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Interaction and inhibitory influence of the azo dye carmoisine on lysozyme amyloid fibrillogenesis

Abstract

The binding of the common food colorant carmoisine and its inhibitory effect on amyloid fibrillation in lysozyme have been investigated. Since humans are increasingly exposed to various food colorants like carmoisine such studies are highly relevant. In the presence of lysozyme carmoisine absorption spectrum exhibited hypochromic changes. The intrinsic fluorescence of lysozyme was also quenched on interaction. Time-resolved fluorescence results suggested the binding mechanism to involve ground state complexation. The binding was predominatly dominated by non-polyelectrolytic forces. The molecular distance between the donor (lysozyme) and the acceptor (carmoisine), calculated from FRET theory, was found to be 3.37 nms indicating that carmoisine binds close to Trp-62/63 residues in the β-domain of the protein. Information on alterations in the microenvironment surrounding the Trp-residues was also obtained from synchronous fluorescence data. Carmoisine binding induced significant loss in the alpha helical organization of lysozyme. The binding, nevertheless, did not influence the thermal stability of lysozyme significantly. The binding reaction was exothermic and driven by large negative enthalpy and small but favourable entropic contributions. Thioflavin T assay, far-UV circular dichroism studies and AFM imaging testified that carmoisine had a significant inhibitory effect on amyloid fibrillogenesis in lysozyme. Carmoisine also had a definitive defibrillating effect on existing fibrils. The results may provide new insights for designing new small molecule inhibitors for amyloid related diseases.

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Publication details

The article was received on 07 Apr 2017, accepted on 27 May 2017 and first published on 01 Jun 2017


Article type: Paper
DOI: 10.1039/C7MB00207F
Citation: Mol. BioSyst., 2017, Accepted Manuscript
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    Interaction and inhibitory influence of the azo dye carmoisine on lysozyme amyloid fibrillogenesis

    A. Basu and G. Suresh Kumar, Mol. BioSyst., 2017, Accepted Manuscript , DOI: 10.1039/C7MB00207F

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