Interaction of the Molecular Chaperone αB-Crystallin with α-Synuclein: Effects on Amyloid Fibril Formation and Chaperone Activity

Abstract

α-Synuclein is a pre-synaptic protein, the function of which is not completely understood, but its pathological form is involved in neurodegenerative diseases. In vitro, α-synuclein spontaneously forms amyloid fibrils. Here, we report that αB-crystallin, a molecular chaperone found in Lewy bodies that are characteristic of Parkinson's disease (PD), is a potent in vitro inhibitor of α-synuclein fibrillization, both of wild-type and the two mutant forms (A30P and A53T) that cause familial, early onset PD. In doing so, large irregular aggregates of α-synuclein and αB-crystallin are formed implying that αB-crystallin redirects α-synuclein from a fibril-formation pathway towards an amorphous aggregation pathway, thus reducing the amount of physiologically stable amyloid deposits in favor of easily degradable amorphous aggregates. α-Synuclein acts as a molecular chaperone to prevent the stress-induced, amorphous aggregation of target proteins. Compared to wild-type α-synuclein, both mutant forms have decreased chaperone activity in vitro against the aggregation of reduced insulin at 37 °C and the thermally induced aggregation of βL-crystallin at 60 °C. Wild-type α-synuclein abrogates the chaperone activity of αB-crystallin to prevent the precipitation of reduced insulin. Interaction between these two chaperones and formation of a complex are also indicated by NMR spectroscopy, size-exclusion chromatography and mass spectrometry. In summary, α-synuclein and αB-crystallin interact readily with each other and affect each other's properties, in particular α-synuclein fibril formation and αB-crystallin chaperone action.