Depth of α-synuclein in a bilayer determined by fluorescence, neutron reflectometry, and computation.
α-Synuclein (α-syn) membrane interactions are implicated in the pathogenesis of Parkinson's disease. Fluorescence and neutron reflectometry (NR) measurements reveal that α-syn penetrates ∼9-14 Å into the outer leaflet of the bilayer, with a substantial portion of the membrane-bound polypeptide extending into the aqueous solvent. For the first time, to our knowledge, we used NR to obtain direct quantitative evidence of α-syn-induced membrane thinning. To examine the effect of specific residues on membrane penetration depths, we used a series of W4-containing N-terminal peptides. We identified that the first 15 residues (P15) nearly recapitulate the features of the full-length protein (i.e., partition constants, molecular mobility, and insertion of the W4 side chain into the bilayer), and found that as few as the first four N-terminal residues are sufficient for vesicle binding. Although at least one imperfect amphipathic repeat sequence (KAKEGV) is required for α-helical formation, secondary structural formation has little effect on membrane affinity. To develop an N-terminal α-syn model for bilayer interactions, we performed molecular-dynamics simulations of the P15 peptide submerged in a bilayer. The simulation results are highly consistent with experimental data indicating a broad low-energy region (8.5-14.5 Å) for W4 insertion.
Laboratory of Molecular Biophysics, National Institutes of Health, Bethesda, Maryland, USA.
Candace M
CM
Pfefferkorn
Frank
F
Heinrich
Alexander J
AJ
Sodt
Alexander S
AS
Maltsev
Richard W
RW
Pastor
Jennifer C
JC
Lee
D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D033363:Neutron Diffraction; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D051844:alpha-Synuclein / Q000737:chemistry* / Q000378:metabolism
D008051:Lipid Bilayers; D010446:Peptide Fragments; D010743:Phospholipids; D051844:alpha-Synuclein