Spectrin, Cytoskeletons and Hereditary Spherocytosis

[liveonearth]

spectrin = cytoskeletal protein
lines inner plasma membrane
pentagonal or hexagonal arrangements
scaffolding
maintains membrane integrity/structure
production of spectrin is promoted by the transcription factor GATA1.
in myocardial cells: αII spectrin distribution is coincident with Z-discs & plasma membrane of myofibrils
mice with an ankyrin (ankB) knock-out have disrupted calcium homeostasis in the myocardia, disrupted z-band and sarcomere morphology
Spectrin repeats found in several proteins involved in cytoskeletal structure
incl: spectrin, alpha-actinin and dystrophin
spectrin repeat forms a three-helix bundle
hexagons = tetramers of spectrin associating with short actin filaments connecting it all at either end
in some brain injury (diffuse axonal inj) spectin is cleaved by calpain (proteolytic enzyme)-->membrane forms blebs-->blows up-->cell dies

IN RBC's
dimeric spectrin is formed by the lateral association of αI and βI monomers
dimers associate head-to-head-->tetramer
tetramers assoc head-to-head with short actin filaments-->hexagonal complexes
spectrin forms the meshwork that provides red blood cells their shape
mutations in spectrin-->hereditary elliptocytosis and hereditary spherocytosis