Tryptophan probes at the alpha-synuclein and membrane interface.
Understanding how environmental factors affect the conformational dynamics of alpha-synuclein (alpha-syn) is of great importance because the accumulation and deposit of aggregated alpha-syn in the brain are intimately connected to Parkinson's disease etiology. Measurements of steady-state and time-resolved fluorescence of single tryptophan-containing alpha-syn variants have revealed distinct phospholipid vesicle and micelle interactions at residues 4, 39, 94, and 125. Our circular dichroism data confirm that Trp mutations do not affect alpha-syn membrane binding properties (apparent association constant K(a)app approximately 1 x 10(7) M(-1) for all synucleins) saturating at an estimated lipid-to-protein molar ratio of 380 or approximately 120 proteins covering approximately 7% of the surface area of an 80 nm diameter vesicle. Fluorophores at positions 4 and 94 are the most sensitive to the lipid bilayer with pronounced spectral blue-shifts (W4: Delta(lambda)max approximately 23 nm; W94: Delta(lambda)max approximately 10 nm) and quantum yield increases (W4, W94: approximately 3 fold), while W39 and W125 remain primarily water-exposed. Time-resolved fluorescence data show that all sites (except W125) have subpopulations that interact with the membrane.
Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Candace M
CM
Pfefferkorn
Jennifer C
JC
Lee
D002942:Circular Dichroism; D008051:Lipid Bilayers / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry*; D051844:alpha-Synuclein / Q000737:chemistry*
D008051:Lipid Bilayers; D051844:alpha-Synuclein; D014364:Tryptophan