response after immunization. However, immunization with the heterologous peptide resulted in a response strictly directed to rat CII and the immunogen while immunization with the autologous peptide elicited T cells which reacted in a heteroclitic fashion, with a stronger response to the heterologous peptide than to the autologous peptide, and did respond to rat CII but not to mouse CII. We suggest that aspartic acid in position 266 results in a cryptic determinant in mouse CII which is neither recognized after CII immunization nor capable of tolerance induction. A glutamic acid at position 266, however, gives rise to an immunodominant epitope which is recognized by a large proportion of the T cells activated after immunization with heterologous CII.

Amino Acid Sequence↗
PubMed1992

Human islet amyloid polypeptide at pharmacological levels inhibits insulin and phorbol ester-stimulated glucose transport in in vitro incubated human muscle strips.

Human islet amyloid polypeptide, at concentrations of 1-100 nmol/l, has been demonstrated to inhibit the insulin-stimulated increase in rat muscle glycogen content. However, at physiological concentrations (1-10 pmol/l) of islet amyloid polypeptide, no effects have been reported. We tested the effect of a wide range of concentrations of human islet amyloid polypeptide on insulin- and phorbol ester-stimulated 3-0-methylglucose transport in in vitro incubated human skeletal muscle. Muscle specimens from the quadriceps femoris muscle were obtained from 23 healthy subjects with the use of a newly-developed open muscle biopsy technique. Human islet amyloid polypeptide at a concentration of 100 nmol/l had no effect on basal glucose transport, but inhibited the stimulatory effect of a maximal insulin concentration (1000 microU/ml) by 69% (p less than 0.001). The presence of human islet amyloid polypeptide at 1, 10 and 100 nmol/l decreased the effect of 100 microU/ml of insulin on glucose transport by 61% (p less than 0.05), 78% (p less than 0.05) and 76% (p less than 0.05), respectively. Similarly, human islet amyloid polypeptide at a concentration of 10 nmol/l inhibited phorbol ester-stimulated glucose transport by 100% (p less than 0.05). The inhibitory effects of human islet amyloid polypeptide on glucose transport were present in the muscle strips despite no net changes in glycogen content. Human islet amyloid polypeptide at 10 and 100 pmol/l had no effect on the rate of insulin-stimulated glucose transport.(ABSTRACT TRUNCATED AT 250 WORDS)

3-O-Methylglucose↗