Figure 5.

Three-dimensional topology of the membrane skeleton. (A and B) Histogram of the number of spectrin connections per junctional complex for frozen-hydrated and negatively stained skeletons, respectively. For frozen-hydrated skeletons, the mean ± SD of spectrin connections/junctional complex was 4.2 ± 1.0 (range 1–6, n = 133). For negatively stained skeletons, the mean ± SD was 5.2 ± 0.7 nm (range 4–7 nm, n = 35). (C) Skeletonized, volume-rendering of two junctional complexes (yellow) with their associated spectrin filaments (red and blue). A spectrin heterotetramer connecting the two junctional complexes is highlighted in magenta. The two views are related by a 180° rotation. Scale bar, 50 nm. (D) Tomographic slices at intervals of 9 nm through these same junctional complexes (black arrows), showing the spectrin filaments (white arrowheads). Scale bar, 35 nm. Also see Movie S3 and another example of local network topology in Fig. S4.