An engineered monomer binding-protein for α-synuclein efficiently inhibits the proliferation of amyloid fibrils

Removing or preventing the formation of α- synucleinaggregates is a plausible strategy against Parkinson9s disease. To this end we have engineered the β-wrapin AS69 to bind monomeric α- synucleinwith high affinity. In cultured cells, AS69 reduced the occurrence of α- synucleinoligomers and of visible α- synucleinaggregates. In flies, AS69 reduced α- synucleinaggregates and the locomotor deficit resulting from α- synucleinexpression in neuronal cells. In a mouse model based on the intracerebral injection of pre-formed α- synucleinseed fibrills (PFFs), AS69 co-injection reduced the density of dystrophic neurites observed three months later. In biophysical experiments in vitro, AS69 highly sub-stoichiometrically inhibited auto-catalytic secondary nucleation processes, even in the presence of a large excess of monomer. We present evidence that the AS69-α- synucleincomplex, rather than the free AS69, is the inhibitory species responsible for sub-stoichiometric inhibition. These results represent a new paradigm that high affinity monomer binders can be strongly sub-stoichiometric inhibitors of nucleation processes.