Figure 1.

Schematic picture of the spontaneous curvature of the two types of spectrin filaments on the RBC membrane: (A) type I spectrin filaments that are grafted at one end (left), or at both ends but not connected to the stretched network, induce a concave spontaneous curvature of radius R₁ (R_g is the radius of gyration of the filament). (B) Type II spectrin filaments that are grafted at both ends and are part of the connected stretched network that spans the RBC membrane's inner surface (L is the separation between anchoring complexes) induce a local convex spontaneous curvature of radius R₂. An illustration of type I (C) and type II (D) filaments as part of a triangular network in which each edge represents a spectrin tetramer that can be connected to the membrane through actin band 4 complexes (black circles) and can be further connected to the membrane through band 3 complexes (open circles) is shown. In c the spectrin tetramers are anchored to membrane complexes only at one end (type I), whereas in D the spectrin tetramers are anchored at both ends and are part of the stretched network (type II). (E) Schematic illustration of the curling RBC ghost, which has a cylindrical symmetry, and the thin-strip approximation (F) that we use in our calculation. The strip has width w and a contour defined by the coordinate s, and the forces act everywhere along the local normal $\overrightarrow{n}$.