Role of α‐synuclein penetration into the membrane in the mechanisms of oligomer pore formation

Abstract

Parkinson’s disease (PD) and Dementia with Lewy bodies are common disorders of the aging population characterized by the progressive accumulation of α-synuclein (α-syn) in the CNS. Aggregation of α-syn into oligomers with a ring-like appearance has been proposed a role in toxicity. However, the molecular mechanisms and the potential sequence of events involved in the formation of pore-like structures are unclear. We utilized computer modeling and cell-based studies to investigate the process of α-syn (wild type and A53T) oligomerization in membranes. The studies suggest that α-syn rapidly penetrates the membrane, changing its conformation from α-helical toward a coiled structure. This penetration facilitate the incorporation of additional α-syn monomers to the complex, and subsequent displacement of phospholipids, and formation of oligomers in the membrane. This process occurred more rapidly, and with more favorable energy of interaction for mutant A53T compared with wild type α-syn. After 4 ns of simulation for the protein-membrane model α-syn penetrated through two thirds of the membrane. By 9 ns, the penetration of the annular α-syn oligomers can result in the formation of pore-like structures that fully perforate the lipid bilayer. Experimental incubation of recombinant α-syn in synthetic membranes resulted in the formation of similar pore-like complexes. Moreover, mutant (A53T) α-syn had a greater tendency to accumulate in neuronal membrane fractions in cell cultures, resulting in greater neuronal permeability with the calcein efflux assay. These studies provide a sequential molecular explanation for the process of α-syn oligomerization in the membrane, and support the role of formation of pore-like structures in the pathogenesis of the neurodegenerative process in PD.

Lys-63-linked Ubiquitination by E3 Ubiquitin Ligase Nedd4-1 Facilitates Endosomal Sequestration of Internalized α-Synuclein

“…Several possibilities have been postulated, including direct penetration (25), the formation of annular pore-like structures (28), and macropinocytosis (5,29). Although this notion is provocative, it is supported by analogous studies in other neurodegenerative diseases, such as polyglutamine disease, in which polyQ aggregates can rapidly enter the cytosolic compartment of mammalian cells and nucleate the aggregation of soluble proteins with these polyQ tracts (30).…”

Potential Pathways of Abnormal Tau and α-Synuclein Dissemination in Sporadic Alzheimer's and Parkinson's Diseases

“…In addition, within the context of proteinopathies, in which the degradation and removal of abnormal proteins malfunction, both are linked with considerable certainty to the pathogenic process, because the breakdown of cellular mechanisms for degrading and clearing abnormal tau and a-synuclein make them ultimately deleterious to neuronal equilibrium (Chung et al 2001;Ciechanover 2005;Olanow and McNaught 2006;Rubinsztein 2006;Lim and Tan 2007;Upadhya and Hegde 2007a,b;Pan et al 2008;Lehman 2009;Kovacech et al 2010;Ebrahimi-Fakhari et al 2012;Kopeikina et al 2012;Tai et al 2012). There is also evidence that intra-axonal a-synuclein and intraneuronal tau aggregates are associated with axonopathy (Irizarry et al 1998;Saha et al 2004;Duda et al 2006;Stokin and Goldstein 2006;Orimo et al 2008;Kanazawa et al 2011;Lingor et al 2012;Lamberts et al 2015), cell membrane dysfunction (Tsigelny et al 2012), or cellular dysfunction (Dugger and Dickson 2010). Depending on study design, some experimental models display motor impairment, cognitive impairment, or deficits in neuronal excitability and/or cell loss (Giasson et al 2002;Sydow et al 2011;Volpicelli-Daley et al 2011;Luk et al 2012a;Sacino et al 2014;Brelstaff et al 2015;Ozcelik et al 2016).…”

Targeting α-Synuclein as a Parkinson’s Disease Therapeutic

“…This definition as applied to the ensemble of α-synuclein oligomers would include not only their general size (i.e., small, medium, large) [94] but also their secondary structure characteristics including β-sheet content and arrangement [95,96] and α-helical content [40], overall 3-dimensional shape (morphology) [30,[97][98][99][100], reactivity with conformation and epitope-specific antibodies [101,102], and whether they are "on" [103] or "off" [32,[104][105][106] pathway to fibril formation. In addition, there are "operational definitions" that classify α-synuclein oligomers in terms of their biochemical characteristics or function, including protease resistance [32], effect on cell viability [96,107,108], ability to generate reactive oxygen species [32], recruit or activate microglia [109,110], bind to lipids [40], and form pores in lipid bilayers [103,[111][112][113][114][115]. In some cases, oligomers are formed as a result of an interaction with an exogenous small molecule [116,117], and some of these oligomers are "off-pathway" to fibril formation, but yet they may share some characteristics with "on-pathway" oligomers (see Sect.…”