Biomedical subjects

B Piekarska

Publications and source records attributed to B Piekarska.

21 records · Page 2Linked to original sources

PubMed1988

The effect of azo dyes on heat aggregation of IgG.

The mechanism of IgG heat aggregation was studied using IgG aggregates complexed with azo dyes to increase their solubility and stability. Heat dependent and heat independent steps of aggregation were differentiated. On heating IgG at the dye concentration exceeding 100 times that of protein, mainly dimers are formed, as judged from ultracentrifugation and chromatographic analysis, whereas high molecular weight derivatives appear at room temperature when the protein/dye ratio is decreased. The analysis of spectral changes following either the attachment or removal of the dye from IgG aggregates implies that only a part of the dye molecules is bound firmly and directly to the protein binding sites. These dye molecules which are easily removed by adsorption to cellulose or reduced by dithionate but migrate together with IgG aggregates on chromatography and electrophoresis, are supposed to constitute that part of the micelle which extrudes from the binding site and, hence, is fixed indirectly to protein. Various proteins with predominant beta-structure were also found to bind azo dyes when heated.

Azo Compounds↗

PubMed1988

The formation of soluble heat IgG aggregates for immunological studies.

The structural alteration associated with the aggregation of heated immunoglobulin molecules and the triggering of their effector reactivity was studied using soluble aggregate derivatives. Large but still soluble aggregate species were obtained by the formation of complexes of heated immunoglobulin molecules with azo dyes - Congo Red or Trypan Blue. Exposed peptide fragments in the area rearranged on heating were identified by short-lasting proteolysis. The altered area was in this way localized in the Fab portion of the heavy chain. The heavy chain fragment bordered by disulphides which stabilize the domains V and CH1 was indicated as a most probable peptide portion forming the link between the aggregating molecules. The obtained dye-aggregate species retain their effector activity. The effect of structural alterations in the Fab fragment on the Fc remains unclear.

Binding Sites↗

PubMedDate not supplied

Why Congo red binding is specific for amyloid proteins - model studies and a computer analysis approach.

BACKGROUND: The complexing of Congo red in two different ligand forms - unimolecular and supramolecular (seven molecules in a micelle) - with eight deca-peptides organized in a b-sheet was tested by computational analysis to identify its dye-binding preferences. Polyphenylananine and polylysine peptides were selected to represent the specific side chain interactions expected to ensure particularly the stabilization of the dye-protein complex. Polyalanine was used to verify the participation of non-specific backbone-derived interactions. MATERIAL AND METHODS: The initial complexes for calculation were constructed by intercalating the dye between the peptides in the middle of the beta-sheet. The long axis of the dye molecule (in the case of unimolecular systems) or the long axis of the ribbon-like micelle (in the case of the supramolecular dye form) was oriented parallel to the peptide backbone. This positioning maximally reduced the exposure of the hydrophobic diphenyl (central dye fragment) to water. In general the complexes of supramolecular Congo red ligands appeared more stable than those formed by individual dye molecules. Specific interactions (electrostatic and/or ring stacking) dominated as binding forces in the case of the single molecule, while non-specific surface adsorption seemed decisive in complexing with the supramolecular ligand. RESULTS: Both the unimolecular and supramolecular versions of the dye ligand were found to be likely to form complexes of sufficient stability with peptides. The low stability of the protein and the gap accessible to penetration in the peptide sheet seem sufficient for supramolecular ligand binding, but the presence of positively charged or hydrophobic amino acids may strengthen binding significantly. CONCLUSIONS: The need for specific interaction makes single-molecule Congo red binding rather unusual as a general amyloid protein ligand. The structural feature of Congo red, which enables specific and common interaction with amyloid proteins, probably derives from the ribbon-like self-assembled form of the dye.

Amyloid beta-Peptides↗