A Combinatorial Code for the Interaction of α-Synuclein with Membranes

Abstract

Considerable genetic and pathological evidence has implicated the small, soluble protein ␣-synuclein in the pathogenesis of familial and sporadic forms of Parkinsons disease (PD). However, the precise role of ␣-synuclein in the disease process as well as its normal function remain poorly understood. We recently found that an interaction with lipid rafts is crucial for the normal, pre-synaptic localization of ␣-synuclein. To understand how ␣-synuclein interacts with lipid rafts, we have now developed an in vitro binding assay to rafts purified from native membranes. Recapitulating the specificity observed in vivo, recombinant wild type but not PD-associated A30P mutant ␣-synuclein binds to lipid rafts isolated from cultured cells and purified synaptic vesicles. Proteolytic digestion of the rafts does not disrupt the binding of ␣-synuclein, indicating an interaction with lipid rather than protein components of these membranes. We have also found that ␣-synuclein binds directly to artificial membranes whose lipid composition mimics that of lipid rafts. The binding of ␣-synuclein to these raft-like liposomes requires acidic phospholipids, with a preference for phosphatidylserine (PS). Interestingly, a variety of synthetic PS with defined acyl chains do not support binding when used individually. Rather, the interaction with ␣-synuclein requires a combination of PS with oleic (18:1) and polyunsaturated (either 20:4 or 22:6) fatty acyl chains, suggesting a role for phase separation within the membrane. Furthermore, ␣-synuclein binds with higher affinity to artificial membranes with the PS head group on the polyunsaturated fatty acyl chain rather than on the oleoyl side chain, indicating a stringent combinatorial code for the interaction of ␣-synuclein with membranes.

Specificity and Kinetics of α-Synuclein Binding to Model Membranes Determined with Fluorescent Excited State Intramolecular Proton Transfer (ESIPT) Probe

“…Early studies showed that the binding of AS to extracts of brain tissue lipid membranes did not require the presence of other proteins (27), and therefore AS also binds readily to artificial membranes (4,(27)(28)(29)(30). Because the lipophilic N-terminal part of AS is positively charged, the protein has a preference for anionic membranes (28).…”

Glucocerebrosidase, a new player changing the old rules in Lewy body diseases

“…These changes in glycosphingolipids may particularly affect lipid raft function by interfering with the sorting and trafficking of proteins and lipids associated with the rafts. Notably, α -synuclein is localized in some of the lipid rafts in neuronal cells (Fortin et al , 2004 ;Kubo et al , 2005 ). Therefore, it is speculated that GBA1 mutation-induced lipid changes may alter the interaction between lipid microdomains and α -synuclein.…”

“…Alterations in membrane lipid composition are thought to be an important factor affecting the interaction between α -synuclein and lipid membranes (Kubo et al , 2005 ). Changes in lipid composition may occur through oxidative modifications or metabolic alterations ( O ' Donnell et al, 1999 ;Mosca et al , 2011 ).…”

Progress in the pathogenesis and genetics of Parkinson's disease

“…Biskup et al (2006) also reported the presence of LRRK2 in membrane structures, such as lysosomes, endosomes, transport vesicles and mitochondria. In this regard it is interesting to note that a-synuclein is also expressed in the presynaptic membranes and lipid rafts (Fortin et al 2004;Kubo et al 2005).…”

“…The mutant a-synuclein has increased tendency for self-aggregation (El Agnaf et al 1998). a-Synuclein is mainly located in the lipid raft in membranes (Fortin et al 2004;Kubo et al 2005) and this localization appears to be important in the trafficking of a-synuclein and its final localization in presynaptic and synaptic vesicular membranes.…”