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Explorations of the application of cyanine dyes for quantitative α-synuclein detection

We examined the practical aspects of using fluorescent mono (T-284) and trimethinecyanine (SH-516) dyes for detecting and quantifying fibrillar α-synuclein (ASN). We studied the interaction of cyanine dyes with fibrillar proteins using fluorescence spectroscopy and atomic force microscopy. The commercially available classic amyloid stain thioflavin T (Thio T) was used as the reference dye. T-284 and SH-516 dyes can be used for fluorometric quantification of fibrillar wild-type ASN at concentrations of ∼1.5–20 µg/ml. Both dyes appeared suitable for step-wise monitoring of ASN variants (wild-type and mutants A30P and A53T) aggregation into fibrils in vitro, demonstrating good reproducibility, exceeding that for the commonly used Thio T. Our assay may be used for screening in vitro of agents capable of affecting the aggregation of ASN. In addition, T-284 and SH-516 cyanine dyes were shown to recognize amyloid proteins of various amino acid compositions selectively. T-284 demonstrated particular sensitivity to wild-type and A53T ASN, while for SH 516, the fluorescence response to fibrillar proteins was nearly the same except for lysozymes. T-284 and SH-516 cyanine dyes are sensitive and specific fluorescent probes for monitoring ASN fibril formation process in vitro, quantification of fibrillar ASN in solution, and fluorescent detection of various fibrillar protein species.