Jaroslava Bagelova

Effect of Fe 3 O 4 magnetic nanoparticles on lysozyme amyloid aggregation

Peptide amyloid aggregation is a hallmark of several human pathologies termed amyloid diseases. We have investigated the effect of electrostatically stabilized magnetic nanoparticles of Fe(3)O(4) on the amyloid aggregation of lysozyme, as a prototypical amyloidogenic protein. Thioflavin T fluorescence assay and atomic force microscopy were used for monitoring the inhibiting and disassembly activity of magnetic nanoparticles of Fe(3)O(4). We have found that magnetic Fe(3)O(4) nanoparticles are able to interact with lysozyme amyloids in vitro leading to a reduction of the amyloid aggregates, thus promoting depolymerization; the studied nanoparticles also inhibit lysozyme amyloid aggregation. The ability to inhibit lysozyme amyloid formation and promote lysozyme amyloid disassembly exhibit concentration-dependent characteristics with IC50 = 0.65 mg ml(-1) and DC50 = 0.16 mg ml(-1) indicating that nanoparticles interfere with lysozyme aggregation already at stoichiometric concentrations. These features make Fe(3)O(4) nanoparticles of potential interest as therapeutic agents against amyloid diseases and their non-risk exploitation in nanomedicine and nanodiagnostics.

Acridine derivatives inhibit lysozyme aggregation

We have screened a library of structurally distinct acridine derivatives (19 compounds) for their ability to inhibit lysozyme amyloid aggregation in vitro. Studied acridines were divided into three structurally different groups depending on the molecule planarity and type of the side chain—planar acridines, spiroacridines and tetrahydroacridines. Thioflavine T fluorescence assay and transmission electron microscopy were used for monitoring the inhibiting activity of acridines. We have found that both the structure of the acridine side chains and molecule planarity influence their antiamyloidogenic activity. The planar acridines inhibited lysozyme aggregation effectively. Spiroacridines and tetrahydroacridines had no significant effect on the prevention of lysozyme fibrillization, probably resulting from the presence of the heterocyclic 5-membered ring and non-planarity of molecule. Moreover, in the presence of some tetrahydroacridines the enhanced extent of aggregation was detected. We identified the most active acridine derivates from studied compound library characterized by low micromolar IC50 values, which indicate their possible application for therapeutic purpose.

Effect of varying polyglutamate chain length on the structure and stability of ferricytochrome c.

The effect of varying polyglutamate chain length on local and global stability of horse heart ferricytochrome c was studied using scanning calorimetry and spectroscopy methods. Spectral data indicate that polyglutamate chain lengths equal or greater than eight monomer units significantly change the apparent pK(a) for the alkaline transition of cytochrome c. The change in pK(a) is comparable to the value when cytochrome c is complexed with cytochrome bc(1). Glutamate and diglutamate do not significantly alter the temperature transition for cleavage of the Met(80)-heme iron bond of cytochrome c. At low ionic strength, polyglutamates consisting of eight or more glutamate monomers increase midpoint of the temperature transition from 57.3+/-0.2 to 66.9+/-0.2 degrees C. On the other hand, the denaturation temperature of cytochrome c decreases from 85.2+/-0.2 to 68.8+/-0.2 degrees C in the presence of polyglutamates with number of glutamate monomers n >or approximately equal 8. The rate constant for cyanide binding to the heme iron of cytochrome c of cytochrome c-polyglutamate complex also decreases by approximately 42.5% with n>or approximately equal 8. The binding constant for the binding of octaglutamate (m.w. approximately 1000) to cyt c was found to be 1.15 x 10(5) M(-1) at pH 8.0 and low ionic strength. The results indicate that the polyglutamate (n>or approximately equal 8) is able to increase the stability of the methionine sulfur-heme iron bond of cytochrome c in spite of structural differences that weaken the overall stability of the cyt c at neutral and slightly alkaline pH.

Heat‐induced conformational transition of cytochrome c observed by temperature gradient gel electrophoresis at acidic pH

Temperature‐gradient gel electrophoresis (TGGE) has been used to study the thermal unfolding of ferricytochrome c in low and high concentrations of acetic acid. It has been observed that the mobility of cytochrome c is a linear function of temperature when the system is characterized by a homogeneous population of conformation‐state, single molecular species. Within the transition temperature range, the mobility clearly displays the characteristic sigmoidal shape describing the transitions of protein unfolding. The data obtained by TGGE were used to estimate the apparent thermodynamic parameters (enthalpy change ΔHvh and transition temperature Tm), associated with the transition of unfolding. The accuracy of the apparent thermodynamic parameters obtained by this method agrees within error limits with the values obtained by direct calorimetric measurements using differential scanning calorimetry (DSC).

EFFECT OF POLYGLUTAMATE ON THE THERMAL STABILITY OF FERRICYTOCHROME C

The effect of saturated solutions of polyglutamate on the thermal stabilities of the Met‐80‐heme iron bond and of the ferricytochrome c as a whole were studied by absorption spectroscopy and differential scanning calorimetry at pH 7.0. According to spectral data the midtransition temperature of the cleavage of the sulfur‐iron bond was 57.4±0.5 °C and 66.8±0.5 °C for cytochrome c and cytochrome c‐polyglutamate complex, respectively. Addition of polyglutamate to cytochrome c at pH 7.0 alters the denaturation properties of the protein. As follows from DSC scans, the denaturation temperature for cytochrome c is decreased from 85.4±0.2 °C to 68.7±0.2 °C in the presence of the saturated amount of polyglutamate. The protein stability in terms of Gibbs energy change at protein unfolding amount to ΔG(25°C)=22.7±2.7 and 32.0±2.2 kJ/mol, for cytochrome c and cytochrome c‐polyglutamate complex, respectively, at pH 7.0. It is evident that polyglutamate increases the thermal stability of the sulfur‐iron bond and decreases the denaturation temperature of the cytochrome c molecule as a whole. The complex thermal stability in terms of Gibbs energy is not lower than that of cytochrome c in the range of physiological temperatures.

Polyanion induced circular dichroism of Thioflavin T.

Thioflavin T (ThT) is amyloid specific fluorescence dye possessing the properties of molecular rotor. We have shown that Thioflavin T forms complexes with non-peptide polyanions heparin, polyadenylate and polystyrene sulphonate by means of absorption spectroscopy. In the presence of chiral polyanions - heparin and polyadenylate - induced optical activity of ThT occurs whereas interaction with achiral polystyrene sulphonate (PSS) does not lead to production of induced circular dichroism signal. The positively charged ThT forms centre for ordered binding of chiral polyanion. Similarly, complexation of structurally different chromophore 9-aminoacridine with polyanions has led to induction of optical activity only in the presence of chiral ones. We suggest that, primarily, the optical activity of environment plays important role in inducing optical activity of achiral compounds.

The interfacial behavior of cytochrome c studied by pendant-drop technique.

The adsorption properties of cytochrome c (cyt c) were characterized by surface tension measurements using the pendant‐drop method employing the digital image analysis of the drop shape. The method was applied to the study of the protein conformation change due to acidification at low ionic strength. The observation of the saturated steady‐state surface tension shows that decrease in pH induces its cooperative change centered around pH 2.5. This value is equal to the value of apparent pK of the acid‐induced transition of the horse ferricyt c from a native state to the unfolded conformation. This indicates that the saturated steady‐state surface tension is sensitive to the conformation of cyt c in bulk phase, and the pendant‐drop method might be used to monitor changes in the tertiary structure of proteins.