Which cytoskeletal protein lets erythrocytes fold and then spring back in narrow vessels?

1. Capillary beds can be narrower than the erythrocyte itself, so the cell must fold to pass. 2. Spectrin is the flexible cytoskeletal element that allows that folding and the recoil afterwards. 3. Loss of this deformability is exactly what makes sickled cells lodge in capillaries. 4. Transferrin and hemosiderin handle iron transport and storage, and fibrinogen is a clotting precursor, so none of the three is structural to the red cell. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 18 "The Cardiovascular System: Blood", section 18.3 Erythrocytes_