De-aggregation mediated monitoring of protein aggregation through controlled aggregation of cyanine dyes

Cyanine dyes have been widely used as fluorescent reporters (Mishra, A., et al 2000) for tracking and studying the interaction of various biomolecules, mainly based on the impressive quantum yields of the dyes. Cyanine dyes also possess distinctive self-aggregation properties and have been shown to self-assemble into a variety of structures such as dimers, H-aggregates and J-aggregates (Kasha et al., 1965). In contrast to the impressive emission characteristics of J-aggregates, the fluorescence of H-dimers and H-aggregates is quenched. Bio molecular interactions that are able to selectively de-aggregate the H-dimers and aggregates can be tracked by the consequent fluorescence turn-on (Xu, Y. et al 2010). We have recently developed a series of benzothiazole-based dimeric cyanine dyes that possess the propensity to form specific aggregates in a controlled manner. In this work we explore the de-aggregation of novel cyanine dyes by proteins and investigate the fluorescence turn-on as a mechanism for sensing the proteins and their interactions. Sub-nanomolar levels of several proteins can be detected by our approach. Further, we investigate the aggregation of BSA and HSA through de-aggregation of dimeric cyanine dyes. The observed aggregation patterns are analogous to that reported by non-covalent labels such as Thioflavin T. Finally, we also investigate the prospects of using our dimeric cyanine dyes as agents that can modulate or hinder the aggregation of proteins such as tau-beta and alpha-synuclein. The ability of the dimeric dyes to report such interactions is in sharp contrast to their conventional monomeric counterparts. Our results show that the novel dimeric cyanine dyes hold promise both as non-covalent reporters of protein concentration and their interactions as well as molecules that could be used especially in the context of neuro-degenerative disorders.