Differential regulation of wild-type and mutant alpha-synuclein binding to synaptic membranes by cytosolic factors

BACKGROUND: Alpha-Synuclein (α-syn), a 140 amino acid protein associated with presynaptic membranes in brain, is a major constituent of Lewy bodies in Parkinson's disease (PD). Three missense mutations (A30P, A53T and E46K) in the α-syn gene are associated with rare autosomal dominant forms of familial PD. However, the regulation of α-syn's cellular localization in neurons and the effects of the PD-linked mutations are poorly understood. RESULTS: In the present study, we analysed the ability of cytosolic factors to regulate α-syn binding to synaptic membranes. We show that co-incubation with brain cytosol significantly increases the membrane binding of normal and PD-linked mutant α-syn. To characterize cytosolic factor(s) that modulate α-syn binding properties, we investigated the ability of proteins, lipids, ATP and calcium to modulate α-syn membrane interactions. We report that lipids and ATP are two of the principal cytosolic components that modulate Wt and A53T α-syn binding to the synaptic membrane. We further show that 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16:0 PAF) is one of the principal lipids found in complex with cytosolic proteins and is required to enhance α-syn interaction with synaptic membrane. In addition, the impaired membrane binding observed for A30P α-syn was significantly mitigated by the presence of protease-sensitive factors in brain cytosol. CONCLUSION: These findings suggest that endogenous brain cytosolic factors regulate Wt and mutant α-syn membrane binding, and could represent potential targets to influence α-syn solubility in brain.