Aggregation behavior of novel heptamethine cyanine dyes upon their binding to native and fibrillar lysozyme

Abstract

Two newly synthesized symmetrical heptamethine cyanine dyes, AK7-5 and AK7-6, absorbing in the region of low autofluorescence of biological samples, have been tested for their ability to detect proteins aggregated into amyloid fibrils. In aqueous solution these probes possess three absorption bands corresponding to the monomer, dimer and H-aggregate species. The association of the dye with fibrillar lysozyme was followed by the enhancement of the monomer band and the reduction of the H-band. The absorption spectra measured at various fibril concentrations were analyzed in terms of the model allowing for the shift of equilibria between various dye species due to the binding of monomers and dimers of AK7-5 and AK7-6 to amyloid fibrils. The association constants and stoichiometries of the dye-fibril complexation have been evaluated. In contrast to fibrillar lysozyme, the native protein brought about strong J-aggregate formation accompanied by a marked drop in the absorbance of the dye monomer species. Quantum chemical calculations and simple docking studies showed that AK7-5 and AK7-6 monomers can bind to the grooves, running parallel to the fibril axis. Due to their ability to distinguish between the native and fibrillar protein states, the novel cyanines are recommended as complementary to existing amyloid markers.

Removing the Obstacle of Dye‐Sensitized Upconversion Luminescence in Aqueous Phase to Achieve High‐Contrast Deep Imaging In Vivo

“…Compared with the absorption spectra in DMF (Figure S5, Supporting Information), a strong absorption band around 695 nm emerged in water (Figure 1b), which is the characteristic absorption of the H‐dimers. [ 12 ] In accordance with the photoluminescence of the dye, the UCL of UCNPs was sensitized by Car‐Cl with a maximum enhancement of ≈613‐fold in DMF, but no obvious UCL enhancement was observed in H 2 O (Figure 1c, Figure S4c,d, Supporting Information). Notably, the fluorescence intensity of Car‐Cl on the surface of NaYF 4 nanoparticles in DMF reached the maximum at a loading capacity of 11 nmol mg −1 , followed by a decrease of intensity with further increasing the loading amount of dye.…”

Novel Cyanine Dyes as Potential Amyloid Probes: A Fluorescence Study

“…By and large, the rise in the fluorescence intensity of monomer band can be caused by the two processes: i) the growth of the monomer concentration due to a shift of equilibrium between the different dyes forms in the buffer after addition of the protein, as was previously demonstrated using absorption spectroscopy [42]; ii) increase of the dye quantum yield arising from its immobilization on the protein binding site. The interference between these processes complicates the quantitative analysis of the obtained results.…”

“…At the first step of study we analysed the emission and excitation spectra of AK7-5 and AK7-6 in an organic solvent and an aqueous solution. Recently, using the absorption spectroscopy technique we have found that both the above dyes can form non-fluorescing H-aggregates in an aqueous solution, but tend to disaggregate in the presence of protein [42]. In an organic solvent, DMSO, AK7-5 and AK7-6 monomers display fluorescence emission maxima at 835 and 839 nm, respectively, while fluorescence excitation maxima are observed at 816 nm for both dyes (Fig.…”

“…The interference between these processes complicates the quantitative analysis of the obtained results. Taking into account the absorption spectroscopy data [42] it can be assumed that the emission band of 600-800 nm corresponds to the H-dimers and H-aggregates of the examined dyes. This finding is especially interesting because, as mentioned above, in an aqueous media H-dimers and Haggregates are commonly uncapable of fluorescing.…”

Novel Phosphonium Dye TDV1 as a Potential Fluorescent Probe to Monitor DNA Interactions with Lysozyme Amyloid Fibrils

“…Among a variety of fluorescent compounds currently used in the DNA and amyloid fibrils studies an important place belongs to the dyes of cyanine family [16][17][18][19][20]. To exemplify, the oxazole yellow homodimer, which has EEJP 2 2019 Olga Zhytniakivska, Uliana Tarabara et al…”