Heme Stabilization of α-Synuclein Oligomers during Amyloid Fibril Formation

alpha-Synuclein (aSyn), which forms amyloid fibrils, is linked to the neuronal pathology of Parkinsons disease, as it is the major fibrillar component of Lewy bodies, the inclusions that are characteristic of the disease. Oligomeric structures, common to many neurodegenerative disease-related proteins, may in fact be the primary toxic species, while the amyloid fibrils exist either as a less toxic dead-end species or even as a beneficial mechanism for clearing damaged proteins. To alter the progression of the aggregation and gain insights into the prefibrillar structures, we determined the effect of heme on alpha Syn oligomerization by several different techniques, including native (nondenaturing) polyacrylamide gel electrophoresis, thioflavin T fluorescence, transmission electron microscopy, atomic force microscopy, circular dichroism, and membrane permeation using a calcein release assay. During aggregation, heme is able to bind the alpha Syn in a specific fashion, stabilizing distinct oligomeric conformations and promoting the formation of alpha Syn into annular structures, thereby delaying and/or inhibiting the fibrillation process. These results indicate that heme may play a regulatory role in the progression of Parkinsons disease; in addition, they provide insights into how the aggregation process may be altered, which may be applicable to the understanding of many neurodegenerative diseases.