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Jan Johansson

Publications and source records attributed to Jan Johansson.

44 records · Page 3Linked to original sources
PubMed2002

Charge attraction and beta propensity are necessary for amyloid fibril formation from tetrapeptides.

Amyloid fibrils in which specific proteins have polymerized into a cross-beta-sheet structure are found in about 20 diseases. In contrast to the close structural similarity of fibrils formed in different amyloid diseases, the structures of the corresponding native proteins differ widely. We show here that peptides as short as 4 residues with the sequences KFFE or KVVE can form amyloid fibrils that are practically identical to fibrils formed in association with disease, as judged by electron microscopy and Congo red staining. In contrast, KLLE or KAAE do not form fibrils. The fibril-forming KFFE and KVVE show partial beta-strand conformation in solution, whereas the non-fibril-forming KLLE and KAAE show random structure only, suggesting that inherent propensity for beta-strand conformation promotes fibril formation. The peptides KFFK or EFFE do not form fibrils on their own but do so in an equimolar mixture. Thus, intermolecular electrostatic interactions, either between charged dipolar peptides or between complementary charges of co-fibrillating peptides favor fibril formation.

Amino Acid Sequence↗
PubMed2002

Molecular effects of proinsulin C-peptide.

The proinsulin C-peptide has been held to be merely a by-product in insulin biosynthesis, but recent reports show that it elicits both molecular and physiological effects, suggesting that it is a hormonally active peptide. Specific binding of C-peptide to the plasma membranes of intact cells and to detergent-solubilised cells has been shown, indicating the existence of a cell surface receptor for C-peptide. C-peptide elicits a number of cellular responses, including Ca(2+) influx, activation of mitogen-activated protein (MAP) kinases, of Na(+),K(+)-ATPase, and of endothelial NO synthase. The pentapeptide EGSLQ, corresponding to the C-terminal five residues of human C-peptide, mimics several of the effects of the full-length peptide. The pentapeptide displaces cell membrane-bound C-peptide, elicits transient increase in intracellular Ca(2+) concentration and stimulates MAP kinase signalling pathways and Na(+),K(+)-ATPase. The Glu residue of the pentapeptide is essential for displacement of the full-length C-peptide, and free Glu can partly displace bound C-peptide, suggesting that charge interactions are important for receptor binding. Many C-peptide effects, such as phosphorylation of MAP-kinases ERK 1 and 2, stimulation of Na(+),K(+)-ATPase and increases in intracellular calcium concentrations are inhibited by pertussis toxin, supporting interaction of C-peptide with a G-protein-coupled receptor. However, all C-peptide effects cannot be explained in this manner, and it is possible that additional interactions are involved. Combined, the available observations show that C-peptide is biologically active and suggest a molecular model for its physiological effects.

Animals↗
PubMed2002

Structural basis for interactions between lung surfactant protein C and bacterial lipopolysaccharide.

In the respiratory tract, recognition of bacterial endotoxin (lipopolysacharide, LPS) is a critical step of the innate host defense system directed against invading pathogens. Secretions of the airways contain proteins that have direct antimicrobial activity (lysozyme, lactoferrin, defensins, and cathelicidins) as well as complement factors and surfactant proteins that contribute to host defense. The hydrophobic surfactant protein C (SP-C) recognizes LPS (Augusto, L., Le Blay, K., Auger, G., Blanot, D., and Chaby, R. (2001) Am. J. Physiol. 281, L776-L785). In the present study, using synthetic analogs of SP-C, we demonstrate that the palmitoyl residues of SP-C are not required for the interaction with LPS and that both the hydrophilic and hydrophobic regions of SP-C are required for specific binding of a radiolabeled rough-type LPS. In addition, using LPS submitted to different chemical treatments as well as synthetic analogs of the lipid A moiety of LPS, we established that the terminal phosphate group at the reducing end of the lipid A disaccharide in alpha configuration is of crucial importance for recognition by SP-C. The N-linked fatty acyl chain on the reducing glucosamine of lipid A also takes part in the interaction. Dipalmitoyl phosphatidylcholine is not specifically required for the LPS-binding activity of SP-C, although a lipid environment significantly increases the binding. These results provide a basis for experiments on the role of SP-C in presentation of LPS to alveolar cells and for the design of drugs for the management of endotoxin-induced lung injury.

Amino Acid Sequence↗
PubMed2002

Antibacterial peptides in stimulated human granulocytes: characterization of ubiquitinated histone H1A.

Antibacterial peptides were isolated from human peripheral granulocytes of a healthy donor who had been treated with granulocyte-colony stimulating factor (G-CSF) and cortisol. Peptides were solubilized in acidified chloroform/methanol, and partitioned in chloroform/methanol/water. Water- soluble polypeptides were separated by cation-exchange and reversed-phase chromatography. Several previously characterized antibacterial polypeptides were identified; defensins 1-3, defensin 4, lysozyme, eosinophil cationic protein, and calgranulin A. In addition, several histone fragments were isolated and exhibited activity against the Gram- positive bacterium Bacillus megaterium strain Bm11. These fragments included two C-terminal fragments of histone H1A, three C-terminal fragments of histone H1D, one fragment of histone H1B, and two fragments of histone H4. The molecular masses of both histone H1A fragments, as determined by electrospray (ES) MS, were 270 Da higher than those calculated from their amino acid sequences. The two histone H1A fragments corresponded to Lys152-Lys222 (7527 +/- 1 Da) and Lys167-Lys222 (6023 +/- 1 Da). Tandem MS (MS/MS) of the 7.5 kDa and 6.0 kDa fragments indicated that the post-translational modification is on Lys222, the epsilon-amino group of which was conjugated with the alpha-carboxyl group of the tripeptide Arg-Gly-Gly. This finding was substantiated by digestion of the 7.5-kDa polypeptide with trypsin and analysis of the resulting peptides by ES MS and MS/MS. The tripeptide Arg-Gly-Gly corresponded uniquely to the three C-terminal residues of ubiquitin, demonstrating the presence of ubiquitinated histone H1A.

Anti-Bacterial Agents↗
PubMed2002

Hydrogen/deuterium exchange and aggregation of a polyvaline and a polyleucine alpha-helix investigated by matrix-assisted laser desorption ionization mass spectrometry.

The membrane-associated pulmonary surfactant protein C (SP-C), containing a polyvaline alpha-helix, and a synthetic SP-C analogue with a polyleucine helix (SP-C(Leu)) were studied by hydrogen/deuterium exchange matrix-assisted laser desorption ionization (MALDI) mass spectrometry. SP-C, but not SP-C(Leu), formed abundant amyloid fibrils under experimental conditions. In CD(3)OD/D(2)O, 91:9 (v/v), containing 2 mM ammonium acetate, SP-C(Leu) and SP-C exchanged 40% of their exchangeable hydrogens within 1 min. This corresponds to exchange of labile side-chain hydrogen atoms, hydrogens on the N- and C-terminal heteroatoms, and amide hydrogen atoms in the unstructured N-terminal regions. After approximately 300 h, four exchangeable hydrogen atoms in SP-C(Leu) and 10 in SP-C remained unexchanged. During this time period the ion current corresponding to singly charged SP-C decreased to <10% of the initial value due to the formation of insoluble aggregates that are not detected by MALDI mass spectrometry. In contrast, the ion current for SP-C(Leu) was maintained over this time period, although the peptides were incubated together. In combination, hydrogen/deuterium exchange and aggregation data indicate that the polyleucine peptide refolds into a helix after opening, while the unfolded polyvaline peptide forms insoluble beta-sheet aggregates rather than refolding into a helix. The SP-C helix, but not the SP-C(Leu) helix, is thus in a metastable state, which may contribute to the recently observed tendency of SP-C and its precursor to misfold and aggregate in vivo.

Animals↗
PubMed2002

Metaplastic columnar mucosa in the cervical esophagus after esophagectomy.

OBJECTIVE: To evaluate the pathogenesis of metaplastic processes within the esophagus using a human model in which the exact duration of reflux was known. SUMMARY BACKGROUND DATA: The pathogenesis of Barrett's esophagus (BE) is incompletely understood. Patients undergoing esophagectomy and gastric tube reconstruction represent a good model for studying the pathophysiology of columnar cell metaplasia of the human esophagus because the cervical esophagus is rarely or never exposed to gastric contents before the surgical procedure. METHODS: Thirty-two patients underwent manometry, simultaneous 24-hour pH and bilirubin monitoring, and endoscopy with biopsy 3 to 10.4 years after esophagectomy. The presence of columnar mucosa in the cervical esophagus was confirmed on histologic examination. The findings on endoscopy and histology were related to clinical data and the results of pH and bilirubin monitoring 1 cm proximal to the esophagogastrostomy. RESULTS: Fifteen (46.9%) of the 32 patients had metaplastic columnar mucosa within their cervical esophagus. Metaplasia was significantly more common in patients with a preoperative diagnosis of BE. The length of metaplastic mucosa correlated significantly with the degree of esophageal acid exposure, but the presence of abnormal bilirubin exposure was unrelated to the presence of metaplasia. The prevalence of metaplasia did not change with increasing time. Intestinal metaplasia was found within the columnar-lined segment in three patients 8.5, 9.5, and 10.4 years after esophagectomy. All patients with intestinal metaplasia had abnormal exposure of both acid and bilirubin, but the presence of combined reflux was not significantly higher in these patients compared with patients with nonintestinalized segments of columnar mucosa. CONCLUSIONS: Esophageal columnar metaplasia is a common complication after gastric pull-up esophagectomy. Metaplasia is more likely to develop in patients with previous BE than other patients. Metaplasia develops in response to squamous epithelial injury in predisposed individuals.

Adenocarcinoma↗
PubMedDate not supplied

Molecular and cellular effects of C-peptide--new perspectives on an old peptide.

New results present C-peptide as a biologically active peptide hormone in its own right. Although C-peptide is formed from proinsulin and cosecreted with insulin, it is a separate entity with biochemical and physiological characteristics that differ from those of insulin. There is direct evidence of stereospecific binding of C-peptide to a cell surface receptor, which is different from those for insulin and other related hormones. The C-peptide binding site is most likely a G-protein-coupled receptor. The association constant for C-peptide binding is approximately 3 x 10(9) M(-1). Saturation of the binding occurs already at a concentration of about 1 nM, which explains why C-peptide effects are not observed in healthy subjects. Binding of C-peptide results in activation of Ca2+ and MAPK-dependent pathways and stimulation of Na+,K(+)-ATPase and eNOS activities. The latter 2 enzymes are both deficient in several tissues in type 1 diabetes. There is some evidence that C-peptide, and insulin may interact synergistically on the insulin signaling pathway. Clinical evidence suggests that replacement of C-peptide, together with regular insulin therapy, may be beneficial in patients with type 1 diabetes and serve to retard or prevent the development of long-term complications.

Amino Acid Sequence↗