Beta Amyloid Peptide: Research Paper : α-Synuclein facilitates endocytosis by elevating the steady-state levels of phosphatidylinositol 4,5-bisphosphate

α-Synuclein facilitates endocytosis by elevating the steady-state levels of phosphatidylinositol 4,5-bisphosphate

Abstract

α-Synuclein (α-Syn) is a protein implicated in the pathogenesis of Parkinson's disease (PD). It is an intrinsically disordered protein that binds acidic phospholipids. Growing evidence supports a role for α-Syn in membrane trafficking, including, mechanisms of endocytosis and exocytosis, although the exact role of α-Syn in these mechanisms is currently unclear. Here we investigate the associations of α-Syn with the acidic phosphoinositides (PIPs), phosphatidylinositol 4,5-bisphosphate (PI4,5P2) and phosphatidylinositol 3,4-bisphosphate (PI3,4P2). Our results show that α-Syn colocalizes with PIP2 and the phosphorylated active form of the clathrin adaptor protein 2 (AP2) at clathrin-coated pits. Using endocytosis of transferrin as an indicator for clathrin mediated endocytosis (CME), we find that α-Syn involvement in endocytosis is specifically mediated through PI4,5P2 levels on the plasma membrane. In accord with their effects on PI4,5P2 levels, the PD associated A30P, E46K and A53T mutations in α-Syn further enhance CME in neuronal and non-neuronal cells. However, Lysine to Glutamic acid substitutions at the KTKEGV repeat domain of α-Syn, that interfere with phospholipid binding, are ineffective in enhancing CME. We further show that the rate of synaptic vesicle (SV) endocytosis is differentially affected by the α-Syn mutations and associates with their effects on PI4,5P2 levels, however, with the exception of the A30P mutation. This study provides evidence for a critical involvement of PIPs in α-Syn-mediated membrane trafficking.

Keywords: alpha-synuclein (a-synuclein); clathrin; endocytosis; phosphoinositide; synapse.

Published under license by The American Society for Biochemistry and Molecular Biology, Inc.

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