Figure 25. CryoEM images of lipoprotein particles composed of α-Syn and DOPS (1,2-dioleoyl-sn-glycero-3-phospho-L-serine) and αβ-models of these particles. (a) Side view of the largest type of particle showing its bilayer-type configuration. The yellow dashed rectangle shows the dimensions of our model. (b) Schematic of a side view cross-section of our model showing two α-Syn subunits oriented in opposite directions, drawn to the same scale as the EM images. The orange cylinder = Sy1-3 α-helix, green cylinder = Sy3-4 α-helix, cyan and blue arrows = NAC β-hairpin, gray = lipid alkyl chains, red oval = lipid head group. (c) Flattened side view representation of 4 subunits of the NAC barrel. The black dashed lines are 5 nm apart. The only polar side chain atoms in the central region are hydroxyl groups of T72, T75, S87, and T92; only T72 and T92 are on the interior of the β-barrel and T72 can interact with its counterpart at an axis of 2-fold perpendicular symmetry. Other polar side-chains are near the entrances of the barrel and should have energetically favorable interactions; K80 and K96 should interact with lipid head groups, K97 should salt bridge to E83, N65 should H-bond to Q79. (d) Two antiparallel NAC helical regions (colored as in Fig. 5) and their interactions with lipid headgroups (Orange cylinder = Sy1-3 helix, green cylinder = Sy4-5 helix, red ovals = lipid head groups). (e) Top view of a cryoEM image of the largest particle. Yellow dashed circles were added to illustrate the dimensions of the outer circle (D = 29 nm) that surrounds the dark outer ring, and the next two circles (D = 23 & 11 nm) enclose the light ring. (f) Top view of our model of a Type 2 32mer αβ-barrel. Orange circles = Sy1-3 helices, green cylinders = Sy4-5 helices, blue ring = NAC β-barrel (parameters are below image), red ovals = lipid head groups, gray = lipid alkyl chains. (g-i) Similar representations for models and corresponding cryoEM images for 24mer, 16mer, and 8mer. The cryoEM images were copied with modifications from Eichmann et al. [68].