Property of a new Prussian blue-bounded iron complex able to peroxidate non-saturated fatty acids with a tendency to create conditions that may encourage ferroptosis.

Ferroptosis is a cell death process caused by redox imbalance in the cell environment. However, the cell death pathway proves beneficial in anticancer therapy, so compounds inducing ferroptosis are sought. The paper presents a newly synthesized iron complex named FeT, composed of ferricyanide and tartrate, which seems to meet these expectations. It is relatively stable, easily soluble in water and capable of peroxidating unsaturated fatty acids. T24 bladder cells were used as model cells. Preliminary studies demonstrated a strong inhibitory effect of this compound on cell proliferation. The cytotoxicity of FeT was assessed. Independently, it initiates caspase activity, indicating the complex cellular impact of this compound. This effect is compellingly the result of FeT penetration into the cell's interior with possible direct damage to mitochondria, thus explaining the involvement of apoptosis in cell death. At the same time, after penetrating into the cell, it causes an increase in reactive oxygen species (ROS), lipid peroxidation and a decrease in reduced glutathione, which is interpreted as to cause ferroptosis. In turn, reducing mitochondrial potential may indicate both ferroptosis and an internal pathway to apoptosis.

Intramolecular immunological signal hypothesis revived--structural background of signalling revealed by using Congo Red as a specific tool.

Micellar structures formed by self-assembling Congo red molecules bind to proteins penetrating into function-related unstable packing areas. Here, we have used Congo red--a supramolecular protein ligand--to investigate how the intramolecular structural changes that take place in antibodies following antigen binding lead to complement activation. According to our findings, Congo red binding significantly enhances the formation of antigen-antibody complexes. As a result, even low-affinity transiently binding antibodies can participate in immune complexes in the presence of Congo red, although immune complexes formed by these antibodies fail to trigger the complement cascade. This indicates that binding of antibodies to the antigen may not, by itself, fulfill the necessary conditions to generate the signal which triggers effector activity. These findings, together with the results of molecular dynamics simulation studies, enable us to conclude that, apart from the necessary assembling of antibodies, intramolecular structural changes generated by strains which associate high- affinity bivalent antibody fitting to antigen determinants are also required to cross the complement activation threshold.

Egg yolk platelet proteins from Xenopus laevis are amyloidogenic.

The association of amphibian (Xenopus laevis) egg yolk platelet proteins, represented predominantly by lipovitellin, was studied as a model of the formation of amyloid deposits. Two kinds of molecular organization formed by this protein material - native and heat-denatured - were found to exhibit amyloid properties although they differ significantly in structural organization. The first consisted in protein molecules arranged in the natural, physiological, net-like platelet organization, with a tendency to orient uni-directionally. The second was obtained by the gradual removal of Congo red from lipovitellin denatured by heating in an excess of dye. This procedure produced the twisted fibrillar organization of molecules typical for amyloids, represented predominantly by end-to-end associated major polypeptide chains of lipovitellin. Both native and denatured structural forms bind Congo red and produce a green birefringence effect, confirming the near parallel alignment of the complexed Congo red molecules. However, a dye(1,4-bis(1-amino-4-sulfonaphtyl-2-azo)phenylene) closely related to Congo red but with a very weak self-assembling tendency appeared inactive when the spectral shift was studied in a cross-polarization system, indicating in this way that dye supramolecularity is an extra factor which may determine binding to amyloid proteins and specific spectral effects.

Heat-induced formation of a specific binding site for self-assembled Congo Red in the V domain of immunoglobulin L chain lambda.

Moderate heating (40-50 degrees C) of immunoglobulins makes them accessible for binding with Congo Red and some related highly associated dyes. The binding is specific and involves supramolecular dye ligands presenting ribbon-like micellar bodies. The L chain lambda dimer, which upon heating disclosed the same binding requirement with respect to supramolecular dye ligands, was used in this work to identify the site of their attachment. Two clearly defined dye-protein (L lambda chain) complexes arise upon heating, here called complex I and complex II. The first is formed at low temperatures (up to 40-45 degrees C) and hence by a still native protein, while the formation of the second one is associated with domain melting above 55 degrees C. They contain 4 and 8 dye molecules bound per L chain monomer, respectively. Complex I also forms efficiently at high dye concentration even at ambient temperature. Complex I and its formation was the object of the present studies. Three structural events that could make the protein accessible to penetration by the large dye ligand were considered to occur in L chains upon heating: local polypeptide chain destabilization, VL-VL domain incoherence, and protein melting. Of these three possibilities, local low-energy structural alteration was found to correlate best with the formation of complex I. It was identified as decreased packing stability of the N-terminal polypeptide chain fragment, which as a result made the V domain accessible for dye penetration. The 19-amino acid N-terminal fragment becomes susceptible to proteolytic cleavage after being replaced by the dye at its packing locus. Its splitting from the dye-protein complex was proved by amino acid sequence analysis. The emptied packing locus, which becomes the site that holds the dye, is bordered by strands of amino acids numbered 74-80 and 105-110, as shown by model analysis. The character of the temperature-induced local polypeptide chain destabilization and its possible role in intramolecular antibody signaling is discussed.

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.

Evidence that supramolecular Congo red is the sole ligation form of this dye for L chain lambda derived amyloid proteins.

The mechanism of Congo red binding to amyloid protein was studied in order to establish which of two structural dye versions present in water solutions--unimolecular and supramolecular--represent its actual ligation form. Immunoglobulin L chain lambda of amyloidogenic nature, expressed by Congo red binding and easy gel formation, was used as the model amyloid protein. Congo red was coassembled with rhodamine B, designed to be a marker of the Congo red micellar organisation in complexation with protein. The particular suitability of rhodamine B for this role results from significant difference in its binding affinity to Congo red and to protein. It associates readily with Congo red, becoming incorporated into its micellar organisation, but as homogenous dye it shows an almost complete inability to bind to protein. In view of these properties, Congo red was used as a vehicle to draw rhodamine B into complexation with protein, at the same time supplying evidence of its supramolecular ligation form. The results show that both soluble amyloid precursor L chain and the derived gel material attach rhodamine B coassembled with Congo red but not the homogenous rhodamine B. Despite its dynamic, supramolecular character, Congo red participates in complexation with amyloid proteins as an integral ligand unit.

Supramolecularity creates nonstandard protein ligands.

Congo red and a group of structurally related dyes long used to stain amyloid proteins are known to associate in water solutions. The self-association of some dyes belonging to this group appears particularly strong. In water solutions their molecules are arranged in ribbon-like micellar forms with liquid crystalline properties. These compounds have recently been found to form complexes with some native proteins in a non-standard way. Gaps formed by the local distribution of beta-sheets in proteins probably represent the receptor sites for these dye ligands. They may result from higher structural instability in unfolding conditions, but also may appear as long range cooperative fluctuations generated by ligand binding. Immunoglobulins G were chosen as model binding proteins to check the mechanism of binding of these dyes. The sites of structural changes generated by antigen binding in antibodies, believed to act as a signal propagated to distant parts of the molecule, were assumed to be suitable sites for the complexation of liquid-crystalline dyes. This assumption was confirmed by proving that antibodies engaged in immune complexation really do bind these dyes; as expected, this binding affects their function by significantly enhancing antigen binding and simultaneously inhibiting C1q attachment. Binding of these supramolecular dyes by some other native proteins including serpins and their natural complexes was also shown. The strict dependence of the ligation properties on strong self-assembling and the particular arrangement of dye molecules indicate that supramolecularity is the feature that creates non-standard protein ligands, with potential uses in medicine and experimental science.