Clioquinol-induced ordered conformational behavior in alpha-synuclein: promising relevance for therapeutic approach to Parkinson's disease



Parkinson?¦s disease (PD) is a devastating and an intricate complex neurological disorder that results from the progressive degeneration of nerve cells in Substantia nigra that controls movement. The pathological hallmark of PD is the formation of insoluble protein aggregates known as lewey bodies. Alpha-synuclein is the major constituent of these fibrillar structures. Alpha-synuclein a 140 amino acid pre-synaptic protein is natively unfolded, random coiled conformation, but n Lewey bodies and neuritic plaques it has cross beta conformation. There is a great need to look for biomolecules that favors and stabilizes ordered conformation in alpha-synuclein and thus of great therapeutic application. The formation of alpha-helix is a protective mechanism against beta sheet and prevents aggregation. In this perspective, we investigated the role of a metal chelator, clioquinol, in inducing ordered structure in alpha-synuclein. Interestingly, circular dichroism spectroscopic studies on alpha-synuclein-clioquinol interaction revealed that there is a characteristic minimum at 198 nm and at a short amplitude of 222 nm, which confers the formation of alpha-helix. The formation of alpha-helix in alpha-synuclein by clioquinol is verified by fluorescence spectroscopic studies like 8-Anilino NitrosulphonicAcid binding, Intrinsic Tyrosine Fluorescence and Acrylamide quenching studies. The stability of alpha-helix of synuclein was characterized by CD-Tm studies and found an increase in Tm values (Syn alone- 41 degree, Syn+CQ-49.8 degree) compared to Synuclein alone Hence, the alpha-helix formed by clioquinol is thermodynamically stable. This is further supported by studies carried out at lower pHs, melting temperature studies and chemical denaturation studies using Urea and GdHcl. To the best of our knowledge, this is the first study to show the relevance of clioquinol in developing of therapeutic strategies in Parkinson’s disease by understanding the conformational pattern of alpha-synuclein.