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

Removing or preventing the formation of alpha-synuclein aggregates is a plausible strategy against Parkinson's disease. To this end, we have engineered the beta-wrapin AS69 to bind monomeric alpha-synuclein with high affinity. In cultured cells, AS69 reduced the self-interaction of a synuclein and formation of visible alpha-synuclein aggregates. In flies, AS69 reduced alpha-synuclein aggregates and the locomotor deficit resulting from alpha-synuclein expression in neuronal cells. In biophysical experiments in vitro, AS69 highly sub-stoichiometrically inhibited both primary and autocatalytic secondary nucleation processes, even in the presence of a large excess of monomer. We present evidence that the AS69-alpha-synuclein complex, rather than the free AS69, is the inhibitory species responsible for sub-stoichiometric inhibition of secondary nucleation. These results represent a new paradigm that high affinity monomer binders can lead to strongly sub-stoichiometric inhibition of nucleation processes.