Practice question

Erythrocyte mechanical stability depends on vertical linkages mediated by ankyrin-R isoform one hundred ninety kilodaltons to two hundred ten kilodaltons comprising three distinct domains enabling integration. N-terminal membrane binding domain contains twenty four tandem ankyrin repeats each thirty three residues forming elongated superhelical solenoid that creates concave binding surface recognizing cytoplasmic loop of Band 3 anion exchanger between residues one hundred seventy five to one hundred eighty five with nanomolar affinity, also binding Na K ATPase alpha subunit, voltage gated sodium channel Nav1.5, and L1 cell adhesion molecule in neurons and muscle. Central spectrin binding domain binds beta spectrin repeat fourteen to fifteen near ankyrin repeat. C-terminal regulatory domain contains death domain and C-terminal extension modulating affinity through autoinhibition. Bridging spectrin-actin lattice to integral proteins prevents membrane vesiculation and maintains deformability required for circulatory passage through three micrometer splenic interendothelial slits. Hereditary mutations account for about fifty percent hereditary spherocytosis with reduced spectrin assembly spherical rigid cells hemolysis and jaundice, illustrating cytoskeletal anchorage role.