Structural and Dynamical Insights into the Membrane-Bound α-Synuclein

Abstract

Membrane-induced disorder-to-helix transition of α-synuclein, a presynaptic protein, has been implicated in a number of important neuronal functions as well as in the etiology of Parkinson’s disease. In order to obtain structural insights of membrane-bound α-synuclein at the residue-specific resolution, we took advantage of the fact that the protein is devoid of tryptophan and incorporated single tryptophan at various residue positions along the sequence. These tryptophans were used as site-specific markers to characterize the structural and dynamical aspects of α-synuclein on the negatively charged small unilamellar lipid vesicles. An array of site-specific fluorescence readouts, such as the spectral-shift, quenching efficiency and anisotropy, allowed us to discern various features of the conformational rearrangements occurring at different locations of α-synuclein on the lipid membrane. In order to define the spatial localization of various regions of the protein near the membrane surface, we utilized a unique and sensitive indicator, namely, red-edge excitation shift (REES), which originates when a fluorophore is located in a highly ordered micro-environment. The extent of REES observed at different residue positions allowed us to directly identify the residues that are localized at the membrane-water interface comprising a thin (∼ 15 Å) layer of motionally restrained water molecules and enabled us to construct a dynamic hydration map of the protein. The combination of site-specific fluorescence readouts allowed us to unravel the intriguing molecular details of α-synuclein on the lipid membrane in a direct model-free fashion. Additionally, the combination of methodologies described here are capable of distinguishing subtle but important structural alterations of α-synuclein bound to different negatively charged lipids with varied head-group chemistry. We believe that the structural modulations of α-synuclein on the membrane could potentially be related to its physiological functions as well as to the onset of Parkinson’s diseases.

Molecular Details of α-Synuclein Membrane Association Revealed by Neutrons and Photons

“…39,70–71 WT α-syn is devoid of Trp residues, enabling single-Trp incorporation as local fluorescent probes. It is well-established that Trp membrane penetration can be monitored via fluorescence quenching by the heavy-atom bromine incorporated at specific positions along the lipid hydrocarbon chain.…”

The red edge excitation shift phenomenon can be used to unmask protein structural ensembles: implications for NEMO–ubiquitin interactions

“…The REES effect is, therefore, a unique probe for proteins with a high degree of molecular flexibility resulting in an ensemble of solvent environments around the Trp probe. For proteins, such an ensemble may arise from a broad equilibrium of conformational states, such as in molten globule intermediates of highly flexible or dynamic proteins [14,16,17].…”

Therapeutic Potential of Baicalein in Parkinson’s Disease: Focus on Inhibition of α-Synuclein Oligomerization and Aggregation

“…Importantly, multifunctional properties of α-syn are predicted by its structure that has been attributed to this protein [33]. The structure flexibility property of α-syn allows it to accept a wide range of conformations depending on binding partners and environment [34,35]. Because of its abundant presence at presynaptic terminals, chaperone function of α-syn is the key cellular function, which controls the exocytosis through trafficking and organizing the synaptic vesicle pool.…”

“…Many studies have clearly demonstrated that baicalein protected 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenylpyridinium (MPP+), glutamate, amyloid-β (Aβ), hydrogen peroxide (H 2 O 2 ), 1-methyl-4-phenyl-1,2,3,6tetrahydropyridine (MPTP), and methamphetamine-induced neurotoxicity in animal models and cell lines [27][28][29][30][31][32][33]. Earlier, some authors clearly reviewed the anticancer, anti-inflammatory, cardioprotective properties, ocular disorders, and mitochondrial function [34][35][36][37]. Li et al [38] briefed the therapeutic properties of baicalein against PD.…”