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. 2013 Jul 22;8(7):e69410. doi: 10.1371/journal.pone.0069410

Figure 6. Pairing of connection sites of nubs with connection sites of AZM and non-AZM macromolecules.

Figure 6

(A,B) Surface model of the membrane of a docked vesicle in one of the primary reconstructions; (A) shows the hemisphere facing the main body of the AZM and (B) shows the hemisphere facing away from the main body. (A-left, B-left) Three-voxel-thick terminal portions of the AZM’s ribs (gold), spars (red), booms (purple) and pins (copper) and of non-AZM macromolecules (pewter), mark the connection site of each on the outer cytosolic surface of the vesicle membrane (pale blue). The vesicle’s fusion domain is indicated by the dashed line (B). (A-right, B-right) The AZM and non-AZM macromolecules are disabled on the surface model and the membrane has been made almost transparent. Three-voxel-thick terminal portions of the luminal assembly’s nubs (blue) mark the connection site of each on the luminal surface of the vesicle membrane. The distribution of the connection sites of the nubs is non-uniform and appears similar to the asymmetric distribution of the connection sites of the AZM and non-AZM macromolecules, although some of the similarity is obscured in these 2D images by the vesicle’s 3D curvature and the difference in the vesicle’s luminal and outer diameters. (C) Using x,y,z coordinates of the connection sites in (A,B), after correcting for the difference between luminal and outer diameters of the vesicle membrane, the relative positions of the centroids of the connection sites of the AZM and non-AZM macromolecules and of the nubs were plotted on a 2D Robinson map. The centroids were overlaid by filled circles slightly smaller in diameter than the connection sites and color-coded as in (A,B). The hemisphere of the vesicle facing the main body of the AZM lies between the bold longitudinal lines. The main AZM binding domain, which covers about 20% of the outer surface area of this vesicle and includes about half of the total nub and AZM/non-AZM macromolecule connection sites on the membrane, is encircled by the solid white line. Each nub is paired with an AZM or non-AZM macromolecule lying opposite to, or slightly offset from, it.