Organizing the fluid membrane bilayer: diseases linked to spectrin and ankyrin

Ankyrin and spectrin were first discovered as binding partners in the membrane skeleton of human erythrocytes. Mutations in genes encoding these proteins cause hereditary spherocytosis. Recent advances reveal that ankyrin and spectrin are required for organization of a surprisingly diverse set of proteins, including ion channels and cell adhesion molecules that are localized in specialized membrane domains in many cell types. New insights into the cell biology of ankyrin and spectrin reveal that these proteins actively participate in assembly of specialized membrane domains in addition to their conventional maintenance role as scaffolding proteins. Recently described inherited human diseases due to defects in spectrin or ankyrin include spinocerebellar ataxia type 5 and a cardiac arrhythmia, termed sick sinus syndrome with bradycardia or ankyrin-B syndrome. Together, these studies identify an emerging paradigm for pathogenesis of human disease where failure in cellular localization of membrane-spanning proteins results in loss of physiological function.