The aggregation of human alpha-synuclein
(hαS) is pivotally
implicated in the development of most types of synucleinopathies.
Molecules that can inhibit or reverse the aggregation process of amyloidogenic
proteins have potential therapeutic value. The anti-aggregating activity
of multiple carotenoid compounds has been reported over the past decades
against a growing list of amyloidogenic polypeptides. Here, we aimed
to determine whether crocin, the main carotenoid glycoside component
of saffron, would inhibit hαS aggregation or could disassemble
its preformed fibrils. By employing a series of biochemical and biophysical
techniques, crocin was exhibited to inhibit hαS fibrillation
in a dose-dependent fashion by stabilizing very early aggregation
intermediates in off-pathway non-toxic conformations with little β-sheet
content. We also observed that crocin at high concentrations could
efficiently destabilize mature fibrils and disassemble them into seeding-incompetent
intermediates by altering their β-sheet conformation and reshaping
their structure. Our atomistic molecular dynamics (MD) simulations
demonstrated that crocin molecules bind to both the non amyloid-β
component (NAC) region and
C-terminal domain of hαS. These interactions could thereby stabilize
the autoinhibitory conformation of the protein and prevent it from
adopting aggregation-prone structures. MD simulations further suggested
that ligand molecules prefer to reside longitudinally along the fibril
axis onto the edges of the inter-protofilament interface where they
establish hydrogen and hydrophobic bonds with steric zipper stabilizing
residues. These interactions turned out to destabilize hαS fibrils
by altering the interstrand twist angles, increasing the rigidity
of the fibril core, and elevating its radius of gyration. Our findings
suggest the potential pharmaceutical implication of crocin in synucleinopathies.