Site-Specific Hydration Dynamics Illuminates the Key Structural Features of Membrane-Bound α-Synuclein

Abstract

α-Synuclein is an intrinsically disordered protein that is preferentially expressed in presynaptic nerve terminals. It undergoes a large-scale conformational rearrangement upon binding to synaptic vesicle membranes. In order to obtain the structural insights into the membrane-bound α-synuclein at the residue-specific resolution, we incorporated single tryptophan at various locations along the sequence. These tryptophans were used as site-specific fluorescence markers to characterize the structural and dynamical aspects of α-synuclein. The spatial localization of various parts of the protein near the membrane surface was elucidated utilizing a unique and sensitive fluorescence readout, 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 locations allowed us to directly identify the residues that are localized at the membrane-water interface comprising a thin (∼15 A) layer of motionally-constrained water molecules (Figure 1). Additionally, we have been able to distinguish subtle but important structural differences of α-synuclein bound to different lipids membranes. 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.View Large Image | View Hi-Res Image | Download PowerPoint Slide