Biomedical subjects

Erik Portelius

Publications and source records attributed to Erik Portelius.

5 recordsLinked to original sources

PubMed2006

An Alzheimer's disease-specific beta-amyloid fragment signature in cerebrospinal fluid.

Pathogenic events in Alzheimer's disease (AD) involve an imbalance between the production and clearance of the neurotoxic beta-amyloid peptide (Abeta), especially the 42 amino acid peptide Abeta1-42. While much is known about the production of Abeta1-42, many questions remain about how the peptide is degraded. To investigate the degradation pattern, we developed a method based on immunoprecipitation combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry that determines the Abeta degradation fragment pattern in cerebrospinal fluid (CSF). We found in total 18 C-terminally and 2 N-terminally truncated Abeta peptides and preliminary data indicated that there were differences in the detected Abeta relative abundance pattern between AD and healthy controls. Here, we provide direct evidence that an Abeta fragment signature consisting of Abeta1-16, Abeta1-33, Abeta1-39, and Abeta1-42 in CSF distinguishes sporadic AD patients from non-demented controls with an overall accuracy of 86%.

Aged↗

PubMed2006

Determination of beta-amyloid peptide signatures in cerebrospinal fluid using immunoprecipitation-mass spectrometry.

Early pathogenic events in Alzheimer's disease (AD) involve increased production and/or reduced clearance of beta-amyloid (Abeta), especially the 42 amino acid fragment Abeta1-42. The Abeta1-42 peptide is generated through cleavage of the amyloid precursor protein by beta- and gamma-secretase and is catabolised by a variety of proteolytic enzymes such as insulin-degrading enzyme and neprilysin. Here, we describe a method that employs immunoprecipitation combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to determine the pattern of C-terminally truncated Abeta peptides in cerebrospinal fluid (CSF). Using antibodies coupled to magnetic beads, we have detected 18 C-terminally and 2 N-terminally truncated Abeta peptides in CSF. By determining the identity and profile of the truncated Abeta peptides, more insight may be gained about differences in the metabolism and structural properties of Abeta in AD. Finally, the Abeta fragment signatures may prove useful as a diagnostic test for AD.

Amino Acid Sequence↗

PubMed2005

Profiling an electrospray plume using surface-enhanced Raman spectroscopy.

We report the use of silver nanoparticles to obtain surface-enhanced Raman spectra of Crystal Violet in an electrospray plume. Surface enhancement allowed detection at low concentrations with the high specificity afforded by vibrational spectroscopy. SERS spectra were used to obtain an axial concentration profile closely matching that obtained in previous fluorescence experiments. SERS can provide more analyte structural information than has been obtainable from fluorescence studies of the plume.

Electrochemistry↗

PubMed2004

Mapping abeta amyloid fibril secondary structure using scanning proline mutagenesis.

Although the amyloid fibrils formed from the Alzheimer's disease amyloid peptide Abeta are rich in cross-beta sheet, the peptide likely also exhibits turn and unstructured regions when it becomes incorporated into amyloid. We generated a series of single-proline replacement mutants of Abeta(1-40) and determined the thermodynamic stabilities of amyloid fibrils formed from these mutants to characterize the susceptibility of different residue positions of the Abeta sequence to proline substitution. The results suggest that the Abeta peptide, when engaged in the amyloid fibril, folds into a conformation containing three highly structured segments, consisting of contiguous sequence elements 15-21, 24-28, and 31-36, that are sensitive to proline replacement and likely to include the beta-sheet portions of the fibrils. Residues relatively insensitive to proline replacement fall into two groups: (a) residues 1-14 and 37-40 are likely to exist in relatively unstructured, flexible elements extruded from the beta-sheet-rich amyloid core; (b) residues 22, 23, 29 and 30 are likely to occupy turn positions between these three structured elements. Although destabilized, fibrils formed from Abeta(1-40) proline mutants are very similar in structure to wild-type fibrils, as indicated by hydrogen-deuterium exchange and other analysis. Interestingly, however, some proline mutations destabilize fibrils while at the same time increasing the number of amide protons protected from hydrogen exchange. This suggests that the stability of amyloid fibrils, rather than being driven exclusively by the formation of H-bonded beta-sheet, is achieved, as in globular proteins, through a balance of stabilizing and destabilizing forces. The proline scanning data are most compatible with a model for amyloid protofilament structure loosely resembling the parallel beta-helix folding motif, such that each Abeta(15-36) core region occupies a single layer of a prismatic, H-bonded stack of peptides.

Amino Acid Substitution↗

PubMed2002

Cloning, characterisation, and expression of a novel gene encoding chlorite dismutase from Ideonella dechloratans.

The gene for chlorite dismutase was isolated from a lambda ZAP genomic library of Ideonella dechloratans using peptide sequences obtained from the purified protein. A nucleotide sequence of 1200 bp was determined. The chlorite dismutase gene codes for a 285-residue polypeptide, with the experimentally determined N-terminus of the mature protein at residue 38. The N-terminal part of the encoded peptide has the characteristics of a signal sequence for periplasmic proteins. The nucleotide sequence and deduced protein showed no homology to sequences found in the databases. The transcriptional start point of the chlorite dismutase gene was determined with a new primer extension technique using capillary electrophoresis. Expression of recombinant chlorite dismutase in E. coli resulted in an active enzyme with similar spectral properties as the native enzyme.

Amino Acid Sequence↗